diff options
Diffstat (limited to 'erts/doc/src')
38 files changed, 630 insertions, 140 deletions
diff --git a/erts/doc/src/Makefile b/erts/doc/src/Makefile index 89d7c85a86..d4c6fe67d2 100644 --- a/erts/doc/src/Makefile +++ b/erts/doc/src/Makefile @@ -78,6 +78,7 @@ XML_CHAPTER_FILES = \ erl_ext_dist.xml \ erl_dist_protocol.xml \ communication.xml \ + time_correction.xml \ notes.xml \ notes_history.xml diff --git a/erts/doc/src/absform.xml b/erts/doc/src/absform.xml index e512c19e05..55aef9f8ab 100644 --- a/erts/doc/src/absform.xml +++ b/erts/doc/src/absform.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> diff --git a/erts/doc/src/alt_dist.xml b/erts/doc/src/alt_dist.xml index 038950b54d..e4912576f7 100644 --- a/erts/doc/src/alt_dist.xml +++ b/erts/doc/src/alt_dist.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> - <year>2000</year><year>2011</year> + <year>2000</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/book.xml b/erts/doc/src/book.xml index 00a2888685..dc02edc5c6 100644 --- a/erts/doc/src/book.xml +++ b/erts/doc/src/book.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE book SYSTEM "book.dtd"> <book xmlns:xi="http://www.w3.org/2001/XInclude"> <header titlestyle="normal"> <copyright> - <year>1997</year><year>2009</year> + <year>1997</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/communication.xml b/erts/doc/src/communication.xml index 61a9b0e716..02040c9edb 100644 --- a/erts/doc/src/communication.xml +++ b/erts/doc/src/communication.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> diff --git a/erts/doc/src/crash_dump.xml b/erts/doc/src/crash_dump.xml index 8f5515baca..c59741f250 100644 --- a/erts/doc/src/crash_dump.xml +++ b/erts/doc/src/crash_dump.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> diff --git a/erts/doc/src/driver.xml b/erts/doc/src/driver.xml index 52283879c7..616703fdef 100644 --- a/erts/doc/src/driver.xml +++ b/erts/doc/src/driver.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> - <year>2001</year><year>2011</year> + <year>2001</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/driver_entry.xml b/erts/doc/src/driver_entry.xml index c37138e7b1..48dfcb09b1 100644 --- a/erts/doc/src/driver_entry.xml +++ b/erts/doc/src/driver_entry.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE cref SYSTEM "cref.dtd"> <cref> <header> <copyright> - <year>2001</year><year>2012</year> + <year>2001</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -110,6 +110,8 @@ <p>When the driver has passed the <c>driver_entry</c> over to the emulator, the driver is <em>not</em> allowed to modify the <c>driver_entry</c>.</p> + <p>If compiling a driver for static inclusion via --enable-static-drivers you + have to define STATIC_ERLANG_DRIVER before the DRIVER_INIT declaration.</p> <note> <p>Do <em>not</em> declare the <c>driver_entry</c> <c>const</c>. This since the emulator needs to modify the <c>handle</c>, and the <c>handle2</c> diff --git a/erts/doc/src/epmd.xml b/erts/doc/src/epmd.xml index 3e7005410f..963d35c3c8 100644 --- a/erts/doc/src/epmd.xml +++ b/erts/doc/src/epmd.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1996</year><year>2011</year> + <year>1996</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/erl.xml b/erts/doc/src/erl.xml index c16b45856d..bf0d132955 100644 --- a/erts/doc/src/erl.xml +++ b/erts/doc/src/erl.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> @@ -524,7 +524,7 @@ <p>Calling <c>erlang:halt/1</c> with a string argument will still produce a crash dump.</p> </item> - <tag><c><![CDATA[+e Number]]></c></tag> + <tag><marker id="+e"><c><![CDATA[+e Number]]></c></marker></tag> <item> <p>Set max number of ETS tables.</p> </item> diff --git a/erts/doc/src/erl_dist_protocol.xml b/erts/doc/src/erl_dist_protocol.xml index 84f4be208d..890293d802 100644 --- a/erts/doc/src/erl_dist_protocol.xml +++ b/erts/doc/src/erl_dist_protocol.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="iso-8859-1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> diff --git a/erts/doc/src/erl_driver.xml b/erts/doc/src/erl_driver.xml index c055d1ca9e..b453a4861e 100644 --- a/erts/doc/src/erl_driver.xml +++ b/erts/doc/src/erl_driver.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE cref SYSTEM "cref.dtd"> <cref> diff --git a/erts/doc/src/erl_ext_dist.xml b/erts/doc/src/erl_ext_dist.xml index c6849f3326..f91ed78122 100644 --- a/erts/doc/src/erl_ext_dist.xml +++ b/erts/doc/src/erl_ext_dist.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="iso-8859-1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> @@ -1014,10 +1014,10 @@ </row> <tcaption></tcaption></table> <p> - This term represents a bitstring whose length in bits is not a - multiple of 8 (created using the bit syntax in R12B and later). + This term represents a bitstring whose length in bits does + not have to be a multiple of 8. The <c>Len</c> field is an unsigned 4 byte integer (big endian). - The <c>Bits</c> field is the number of bits that are used + The <c>Bits</c> field is the number of bits (1-8) that are used in the last byte in the data field, counting from the most significant bit towards the least significant. diff --git a/erts/doc/src/erl_nif.xml b/erts/doc/src/erl_nif.xml index 864b91946a..7ac8181d47 100644 --- a/erts/doc/src/erl_nif.xml +++ b/erts/doc/src/erl_nif.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE cref SYSTEM "cref.dtd"> <cref> @@ -330,6 +330,8 @@ ok <c>upgrade</c> will be called to initialize the library. <c>unload</c> is called to release the library. They are all described individually below.</p> + <p>If compiling a nif for static inclusion via --enable-static-nifs you + have to define STATIC_ERLANG_NIF before the ERL_NIF_INIT declaration.</p> </item> <tag><marker id="load"/>int (*load)(ErlNifEnv* env, void** priv_data, ERL_NIF_TERM load_info)</tag> diff --git a/erts/doc/src/erl_prim_loader.xml b/erts/doc/src/erl_prim_loader.xml index 9f5b3f385b..6751deda4d 100644 --- a/erts/doc/src/erl_prim_loader.xml +++ b/erts/doc/src/erl_prim_loader.