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Diffstat (limited to 'erts/doc/src/erlang.xml')
| -rw-r--r-- | erts/doc/src/erlang.xml | 1207 |
1 files changed, 1026 insertions, 181 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index 0e5909a52d..3fea64cef5 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -58,7 +58,78 @@ </datatype> <datatype> <name name="timestamp"></name> - <desc><p>See <seealso marker="#now/0">now/0</seealso>.</p> + <desc><p>See <seealso marker="#timestamp/0">erlang:timestamp/0</seealso>.</p> + </desc> + </datatype> + <marker id="type_time_unit"/> + <datatype> + <name name="time_unit"></name> + <desc><p>Currently supported time unit representations:</p> + <taglist> + <tag><c>PartsPerSecond :: integer() >= 1</c></tag> + <item><p>Time unit expressed in parts per second. That is, + the time unit equals <c>1/PartsPerSecond</c> second.</p></item> + + <tag><c>seconds</c></tag> + <item><p>Symbolic representation of the time unit + represented by the integer <c>1</c>.</p></item> + + <tag><c>milli_seconds</c></tag> + <item><p>Symbolic representation of the time unit + represented by the integer <c>1000</c>.</p></item> + + <tag><c>micro_seconds</c></tag> + <item><p>Symbolic representation of the time unit + represented by the integer <c>1000000</c>.</p></item> + + <tag><c>nano_seconds</c></tag> + <item><p>Symbolic representation of the time unit + represented by the integer <c>1000000000</c>.</p></item> + + <tag><c>native</c></tag> + <item><p>Symbolic representation of the native time unit + used by the Erlang runtime system.</p> + + <p>The <c>native</c> time unit is determined at + runtime system start, and will remain the same until + the runtime system terminates. If a runtime system + is stopped and then started again (even on the same + machine), the <c>native</c> time unit of the new + runtime system instance may differ from the + <c>native</c> time unit of the old runtime system + instance.</p> + + <p>One can get an approximation of the <c>native</c> + time unit by calling <c>erlang:convert_time_unit(1, + seconds, native)</c>. The result equals the number + of whole <c>native</c> time units per second. In case + the number of <c>native</c> time units per second does + not add up to a whole number, the result will be + rounded downwards.</p> + + <note> + <p>The value of the <c>native</c> time unit gives + you more or less no information at all about the + quality of time values. It sets a limit for + the + <seealso marker="time_correction#Time_Resolution">resolution</seealso> + as well as for the + <seealso marker="time_correction#Time_Precision">precision</seealso> + of time values, + but it gives absolutely no information at all about the + <seealso marker="time_correction#Time_Accuracy">accuracy</seealso> + of time values. The resolution of the <c>native</c> time + unit and the resolution of time values may differ + significantly.</p> + </note> + </item> + + </taglist> + + <p>The <c>time_unit/0</c> type may be extended. Use + <seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit/3</c></seealso> + in order to convert time values between time units.</p> + </desc> </datatype> </datatypes> @@ -465,29 +536,108 @@ </desc> </func> <func> - <name name="cancel_timer" arity="1"/> + <name name="cancel_timer" arity="2"/> <fsummary>Cancel a timer</fsummary> <desc> - <p>Cancels a timer, where <c><anno>TimerRef</anno></c> was returned by - either - <seealso marker="#send_after/3">erlang:send_after/3</seealso> - or - <seealso marker="#start_timer/3">erlang:start_timer/3</seealso>. - If the timer is there to be removed, the function returns - the time in milliseconds left until the timer would have expired, - otherwise <c>false</c> (which means that <c><anno>TimerRef</anno></c> was - never a timer, that it has already been cancelled, or that it - has already delivered its message).