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> - <year>1996</year><year>2011</year> + <year>1996</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index a9642be6fa..711473afd2 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> @@ -2592,7 +2592,7 @@ os_prompt% </pre> fails, a <c>nodedown</c> message is delivered.</p> <p>Nodes connected through hidden connections can be monitored as any other node.</p> - <p>Failure: <c>badarg</c>if the local node is not alive.</p> + <p>Failure: <c>badarg</c> if the local node is not alive.</p> </desc> </func> <func> @@ -2738,7 +2738,28 @@ os_prompt% </pre> <desc> <p>Returns a port identifier as the result of opening a new Erlang port. A port can be seen as an external Erlang - process. <c><anno>PortName</anno></c> is one of the following:</p> + process. + </p> + <p>The name of the executable as well as the arguments + given in <c>cd</c>, <c>env</c>, <c>args</c> and <c>arg0</c> is subject to + Unicode file name translation if the system is running + in Unicode file name mode. To avoid + translation or force i.e. UTF-8, supply the executable + and/or arguments as a binary in the correct + encoding. See the <seealso + marker="kernel:file">file</seealso> module, the + <seealso marker="kernel:file#native_name_encoding/0"> + file:native_name_encoding/0</seealso> function and the + <seealso marker="stdlib:unicode_usage">stdlib users guide + </seealso> for details.</p> + + <note><p>The characters in the name (if given as a list) + can only be > 255 if the Erlang VM is started in + Unicode file name translation mode, otherwise the name + of the executable is limited to the ISO-latin-1 + character set.</p></note> + + <p><c><anno>PortName</anno></c> is one of the following:</p> <taglist> <tag><c>{spawn, <anno>Command</anno>}</c></tag> <item> @@ -2793,25 +2814,6 @@ os_prompt% </pre> executed, the appropriate command interpreter will implicitly be invoked, but there will still be no command argument expansion or implicit PATH search.</p> - - <p>The name of the executable as well as the arguments - given in <c>args</c> and <c>arg0</c> is subject to - Unicode file name translation if the system is running - in Unicode file name mode. To avoid - translation or force i.e. UTF-8, supply the executable - and/or arguments as a binary in the correct - encoding. See the <seealso - marker="kernel:file">file</seealso> module, the - <seealso marker="kernel:file#native_name_encoding/0"> - file:native_name_encoding/0</seealso> function and the - <seealso marker="stdlib:unicode_usage">stdlib users guide - </seealso> for details.</p> - - <note><p>The characters in the name (if given as a list) - can only be > 255 if the Erlang VM is started in - Unicode file name translation mode, otherwise the name - of the executable is limited to the ISO-latin-1 - character set.</p></note> <p>If the <c><anno>FileName</anno></c> cannot be run, an error exception, with the posix error code as the reason, is @@ -2887,11 +2889,7 @@ os_prompt% </pre> strings. The one exception is <c><anno>Val</anno></c> being the atom <c>false</c> (in analogy with <c>os:getenv/1</c>), which removes the environment variable. - </p> - <p>If Unicode filename encoding is in effect (see the <seealso - marker="erts:erl#file_name_encoding">erl manual - page</seealso>), the strings (both <c>Name</c> and - <c>Value</c>) may contain characters with codepoints > 255.</p> + </p> </item> <tag><c>{args, [ string() | binary() ]}</c></tag> <item> @@ -2919,21 +2917,6 @@ os_prompt% </pre> should not be given in this list. The proper executable name will automatically be used as argv[0] where applicable.</p> - <p>When the Erlang VM is running in Unicode file name - mode, the arguments can contain any Unicode characters and - will be translated into whatever is appropriate on the - underlying OS, which means UTF-8 for all platforms except - Windows, which has other (more transparent) ways of - dealing with Unicode arguments to programs. To avoid - Unicode translation of arguments, they can be supplied as - binaries in whatever encoding is deemed appropriate.</p> - - <note><p>The characters in the arguments (if given as a - list of characters) can only be > 255 if the Erlang - VM is started in Unicode file name mode, - otherwise the arguments are limited to the - ISO-latin-1 character set.</p></note> - <p>If one, for any reason, wants to explicitly set the program name in the argument vector, the <c>arg0</c> option can be used.</p> @@ -2949,9 +2932,6 @@ os_prompt% </pre> responds to this is highly system dependent and no specific effect is guaranteed.</p> - <p>The unicode file name translation rules of the - <c>args</c> option apply to this option as well.</p> - </item> <tag><c>exit_status</c></tag> @@ -3157,7 +3137,10 @@ os_prompt% </pre> (see below), being synchronous, and that the port does <em>not</em> reply with <c>{Port, closed}</c>. Any process may close a port with <c>port_close/1</c>, not only the port owner - (the connected process).</p> + (the connected process). If the calling process is linked to + port identified by <c><anno>Port</anno></c>, an exit signal due + to that link will be received by the process prior to the return + from <c>port_close/1</c>.</p> <p>For comparison: <c><anno>Port</anno> ! {self(), close}</c> fails with <c>badarg</c> if <c><anno>Port</anno></c> cannot be sent to (i.e., <c><anno>Port</anno></c> refers neither to a port nor to a process). If @@ -3166,6 +3149,7 @@ os_prompt% </pre> the port replies with <c>{Port, closed}</c> when all buffers have been flushed and the port really closes, but if the calling process is not the port owner the <em>port owner</em> fails with <c>badsig</c>.</p> + <p>Note that any process can close a port using <c><anno>Port</anno> ! {PortOwner, close}</c> just as if it itself was the port owner, but the reply always goes to the port owner.</p> @@ -3175,8 +3159,17 @@ os_prompt% </pre> implementation has been synchronous. <c>port_close/1</c> is however still fully synchronous. This due to its error behavior.</p> - <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not an open port or - the registered name of an open port.</p> + <p>Failure:</p> + <taglist> + <tag><c>badarg</c></tag> + <item> + If <c><anno>Port</anno></c> is not an identifier of an open + port, or the registered name of an open port. If the calling + process was linked to the previously open port identified by + <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to this exception. + </item> + </taglist> </desc> </func> <func> @@ -3211,8 +3204,11 @@ os_prompt% </pre> <taglist> <tag><c>badarg</c></tag> <item> - If <c><anno>Port</anno></c> is not an open port or the registered name - of an open port. + If <c><anno>Port</anno></c> is not an identifier of an open + port, or the registered name of an open port. If the calling + process was linked to the previously open port identified by + <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to this exception. </item> <tag><c>badarg</c></tag> <item> @@ -3255,8 +3251,11 @@ os_prompt% </pre> <taglist> <tag><c>badarg</c></tag> <item> - If <c><anno>Port</anno></c> is not an open port or the registered name - of an open port. + If <c><anno>Port</anno></c> is not an identifier of an open + port, or the registered name of an open port. If the calling + process was linked to the previously open port identified by + <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to this exception. </item> <tag><c>badarg</c></tag> <item> @@ -3323,9 +3322,20 @@ os_prompt% </pre> implementation has been synchronous. <c>port_connect/2</c> is however still fully synchronous. This due to its error behavior.</p> - <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not an open port - or the registered name of an open port, or if <c>Pid</c> is - not an existing local pid.</p> + <p>Failures:</p> + <taglist> + <tag><c>badarg</c></tag> + <item> + If <c><anno>Port</anno></c> is not an identifier of an open + port, or the registered name of an open port. If the calling + process was linked to the previously open port identified by + <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to this exception. + </item> + <tag><c>badarg</c></tag> + <item>If process identified by <c>Pid</c> is not an existing + local process.</item> + </taglist> </desc> </func> <func> @@ -3361,12 +3371,33 @@ os_prompt% </pre> binary term format and sent to the port.</p> <p>Returns: a term from the driver. The meaning of the returned data also depends on the port driver.</p> - <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not an open port or - the registered name of an open port, if <c><anno>Operation</anno></c> - cannot fit in a 32-bit integer, if the port driver does not - support synchronous control operations, or if the port driver - so decides for any reason (probably something wrong with - <c><anno>Operation</anno></c> or <c><anno>Data</anno></c>).</p> + <p>Failures:</p> + <taglist> + <tag><c>badarg</c></tag> + <item> + If <c><anno>Port</anno></c> is not an identifier of an open + port, or the registered name of an open port. If the calling + process was linked to the previously open port identified by + <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to this exception. + </item> + <tag><c>badarg</c></tag> + <item> + If <c><anno>Operation</anno></c> does not fit in a + 32-bit integer. + </item> + <tag><c>badarg</c></tag> + <item> + If the port driver does not support synchronous control + operations. + </item> + <tag><c>badarg</c></tag> + <item> + If the port driver so decides for any reason (probably + something wrong with <c><anno>Operation</anno></c>, or + <c><anno>Data</anno></c>). + </item> + </taglist> </desc> </func> <func> @@ -3376,7 +3407,12 @@ os_prompt% </pre> <p>Returns a list containing tuples with information about the <c><anno>Port</anno></c>, or <c>undefined</c> if the port is not open. The order of the tuples is not defined, nor are all the - tuples mandatory.</p> + tuples mandatory. + If <c>undefined</c> is returned and the calling process + was linked to a previously open port identified by + <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/1</c>.</p> <p>Currently the result will containt information about the following <c>Item</c>s: <c>registered_name</c> (if the port has a registered name), <c>id</c>, <c>connected</c>, <c>links</c>, @@ -3394,7 +3430,11 @@ os_prompt% </pre> <p><c><anno>Pid</anno></c> is the process identifier of the process connected to the port.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3406,7 +3446,11 @@ os_prompt% </pre> <p><c><anno>Index</anno></c> is the internal index of the port. This index may be used to separate ports.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3418,7 +3462,11 @@ os_prompt% </pre> <p><c><anno>Bytes</anno></c> is the total number of bytes read from the port.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3430,7 +3478,11 @@ os_prompt% </pre> <p><c><anno>Pids</anno></c> is a list of the process identifiers of the processes that the port is linked to.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3445,7 +3497,11 @@ os_prompt% </pre> that these results are highly implementation specific and might change in the future.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3459,7 +3515,11 @@ os_prompt% </pre> that the port itself might have allocated memory which is not included in <c><anno>Bytes</anno></c>.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3471,7 +3531,11 @@ os_prompt% </pre> <p><c><anno>Monitors</anno></c> represent processes that this port is monitoring.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3483,7 +3547,11 @@ os_prompt% </pre> <p><c><anno>Name</anno></c> is the command name set by <seealso marker="#open_port/2">open_port/2</seealso>.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3498,7 +3566,11 @@ os_prompt% </pre> Command}, Options)</seealso>. If the port is not the result of spawning an OS process, the value is <c>undefined</c>.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3514,7 +3586,11 @@ os_prompt% </pre> or <c><anno>Port</anno> ! {Owner, {command, Data}</c>. </p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3537,7 +3613,11 @@ os_prompt% </pre> in bytes, queued by the port using the ERTS driver queue implementation.