</p> + <p> + Cancels a timer that has been created by either + <seealso marker="#start_timer/4"><c>erlang:start_timer()</c></seealso>, + or <seealso marker="#send_after/4"><c>erlang:send_after()</c></seealso>. + <c><anno>TimerRef</anno></c> identifies the timer, and + was returned by the BIF that created the timer. + </p> + <p>Currently available <c><anno>Option</anno></c>s:</p> + <taglist> + <tag><c>{async, Async}</c></tag> + <item> + <p> + Asynchronous request for cancellation. <c>Async</c> + defaults to <c>false</c> which will cause the + cancellation to be performed synchronously. When + <c>Async</c> is set to <c>true</c>, the cancel + operation will be performed asynchronously. That is, + <c>erlang:cancel_timer()</c> will send an asynchronous + request for cancellation to the timer service that + manages the timer, and then return <c>ok</c>. + </p> + </item> + <tag><c>{info, Info}</c></tag> + <item> + <p> + Request information about the <c><anno>Result</anno></c> + of the cancellation. <c>Info</c> defaults to <c>true</c> + which means that the <c><anno>Result</anno></c> will + be given. When <c>Info</c> is set to <c>false</c>, no + information about the result of the cancellation + will be given. When the operation is performed</p> + <taglist> + <tag>synchronously</tag> + <item> + <p> + If <c>Info</c> is <c>true</c>, the <c>Result</c> will + returned by <c>erlang:cancel_timer()</c>; otherwise, + <c>ok</c> will be returned. + </p> + </item> + <tag>asynchronously</tag> + <item> + <p> + If <c>Info</c> is <c>true</c>, a message on the form + <c>{cancel_timer, <anno>TimerRef</anno>, + <anno>Result</anno>}</c> will be sent to the + caller of <c>erlang:cancel_timer()</c> when the + cancellation operation has been performed; otherwise, + no message will be sent. + </p> + </item> + </taglist> + </item> + </taglist> + <p> + More <c><anno>Option</anno></c>s may be added in the future. + </p> + <p> + When the <c><anno>Result</anno></c> equals <c>false</c>, a + timer corresponding to <c><anno>TimerRef</anno></c> could not + be found. This can be either because the timer had expired, + already had been canceled, or because <c><anno>TimerRef</anno></c> + never has corresponded to a timer. If the timer has expired, + the timeout message has been sent, but it does not tell you + whether or not it has arrived at its destination yet. When the + <c><anno>Result</anno></c> is an integer, it represents the + time in milli-seconds left until the timer will expire. + </p> + <note> + <p> + The timer service that manages the timer may be co-located + with another scheduler than the scheduler that the calling + process is executing on. If this is the case, communication + with the timer service will take much longer time than if it + is located locally. If the calling process is in critical + path, and can do other things while waiting for the result + of this operation, or is not interested in the result of + the operation, you want to use the <c>{async, true}</c> + option. If using the <c>{async, false}</c> option, the calling + process will be blocked until the operation has been + performed. + </p> + </note> <p>See also - <seealso marker="#send_after/3">erlang:send_after/3</seealso>, - <seealso marker="#start_timer/3">erlang:start_timer/3</seealso>, + <seealso marker="#send_after/4"><c>erlang:send_after/4</c></seealso>, + <seealso marker="#start_timer/4"><c>erlang:start_timer/4</c></seealso>, and - <seealso marker="#read_timer/1">erlang:read_timer/1</seealso>.</p> - <p>Note: Cancelling a timer does not guarantee that the message - has not already been delivered to the message queue.</p> + <seealso marker="#read_timer/2"><c>erlang:read_timer/2</c></seealso>.</p> + </desc> + </func> + <func> + <name name="cancel_timer" arity="1"/> + <fsummary>Cancel a timer</fsummary> + <desc> + <p>Cancels a timer. The same as calling + <seealso marker="#cancel_timer/2"><c>erlang:cancel_timer(TimerRef, + [])</c></seealso>.</p> </desc> </func> - <func> <name name="check_old_code" arity="1"/> <fsummary>Check if a module has old code</fsummary> @@ -585,6 +735,22 @@ </desc> </func> <func> + <name name="convert_time_unit" arity="3"/> + <fsummary>Convert time unit of a time value</fsummary> + <desc> + <p>Converts the <c><anno>Time</anno></c> value of time unit + <c><anno>FromUnit</anno></c> to the corresponding + <c><anno>ConvertedTime</anno></c> value of time unit + <c><anno>ToUnit</anno></c>. The result is rounded + using the floor function.</p> + + <warning><p>You may lose accuracy and precision when converting + between time units. In order to minimize such loss, collect all + data at <c>native</c> time unit and do the conversion on the end + result.</p></warning> + </desc> + </func> + <func> <name name="crc32" arity="1"/> <fsummary>Compute crc32 (IEEE 802.3) checksum</fsummary> <desc> @@ -1252,10 +1418,11 @@ true <fsummary>Check if a function is exported and loaded</fsummary> <desc> <p>Returns <c>true</c> if the module <c><anno>Module</anno></c> is loaded - and contains an exported function <c><anno>Function</anno>/<anno>Arity</anno></c>; - otherwise <c>false</c>.</p> - <p>Returns <c>false</c> for any BIF (functions implemented in C - rather than in Erlang).