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -3549,7 +3629,11 @@ os_prompt% </pre> <p><c><anno>RegisteredName</anno></c> is the registered name of the port. If the port has no registered name, <c>[]</c> is returned.</p> <p>If the port identified by <c><anno>Port</anno></c> is not open, - <c>undefined</c> is returned.</p> + <c>undefined</c> is returned. If <c>undefined</c> is returned and + the calling process was linked to a previously open port identified + by <c><anno>Port</anno></c>, an exit signal due to this link + was received by the process prior to the return from + <c>port_info/2</c>.</p> <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local port identifier, or an atom.</p> </desc> @@ -4852,8 +4936,8 @@ true</pre> <name name="statistics" arity="1" clause_i="6"/> <fsummary>Information about the run-queue</fsummary> <desc> - <p>Returns the length of the run queue, that is, the number - of processes that are ready to run.</p> + <p>Returns the total length of the run queues, that is, the number + of processes that are ready to run on all available run queues.</p> </desc> </func> <func> @@ -5441,7 +5525,11 @@ ok As of erts version 5.6.1 the return value is a list of <c>{instance, InstanceNo, InstanceInfo}</c> tuples where <c>InstanceInfo</c> contains information about - a specific instance of the allocator. + a specific instance of the allocator. As of erts version + 5.10.4 the returned list when calling + <c>erlang:system_info({allocator, mseg_alloc})</c> also + include an <c>{erts_mmap, _}</c> tuple as one element + in the list. If <c><anno>Alloc</anno></c> is not a recognized allocator, <c>undefined</c> is returned. If <c><anno>Alloc</anno></c> is disabled, <c>false</c> is returned.</p> @@ -5625,6 +5713,9 @@ ok <name name="system_info" arity="1" clause_i="49"/> <name name="system_info" arity="1" clause_i="50"/> <name name="system_info" arity="1" clause_i="51"/> + <name name="system_info" arity="1" clause_i="52"/> + <name name="system_info" arity="1" clause_i="53"/> + <name name="system_info" arity="1" clause_i="54"/> <fsummary>Information about the system</fsummary> <desc> <p>Returns various information about the current system @@ -5701,6 +5792,13 @@ ok information see the <seealso marker="erts:crash_dump">"How to interpret the Erlang crash dumps"</seealso> chapter in the ERTS User's Guide.</p> </item> + <tag><marker id="system_info_dist_buf_busy_limit"><c>dist_buf_busy_limit</c></marker></tag> + <item> + <p>Returns the value of the distribution buffer busy limit + in bytes. This limit can be set on startup by passing the + <seealso marker="erts:erl#+zdbbl">+zdbbl</seealso> command line + flag to <c>erl</c>.</p> + </item> <tag><c>dist_ctrl</c></tag> <item> <p>Returns a list of tuples @@ -5747,12 +5845,14 @@ ok The return value will always be <c>false</c> since the elib_malloc allocator has been removed.</p> </item> - <tag><marker id="system_info_dist_buf_busy_limit"><c>dist_buf_busy_limit</c></marker></tag> + <tag><c>ets_limit</c></tag> <item> - <p>Returns the value of the distribution buffer busy limit - in bytes. This limit can be set on startup by passing the - <seealso marker="erts:erl#+zdbbl">+zdbbl</seealso> command line - flag to <c>erl</c>.</p> + <p>Returns the maximum number of ETS tables allowed. This limit + can be increased on startup by passing the <seealso + marker="erts:erl#+e">+e</seealso> command line flag to + <c>erl</c> or by setting the environment variable + <c>ERL_MAX_ETS_TABLES</c> before starting the Erlang runtime + system.</p> </item> <tag><c>fullsweep_after</c></tag> <item> diff --git a/erts/doc/src/erlc.xml b/erts/doc/src/erlc.xml index 81dffe45cf..10cab344b0 100644 --- a/erts/doc/src/erlc.xml +++ b/erts/doc/src/erlc.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1997</year><year>2012</year> + <year>1997</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/erlsrv.xml b/erts/doc/src/erlsrv.xml index 365ae21d39..71cee714a5 100644 --- a/erts/doc/src/erlsrv.xml +++ b/erts/doc/src/erlsrv.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1998</year><year>2012</year> + <year>1998</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/erts_alloc.xml b/erts/doc/src/erts_alloc.xml index 6ce2261430..fffa9f594c 100644 --- a/erts/doc/src/erts_alloc.xml +++ b/erts/doc/src/erts_alloc.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE cref SYSTEM "cref.dtd"> <cref> @@ -271,6 +271,77 @@ memory segment cache is not reused if its size exceeds the requested size with more than relative max cache bad fit percent of the requested size. Default value is 20.</item> + <tag><marker id="MMsco"><c><![CDATA[+MMsco true|false]]></c></marker></tag> + <item> + Set <seealso marker="#MMscs">super carrier</seealso> only flag. This + flag defaults to <c>true</c>. When a super carrier is used and this + flag is <c>true</c>, <c>mseg_alloc</c> will only create carriers + in the super carrier. Note that the <c>alloc_util</c> framework may + create <c>sys_alloc</c> carriers, so if you want all carriers to + be created in the super carrier, you therefore want to disable use + of <c>sys_alloc</c> carriers by also passing + <seealso marker="#Musac"><c>+Musac false</c></seealso>. When the flag + is <c>false</c>, <c>mseg_alloc</c> will try to create carriers outside + of the super carrier when the super carrier is full. + <br/><br/> + <em>NOTE</em>: Setting this flag to <c>false</c> may not be supported + on all systems. This flag will in that case be ignored. + <br/><br/> + <em>NOTE</em>: The super carrier cannot be enabled nor + disabled on halfword heap systems. This flag will be + ignored on halfword heap systems. + </item> + <tag><marker id="MMscrfsd"><c><![CDATA[+MMscrfsd <amount>]]></c></marker></tag> + <item> + Set <seealso marker="#MMscs">super carrier</seealso> reserved + free segment descriptors. This parameter defaults to <c>65536</c>. + This parameter determines the amount of memory to reserve for + free segment descriptors used by the super carrier. If the system + runs out of reserved memory for free segment descriptors, other + memory will be used. This may however cause fragmentation issues, + so you want to ensure that this never happens. The maximum amount + of free segment descriptors used can be retrieved from the + <c>erts_mmap</c> tuple part of the result from calling + <seealso marker="erts:erlang#system_info_allocator_tuple">erlang:system_info({allocator, mseg_alloc})</seealso>. + </item> + <tag><marker id="MMscrpm"><c><![CDATA[+MMscrpm true|false]]></c></marker></tag> + <item> + Set <seealso marker="#MMscs">super carrier</seealso> reserve physical + memory flag. This flag defaults to <c>true</c>. When this flag is + <c>true</c>, physical memory will be reserved for the whole super + carrier at once when it is created. The reservation will after that + be left unchanged. When this flag is set to <c>false</c> only virtual + address space will be reserved for the super carrier upon creation. + The system will attempt to reserve physical memory upon carrier + creations in the super carrier, and attempt to unreserve physical + memory upon carrier destructions in the super carrier. + <br/><br/> + <em>NOTE</em>: What reservation of physical memory actually means + highly depends on the operating system, and how it is configured. For + example, different memory overcommit settings on Linux drastically + change the behaviour. Also note, setting this flag to <c>false</c> + may not be supported on all systems. This flag will in that case + be ignored. + <br/><br/> + <em>NOTE</em>: The super carrier cannot be enabled nor + disabled on halfword heap systems. This flag will be + ignored on halfword heap systems. + </item> + <tag><marker id="MMscs"><c><![CDATA[+MMscs <size in MB>]]></c></marker></tag> + <item> + Set super carrier size (in MB). The super carrier size defaults to + zero; i.e, the super carrier is by default disabled. The super + carrier is a large continuous area in the virtual address space. + <c>mseg_alloc</c> will always try to create new carriers in the super + carrier if it exists. Note that the <c>alloc_util</c> framework may + create <c>sys_alloc</c> carriers. For more information on this, see the + documentation of the <seealso marker="#MMsco"><c>+MMsco</c></seealso> + flag. + <br/><br/> + <em>NOTE</em>: The super carrier cannot be enabled nor + disabled on halfword heap systems. This flag will be + ignored on halfword heap systems. + </item> <tag><marker id="MMmcs"><c><![CDATA[+MMmcs <amount>]]></c></marker></tag> <item> Max cached segments. The maximum number of memory segments @@ -490,6 +561,11 @@ placed in separate memory segments. When this limit has been reached, new carriers will be placed in memory retrieved from <c>sys_alloc</c>.</item> + <tag><marker id="Musac"><c><![CDATA[+Musac <bool>]]></c></marker></tag> + <item> + Allow <c>sys_alloc</c> carriers. By default <c>true</c>. If + set to <c>false</c>, <c>sys_alloc</c> carriers will never be + created by allocators using the <c>alloc_util</c> framework.</item> </taglist> <p>Instrumentation flags:</p> <taglist> @@ -545,6 +621,16 @@ </item> </taglist> </item> + <tag><marker id="Mlpm"><c>+Mlpm all|no</c></marker></tag> + <item>Lock physical memory. The default value is <c>no</c>, i.e., + no physical memory will be locked. If set to <c>all</c>, all + memory mappings made by the runtime system, will be locked into + physical memory. If set to <c>all</c>, the runtime system will fail + to start if this feature is not supported, the user has not got enough + privileges, or the user is not allowed to lock enough physical memory. + The runtime system will also fail with an out of memory condition + if the user limit on the amount of locked memory is reached. + </item> </taglist> <p>Only some default values have been presented here. diff --git a/erts/doc/src/escript.xml b/erts/doc/src/escript.xml index 9e2a87dde6..180447cac4 100644 --- a/erts/doc/src/escript.xml +++ b/erts/doc/src/escript.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> diff --git a/erts/doc/src/fascicules.xml b/erts/doc/src/fascicules.xml index cae197a516..1c371bd9c8 100644 --- a/erts/doc/src/fascicules.xml +++ b/erts/doc/src/fascicules.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE fascicules SYSTEM "fascicules.dtd"> <fascicules> diff --git a/erts/doc/src/inet_cfg.xml b/erts/doc/src/inet_cfg.xml index 2a033c037c..d40bc5f9ee 100644 --- a/erts/doc/src/inet_cfg.xml +++ b/erts/doc/src/inet_cfg.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> - <year>2004</year><year>2010</year> + <year>2004</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/init.xml b/erts/doc/src/init.xml index d5c43f6e57..09b5493341 100644 --- a/erts/doc/src/init.xml +++ b/erts/doc/src/init.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> - <year>1996</year><year>2011</year> + <year>1996</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/match_spec.xml b/erts/doc/src/match_spec.xml index bdcf9c3816..334b47d34c 100644 --- a/erts/doc/src/match_spec.xml +++ b/erts/doc/src/match_spec.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> - <year>1999</year><year>2012</year> + <year>1999</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/notes.xml b/erts/doc/src/notes.xml index 77ffeefd04..b25e4ccbec 100644 --- a/erts/doc/src/notes.xml +++ b/erts/doc/src/notes.xml @@ -30,6 +30,30 @@ </header> <p>This document describes the changes made to the ERTS application.</p> +<section><title>Erts 5.10.3.1</title> + + <section><title>Improvements and New Features</title> + <list> + <item> + <p> + Memory allocators will be able to create <c>sys_alloc</c> + carriers as fallback, if <c>mseg_alloc</c> cannot create + more carriers, on systems with <c>posix_memalign()</c> + support. This is similar to how it worked in pre-R16 + releases.</p> + <p> + Windows systems will create carriers using + <c>_aligned_malloc()</c> and can by this use the new + optimized allocator header scheme introduced in R16 on + other platforms.