</p> + and contains an exported function <c><anno>Function</anno>/<anno>Arity</anno></c>, + or if there is a BIF (a built-in function implemented in C) + with the given name; otherwise returns <c>false</c>.</p> + <note><p>This function used to return false for built-in + functions before the 18.0 release.</p></note> </desc> </func> <func> @@ -1376,6 +1543,19 @@ true </desc> </func> <func> + <name name="get_keys" arity="0"/> + <fsummary>Return a list of all keys from the process dictionary</fsummary> + <desc> + <p>Returns a list of keys all keys present in the process dictionary.</p> + <pre> +> <input>put(dog, {animal,1}),</input> +<input>put(cow, {animal,2}),</input> +<input>put(lamb, {animal,3}),</input> +<input>get_keys().</input> +[dog,cow,lamb]</pre> + </desc> + </func> + <func> <name name="get_keys" arity="1"/> <fsummary>Return a list of keys from the process dictionary</fsummary> <desc> @@ -2191,14 +2371,15 @@ os_prompt% </pre> </func> <func> <name name="make_ref" arity="0"/> - <fsummary>Return an almost unique reference</fsummary> + <fsummary>Return a unique reference</fsummary> <desc> - <p>Returns an almost unique reference.</p> - <p>The returned reference will re-occur after approximately 2^82 - calls; therefore it is unique enough for practical purposes.</p> - <pre> -> <input>make_ref().</input> -#Ref<0.0.0.135></pre> + <p>Return a <seealso marker="doc/efficiency_guide:advanced#unique_references">unique + reference</seealso>. The reference is unique among + connected nodes.</p> + <warning><p>Known issue: When a node is restarted multiple + times with the same node name, references created + on a newer node can be mistaken for a reference + created on an older node with the same node name.</p></warning> </desc> </func> <func> @@ -2499,97 +2680,178 @@ os_prompt% </pre> </desc> </func> <func> - <name name="monitor" arity="2"/> + <name name="monitor" arity="2" clause_i="1"/> + <name name="monitor" arity="2" clause_i="2"/> + <type name="registered_name"/> + <type name="registered_process_identifier"/> + <type name="monitor_process_identifier"/> <fsummary>Start monitoring</fsummary> <desc> - <p>The calling process starts monitoring <c><anno>Item</anno></c> which is - an object of type <c><anno>Type</anno></c>.</p> - <p>Currently only processes can be monitored, i.e. the only - allowed <c><anno>Type</anno></c> is <c>process</c>, but other types may be - allowed in the future.</p> - <p><c><anno>Item</anno></c> can be:</p> - <taglist> - <tag><c>pid()</c></tag> - <item> - <p>The pid of the process to monitor.</p> - </item> - <tag><c>{RegName, Node}</c></tag> - <item> - <p>A tuple consisting of a registered name of a process and - a node name. The process residing on the node <c>Node</c> - with the registered name <c>RegName</c> will be monitored.</p> - </item> - <tag><c>RegName</c></tag> - <item> - <p>The process locally registered as <c>RegName</c> will be - monitored.</p> - </item> - </taglist> - <note> - <p>When a process is monitored by registered name, the process - that has the registered name at the time when - <c>monitor/2</c> is called will be monitored. + <p>Send a monitor request of type <c><anno>Type</anno></c> to the + entity identified by <c><anno>Item</anno></c>. The caller of + <c>monitor/2</c> will later be notified by a monitor message on the + following format if the monitored state is changed:</p> + <code type="none">{Tag, <anno>MonitorRef</anno>, <anno>Type</anno>, Object, Info}</code> + <note><p>The monitor request is an asynchronous signal. That is, it + takes time before the signal reach its destination.</p></note> + <p>Currently valid <c><anno>Type</anno></c>s:</p> + <taglist> + <tag><marker id="monitor_process"/><c>process</c></tag> + <item> + <p>Monitor the existence of the process identified by + <c><anno>Item</anno></c>. Currently valid + <c><anno>Item</anno></c>s in combination with the + <c>process <anno>Type</anno></c>:</p> + <taglist> + <tag><c>pid()</c></tag> + <item> + <p>The process identifier of the process to monitor.</p> + </item> + <tag><c>{RegisteredName, Node}</c></tag> + <item> + <p>A tuple consisting of a registered name of a process and + a node name. The process residing on the node <c>Node</c> + with the registered name <c>{RegisteredName, Node}</c> will + be monitored.</p> + </item> + <tag><c>RegisteredName</c></tag> + <item> + <p>The process locally registered as <c>RegisteredName</c> + will become monitored.</p> + </item> + </taglist> + <note><p>When a process is monitored by registered name, the + process that has the registered name at the time when the + monitor request reach its destination will be monitored. The monitor will not be effected, if the registered name is - unregistered.</p> - </note> - <p>A <c>'DOWN'</c> message will be sent to the monitoring - process if <c><anno>Item</anno></c> dies, if <c><anno>Item</anno></c> does not exist, - or if the connection is lost to the node which <c><anno>Item</anno></c> - resides on. A <c>'DOWN'</c> message has the following pattern:</p> - <code type="none"> -{'DOWN', MonitorRef, Type, Object, Info}</code> - <p>where <c>MonitorRef</c> and <c>Type</c> are the same as - described above, and:</p> - <taglist> - <tag><c>Object</c></tag> - <item> - <p>A reference to the monitored object:</p> - <list type="bulleted"> - <item>the pid of the monitored process, if <c><anno>Item</anno></c> was - specified as a pid.</item> - <item><c>{RegName, Node}</c>, if <c><anno>Item</anno></c> was specified as - <c>{RegName, Node}</c>.</item> - <item><c>{RegName, Node}</c>, if <c><anno>Item</anno></c> was specified as - <c>RegName</c>. <c>Node</c> will in this case be the - name of the local node (<c>node()</c>).</item> - </list> - </item> - <tag><c>Info</c></tag> - <item> - <p>Either the exit reason of the process, <c>noproc</c> - (non-existing process), or <c>noconnection</c> (no - connection to <c><anno>Node</anno></c>).</p> - </item> - </taglist> - <note> - <p>If/when <c>monitor/2</c> is extended (e.g. to - handle other item types than <c>process</c>), other - possible values for <c>Object</c>, and <c>Info</c> in the - <c>'DOWN'</c> message will be introduced.</p> - </note> - <p>The monitoring is turned off either when the <c>'DOWN'</c> - message is sent, or when - <seealso marker="#demonitor/1">demonitor/1</seealso> - is called.</p> - <p>If an attempt is made to monitor a process on an older node - (where remote process monitoring is not implemented or one - where remote process monitoring by registered name is not - implemented), the call fails with <c>badarg</c>.</p> - <p>Making several calls to <c>monitor/2</c> for the same - <c><anno>Item</anno></c> is not an error; it results in as many, completely - independent, monitorings.</p> + unregistered, or unregistered and later registered on another + process.</p></note> + <p>The monitor is triggered either when the monitored process + terminates, is non existing, or if the connection to it is + lost. In the case the connection to it is lost, we do not know + if it still exist or not. After this type of monitor has been + triggered, the monitor is automatically removed.</p> + <p>When the monitor is triggered a <c>'DOWN'</c> message will + be sent to the monitoring process. A <c>'DOWN'</c> message has + the following pattern:</p> + <code type="none">{'DOWN', MonitorRef, Type, Object, Info}</code> + <p>where <c>MonitorRef</c> and <c>Type</c> are the same as + described above, and:</p> + <taglist> + <tag><c>Object</c></tag> + <item> + <p>equals:</p> + <taglist> + <tag><c><anno>Item</anno></c></tag> + <item>If <c><anno>Item</anno></c> was specified by a + pid.</item> + <tag><c>{RegisteredName, Node}</c></tag> + <item>If <c><anno>Item</anno></c> was specified as + <c>RegisteredName</c>, or <c>{RegisteredName, Node}</c> + where <c>Node</c> corresponds to the node that the + monitored process resides on.</item> + </taglist> + </item> + <tag><c>Info</c></tag> + <item> + <p>Either the exit reason of the process, <c>noproc</c> + (non-existing process), or <c>noconnection</c> (no + connection to the node where the monitored process + resides).</p></item> + </taglist> + <p>The monitoring is turned off either when the <c>'DOWN'</c> + message is sent, or when + <seealso marker="#demonitor/1">demonitor/1</seealso> + is called.</p> + <p>If an attempt is made to monitor a process on an older node + (where remote process monitoring is not implemented or one + where remote process monitoring by registered name is not + implemented), the call fails with <c>badarg</c>.</p> + <note> + <p>The format of the <c>'DOWN'</c> message changed in the 5.2 + version of the emulator (OTP release R9B) for monitor + <em>by registered name</em>. The <c>Object</c> element of + the <c>'DOWN'</c> message could in earlier versions + sometimes be the pid of the monitored process and sometimes + be the registered name. Now the <c>Object</c> element is + always a tuple consisting of the registered name and + the node name. Processes on new nodes (emulator version 5.2 + or greater) will always get <c>'DOWN'</c> messages on + the new format even if they are monitoring processes on old + nodes. Processes on old nodes will always get <c>'DOWN'</c> + messages on the old format.