</p> + <p> + Own Id: OTP-11318</p> + </item> + </list> + </section> + +</section> + <section><title>Erts 5.10.3</title> <section><title>Fixed Bugs and Malfunctions</title> diff --git a/erts/doc/src/notes_history.xml b/erts/doc/src/notes_history.xml index cc3b938c86..4420311912 100644 --- a/erts/doc/src/notes_history.xml +++ b/erts/doc/src/notes_history.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> - <year>2006</year><year>2009</year> + <year>2006</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/part.xml b/erts/doc/src/part.xml index fa50329cad..7b17b5b551 100644 --- a/erts/doc/src/part.xml +++ b/erts/doc/src/part.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE part SYSTEM "part.dtd"> <part xmlns:xi="http://www.w3.org/2001/XInclude"> @@ -32,6 +32,7 @@ <p>The Erlang Runtime System Application <em>ERTS</em>.</p> </description> <xi:include href="communication.xml"/> + <xi:include href="time_correction.xml"/> <xi:include href="match_spec.xml"/> <xi:include href="crash_dump.xml"/> <xi:include href="alt_dist.xml"/> diff --git a/erts/doc/src/part_notes.xml b/erts/doc/src/part_notes.xml index 4f183999e6..b5c8f0af09 100644 --- a/erts/doc/src/part_notes.xml +++ b/erts/doc/src/part_notes.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE part SYSTEM "part.dtd"> <part xmlns:xi="http://www.w3.org/2001/XInclude"> <header> <copyright> - <year>2004</year><year>2009</year> + <year>2004</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/part_notes_history.xml b/erts/doc/src/part_notes_history.xml index 1b9bcca773..a99fa4a17f 100644 --- a/erts/doc/src/part_notes_history.xml +++ b/erts/doc/src/part_notes_history.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE part SYSTEM "part.dtd"> <part xmlns:xi="http://www.w3.org/2001/XInclude"> <header> <copyright> - <year>2006</year><year>2009</year> + <year>2006</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/ref_man.xml b/erts/doc/src/ref_man.xml index e55923c344..8ed7090a61 100644 --- a/erts/doc/src/ref_man.xml +++ b/erts/doc/src/ref_man.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE application SYSTEM "application.dtd"> <application xmlns:xi="http://www.w3.org/2001/XInclude"> diff --git a/erts/doc/src/run_erl.xml b/erts/doc/src/run_erl.xml index c9784299b3..684f7b1ddd 100644 --- a/erts/doc/src/run_erl.xml +++ b/erts/doc/src/run_erl.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1999</year><year>2011</year> + <year>1999</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/specs.xml b/erts/doc/src/specs.xml index e5c2f4783f..41a3984659 100644 --- a/erts/doc/src/specs.xml +++ b/erts/doc/src/specs.xml @@ -1,4 +1,4 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <specs xmlns:xi="http://www.w3.org/2001/XInclude"> <xi:include href="../specs/specs_erl_prim_loader.xml"/> <xi:include href="../specs/specs_erlang.xml"/> diff --git a/erts/doc/src/start.xml b/erts/doc/src/start.xml index 5dc33deb2a..e9a5714f93 100644 --- a/erts/doc/src/start.xml +++ b/erts/doc/src/start.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1999</year><year>2009</year> + <year>1999</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/start_erl.xml b/erts/doc/src/start_erl.xml index 92d87b095a..fe808f7737 100644 --- a/erts/doc/src/start_erl.xml +++ b/erts/doc/src/start_erl.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1998</year><year>2011</year> + <year>1998</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/time_correction.xml b/erts/doc/src/time_correction.xml new file mode 100644 index 0000000000..d52cc7f3e2 --- /dev/null +++ b/erts/doc/src/time_correction.xml @@ -0,0 +1,274 @@ +<?xml version="1.0" encoding="utf8" ?> +<!DOCTYPE chapter SYSTEM "chapter.dtd"> + +<chapter> + <header> + <copyright> + <year>1999</year><year>2013</year> + <holder>Ericsson AB. All Rights Reserved.</holder> + </copyright> + <legalnotice> + The contents of this file are subject to the Erlang Public License, + Version 1.1, (the "License"); you may not use this file except in + compliance with the License. You should have received a copy of the + Erlang Public License along with this software. If not, it can be + retrieved online at http://www.erlang.org/. + + Software distributed under the License is distributed on an "AS IS" + basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See + the License for the specific language governing rights and limitations + under the License. + + </legalnotice> + + <title>Time and time correction in Erlang</title> + <prepared>Patrik Nyblom</prepared> + <responsible></responsible> + <docno></docno> + <approved></approved> + <checked></checked> + <date>2013-08-28</date> + <rev>PA1</rev> + <file>time_correction.xml</file> + </header> + <p>Time is vital to an Erlang program and, more importantly, <em>correct</em> + time is vital to an Erlang program. As Erlang is a language with + soft real time properties and we have the possibility to express + time in our programs, the Virtual Machine and the language has to be + very careful about what is considered a correct point in time and in + how time functions behave.</p> + + <p>In the beginning, Erlang was constructed assuming that the wall + clock time in the system showed a monotonic time moving forward at + exactly the same pace as the definition of time. That more or less + meant that an atomic clock (or better) was expected to be attached + to your hardware and that the hardware was then expected to be + locked away from any human (or unearthly) tinkering for all + eternity. While this might be a compelling thought, it's simply + never the case.</p> + + <p>A "normal" modern computer can not keep time. Not on itself and + not unless you actually have a chip level atomic clock wired to + it. Time, as perceived by your computer, will normally need to be + corrected. Hence the NTP protocol that together with the ntpd + process will do it's best to keep your computers time in sync with + the "real" time in the universe. Between NTP corrections, usually a + less potent time-keeper than an atomic clock is used.