</p> + </note> + </item> + <tag><marker id="monitor_time_offset"/><c>time_offset</c></tag> + <item> + <p>Monitor changes in + <seealso marker="#time_offset/0">time offset</seealso> + between + <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang + monotonic time</seealso> and + <seealso marker="time_correction#Erlang_System_Time">Erlang + system time</seealso>. There is only one valid + <c><anno>Item</anno></c> in combination with the + <c>time_offset <anno>Type</anno></c>, namely the atom + <c>clock_service</c>. Note that the atom <c>clock_service</c> is + <em>not</em> the registered name of a process. In this specific + case it serves as an identifier of the runtime system internal + clock service at current runtime system instance.</p> + + <p>The monitor is triggered when the time offset is changed. + This either if the time offset value is changed, or if the + offset is changed from preliminary to final during + <seealso marker="#system_flag_time_offset">finalization + of the time offset</seealso> when the + <seealso marker="time_correction#Single_Time_Warp_Mode">single + time warp mode</seealso> is used. When a change from preliminary + to final time offset is made, the monitor will be triggered once + regardless of whether the time offset value was changed due to + the finalization or not.</p> + + <p>If the runtime system is in + <seealso marker="time_correction#Multi_Time_Warp_Mode">multi + time warp mode</seealso>, the time offset will be changed when + the runtime system detects that the + <seealso marker="time_correction#OS_System_Time">OS system + time</seealso> has changed. The runtime system will, however, + not detect this immediately when it happens. A task checking + the time offset is scheduled to execute at least once a minute, + so under normal operation this should be detected within a + minute, but during heavy load it might take longer time.</p> + + <p>The monitor will <em>not</em> be automatically removed + after it has been triggered. That is, repeated changes of + the time offset will trigger the monitor repeatedly.</p> + + <p>When the monitor is triggered a <c>'CHANGE'</c> message will + be sent to the monitoring process. A <c>'CHANGE'</c> message has + the following pattern:</p> + <code type="none">{'CHANGE', MonitorRef, Type, Item, NewTimeOffset}</code> + <p>where <c>MonitorRef</c>, <c><anno>Type</anno></c>, and + <c><anno>Item</anno></c> are the same as described above, and + <c>NewTimeOffset</c> is the new time offset.</p> + + <p>When the <c>'CHANGE'</c> message has been received you are + guaranteed not to retrieve the old time offset when calling + <seealso marker="#time_offset/0"><c>erlang:time_offset()</c></seealso>. + Note that you may observe the change of the time offset + when calling <c>erlang:time_offset()</c> before you + get the <c>'CHANGE'</c> message.</p> + + </item> + </taglist> + <p>Making several calls to <c>monitor/2</c> for the same + <c><anno>Item</anno></c> and/or <c><anno>Type</anno></c> is not + an error; it results in many, completely independent, + monitorings.</p> + <p>The monitor functionality is expected to be extended. That is, + other <c><anno>Type</anno></c>s and <c><anno>Item</anno></c>s + are expected to be supported in the future.</p> <note> - <p>The format of the <c>'DOWN'</c> message changed in the 5.2 - version of the emulator (OTP release R9B) for monitor <em>by registered name</em>. The <c>Object</c> element of - the <c>'DOWN'</c> message could in earlier versions - sometimes be the pid of the monitored process and sometimes - be the registered name. Now the <c>Object</c> element is - always a tuple consisting of the registered name and - the node name. Processes on new nodes (emulator version 5.2 - or greater) will always get <c>'DOWN'</c> messages on - the new format even if they are monitoring processes on old - nodes. Processes on old nodes will always get <c>'DOWN'</c> - messages on the old format.</p> + <p>If/when <c>monitor/2</c> is extended, other + possible values for <c>Tag</c>, <c>Object</c>, and + <c>Info</c> in the monitor message will be introduced.</p> </note> </desc> </func> @@ -2640,6 +2902,51 @@ os_prompt% </pre> </desc> </func> <func> + <name name="monotonic_time" arity="0"/> + <fsummary>Current Erlang monotonic time</fsummary> + <desc> + <p>Returns the current + <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang + monotonic time</seealso> in <c>native</c> + <seealso marker="#type_time_unit">time unit</seealso>. This + is a monotonically increasing time since some unspecified point in + time.