</p> + + <p>But NTP is not fail safe. The NTP server can be unavailable, the + ntp.conf can be wrongly configured or your computer may from time to + time be disconnected from the internet. Furthermore you can have a + user (or even system administrator) on your system that thinks the + right way to handle daylight saving time is to adjust the clock one + hour two times a year (a tip, that is not the right way to do + it...). To further complicate things, this user fetched your + software from the internet and has never ever thought about what's + the correct time as perceived by a computer. The user simply does + not care about keeping the wall clock in sync with the rest of the + universe. The user expects your program to have omnipotent knowledge + about the time.</p> + + <p>Most programmers also expect time to be reliable, at least until + they realize that the wall clock time on their workstation is of by + a minute. Then they simply set it to the correct time, maybe or + maybe not in a smooth way. Most probably not in a smooth way.</p> + + <p>The amount of problems that arise when you expect the wall clock + time on the system to always be correct may be immense. Therefore Erlang + introduced the "corrected estimate of time", or the "time + correction" many years ago. The time correction relies on the fact + that most operating systems have some kind of monotonic clock, + either a real time extension or some built in "tick counter" that is + independent of the wall clock settings. This counter may have + microsecond resolution or much less, but generally it has a drift + that is not to be ignored.</p> + + <p>So we have this monotonic ticking and we have the wall clock + time. Two unreliable times that together can give us an estimate of + an actual wall clock time that does not jump around and that + monotonically moves forward. If the tick counter has a high + resolution, this is fairly easy to do, if the counter has a low + resolution, it's more expensive, but still doable down to + frequencies of 50-60 Hz (of the tick counter).</p> + + <p>So the corrected time is the nearest approximation of an atomic + clock that is available on the computer. We want it to have the + following properties:</p> + <taglist> + <tag>Monotonic</tag> + <item>The clock should not move backwards</item> + <tag>Intervals should be near the truth</tag> + <item>We want the actual time (as measured by an atomic clock or + an astronomer) that passes between two time stamps, T1 and T2, to be as + near to T2 - T1 as possible.</item> + <tag>Tight coupling to the wall clock</tag> + <item>We want a timer that is to be fired when the wall clock + reaches a time in the future, to fire as near to that point in + time as possible</item> + </taglist> + <p>To meet all the criteria, we have to utilize both times in such a + way that Erlangs "corrected time" moves slightly slower or slightly + faster than the wall clock to get in sync with it. The word + "slightly" means a maximum of 1% difference to the wall clock time, + meaning that a sudden change in the wall clock of one minute, takes + 100 minutes to fix, by letting all "corrected time" move 1% slower + or faster.</p> + + <p>Needless to say, correcting for a faulty handling of daylight + saving time may be disturbing to a user comparing wall clock + time to for example calendar:now_to_local_time(erlang:now()). But + calendar:now_to_local_time/1 is not supposed to be used for presenting wall + clock time to the user.</p> + + <p>Time correction is not perfect, but it saves you from the havoc + of clocks jumping around, which would make timers in your program + fire far to late or far to early and could bring your whole system + to it's knees (or worse) just because someone detected a small error + in the wall clock time of the server where your program runs. So + while it might be confusing, it is still a really good feature of + Erlang and you should not throw it away using time functions which + may give you higher benchmark results, not unless you really know + what you're doing.</p> + + <section> + <title>What does time correction mean in my system?</title> + <p>Time correction means that Erlang estimates a time from current + and previous settings of the wall clock, and it uses a fairly + exact tick counter to detect when the wall clock time has jumped + for some reason, slowly adjusting to the new value.</p> + + <p>In practice, this means that the difference between two calls + to time corrected functions, like erlang:now(), might differ up to + one percent from the corresponding calls to non time corrected + functions (like os:timestamp()). Furthermore, if comparing + calendar:local_time/0 to calendar:now_to_local_time(erlang:now()), + you might temporarily see a difference, depending on how well kept your + system is.</p> + + <p>It is important to understand that it is (to the program) + always unknown if it is the wall clock time that moves in the + wrong pace or the Erlang corrected time. The only way to determine + that, is to have an external source of universally correct time. If + some such source is available, the wall clock time can be kept + nearly perfect at all times, and no significant difference will be + detected between erlang:now/0's pace and the wall clock's.</p> + + <p>Still, the time correction will mean that your system keeps + it's real time characteristics very well, even when the wall clock + is unreliable.</p> + </section> + <section> + <title>Where does Erlang use corrected time?</title> + <p>For all functionality where real time characteristics are + desirable, time correction is used. This basically means:</p> + <taglist> + <tag>erlang:now/0</tag> + <item>The infamous erlang:now/0 function uses time correction so + that differences between two "now-timestamps" will correspond to + other timeouts in the system. erlang:now/0 also holds other + properties, discussed later.</item> + <tag>receive ... after</tag> + <item>Timeouts on receive uses time correction to determine a + stable timeout interval.</item> + <tag>The timer module</tag> + <item>As the timer module uses other built in functions which + deliver corrected time, the timer module itself works with + corrected time.</item> + <tag>erlang:start_timer/3 and erlang:send_after/3</tag> + <item>The timer BIF's work with corrected time, so that they + will not fire prematurely or too late due to changes in the wall + clock time.</item> + </taglist> + + <p>All other functionality in the system where erlang:now/0 or any + other time corrected functionality is used, will of course + automatically benefit from it, as long as it's not "optimized" to + use some other time stamp function (like os:timestamp/0).</p> + + <p>Modules like calendar and functions like erlang:localtime/0 use + the wall clock time as it is currently set on the system. They + will not use corrected time. However, if you use a now-value and + convert it to local time, you will get a corrected local time + value, which may or may not be what you want. Typically older code + tend to use erlang:now/0 as a wall clock time, which is usually + correct (at least when testing), but might surprise you when + compared to other times in the system.</p> + </section> + <section> + <title>What is erlang:now/0 really?</title> + <p>erlang:now/0 is a function designed to serve multiple purposes + (or a multi-headed beast if you're a VM designer). It is expected + to hold the following properties:</p> + <taglist> + <tag>Monotonic</tag> + <item>erlang:now() never jumps backwards - it always moves + forward</item> + <tag>Interval correct</tag> + <item>The interval between two erlang:now() calls is expected to + correspond to the correct time in real life (as defined by an + atomic clock, or better)</item> + <tag>Absolute correctness</tag> + <item>The erlang:now/0 value should be possible to convert to an + absolute and correct date-time, corresponding to the real world + date and time (the wall clock)</item> + <tag>System correspondence</tag> + <item>The erlang:now/0 value converted to a date-time is + expected to correspond to times given by other programs on the + system (or by functions like os:timestamp/0)</item> + <tag>Unique</tag> + <item>No two calls to erlang:now on one Erlang node should + return the same value</item> + </taglist> + <p>All these requirements are possible to uphold at the same + time if (and only if):</p> + <taglist> + <tag>The wall clock time of the system is perfect</tag> + <item>The system (Operating System) time needs to be perfectly + in sync with the actual time as defined by an atomic clock or + a better time source. A good installation using NTP, and that is + up to date before Erlang starts, will have properties that for + most users and programs will be near indistinguishable from the + perfect time. Note that any larger corrections to the time done + by hand, or after Erlang has started, will partly (or + temporarily) invalidate some of the properties, as the time is + no longer perfect.</item> + <tag>Less than one call per microsecond to erlang:now/0 is + done</tag> + <item>This means that at <em>any</em> microsecond interval in + time, there can be no more than one call to erlang:now/0 in the + system. However, for the system not to loose it's properties + completely, it's enough that it on average is no more than one + call per microsecond (in one Erlang node).</item> + </taglist> + <p>The uniqueness property of erlang:now/0 is the most limiting + property. It means that erlang:now() maintains a global state and + that there is a hard-to-check property of the system that needs to + be maintained. For most applications this is still not a problem, + but a future system might very well manage to violate the + frequency limit on the calls globally. The uniqueness property is + also quite useless, as there are globally unique references that + provide a much better unique value to programs. However the + property will need to be maintained unless a really subtle + backward compatibility issue is to be introduced.</p> + </section> + <section> + <title>Should I use erlang:now/0 or os:timestamp/0</title> + <p>The simple answer is to use erlang:now/0 for everything where + you want to keep real time characteristics, but use os:timestamp + for things like logs, user communication and debugging (typically + timer:ts uses os:timestamp, as it is a test tool, not a real world + application API). The benefit of using os:timestamp/0 is that it's + faster and does not involve any global state (unless the operating + system has one). The downside is that it will be vulnerable to wall + clock time changes.</p> + </section> + <section> + <title>Turning off time correction</title> + <p>If, for some reason, time correction causes trouble and you are + absolutely confident that the wall clock on the system is nearly + perfect, you can turn off time correction completely by giving the + <c>+c</c> option to <c>erl</c>. The probability for this being a + good idea, is very low.</p> + </section> +</chapter> + diff --git a/erts/doc/src/tty.xml b/erts/doc/src/tty.xml index b16523e085..db15195f65 100644 --- a/erts/doc/src/tty.xml +++ b/erts/doc/src/tty.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE chapter SYSTEM "chapter.dtd"> <chapter> <header> <copyright> - <year>1996</year><year>2010</year> + <year>1996</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/werl.xml b/erts/doc/src/werl.xml index 1494d91da8..49cc45e745 100644 --- a/erts/doc/src/werl.xml +++ b/erts/doc/src/werl.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> - <year>1998</year><year>2009</year> + <year>1998</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> diff --git a/erts/doc/src/zlib.xml b/erts/doc/src/zlib.xml index 8917ab5c3a..afc597b729 100644 --- a/erts/doc/src/zlib.xml +++ b/erts/doc/src/zlib.xml @@ -1,10 +1,10 @@ -<?xml version="1.0" encoding="latin1" ?> +<?xml version="1.0" encoding="utf-8" ?> <!DOCTYPE erlref SYSTEM "erlref.dtd"> <erlref> <header> <copyright> - <year>2005</year><year>2011</year> + <year>2005</year><year>2013</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> |