</p> + + <note><p>This is a + <seealso marker="time_correction#Monotonically_Increasing">monotonically increasing</seealso> time, but <em>not</em> a + <seealso marker="time_correction#Strictly_Monotonically_Increasing">strictly monotonically increasing</seealso> + time. That is, consecutive calls to + <c>erlang:monotonic_time/0</c> may produce the same result.</p> + + <p>Different runtime system instances will use different + unspecified points in time as base for their Erlang monotonic clocks. + That is, it is <em>pointless</em> comparing monotonic times from + different runtime system instances. Different runtime system instances + may also place this unspecified point in time different relative + runtime system start. It may be placed in the future (time at start + will be a negative value), the past (time at start will be a + positive value), or the runtime system start (time at start will + be zero). The monotonic time as of runtime system start can be + retrieved by calling + <seealso marker="#system_info_start_time"><c>erlang:system_info(start_time)</c></seealso>.</p></note> + </desc> + </func> + <func> + <name name="monotonic_time" arity="1"/> + <fsummary>Current Erlang monotonic time</fsummary> + <desc> + <p>Returns the current + <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang + monotonic time</seealso> converted + into the <c><anno>Unit</anno></c> passed as argument.</p> + + <p>Same as calling + <seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#monotonic_time/0"><c>erlang:monotonic_time()</c></seealso><c>, + native, <anno>Unit</anno>)</c> + however optimized for commonly used <c><anno>Unit</anno></c>s.</p> + </desc> + </func> + <func> <name name="nif_error" arity="1"/> <fsummary>Stop execution with a given reason</fsummary> <desc> @@ -2734,6 +3041,13 @@ os_prompt% </pre> <type name="timestamp"/> <fsummary>Elapsed time since 00:00 GMT</fsummary> <desc> + <warning><p><em>This function is deprecated! Do not use it!</em> + See the users guide chapter + <seealso marker="time_correction">Time and Time Correction</seealso> + for more information. Specifically the + <seealso marker="time_correction#Dos_and_Donts">Dos and Dont's</seealso> + section for information on what to use instead of <c>erlang:now/0</c>. + </p></warning> <p>Returns the tuple <c>{MegaSecs, Secs, MicroSecs}</c> which is the elapsed time since 00:00 GMT, January 1, 1970 (zero hour) on the assumption that the underlying OS supports this. @@ -2746,10 +3060,6 @@ os_prompt% </pre> <p>It can only be used to check the local time of day if the time-zone info of the underlying operating system is properly configured.</p> - <p>If you do not need the return value to be unique and - monotonically increasing, use - <seealso marker="kernel:os#timestamp/0">os:timestamp/0</seealso> - instead to avoid some overhead.</p> </desc> </func> <func> @@ -4274,23 +4584,77 @@ os_prompt% </pre> </desc> </func> <func> - <name name="read_timer" arity="1"/> - <fsummary>Number of milliseconds remaining for a timer</fsummary> - <desc> - <p><c><anno>TimerRef</anno></c> is a timer reference returned by - <seealso marker="#send_after/3">erlang:send_after/3</seealso> - or - <seealso marker="#start_timer/3">erlang:start_timer/3</seealso>. - If the timer is active, the function returns the time in - milliseconds left until the timer will expire, otherwise - <c>false</c> (which means that <c><anno>TimerRef</anno></c> was never a - timer, that it has been cancelled, or that it has already - delivered its message).</p> + <name name="read_timer" arity="2"/> + <fsummary>Read the state of a timer</fsummary> + <desc> + <p> + Read the state of a timer that has been created by either + <seealso marker="#start_timer/4"><c>erlang:start_timer()</c></seealso>, + or <seealso marker="#send_after/4"><c>erlang:send_after()</c></seealso>. + <c><anno>TimerRef</anno></c> identifies the timer, and + was returned by the BIF that created the timer. + </p> + <p>Currently available <c><anno>Option</anno>s</c>:</p> + <taglist> + <tag><c>{async, Async}</c></tag> + <item> + <p> + Asynchronous request for state information. <c>Async</c> + defaults to <c>false</c> which will cause the operation + to be performed synchronously. In this case, the <c>Result</c> + will be returned by <c>erlang:read_timer()</c>. When + <c>Async</c> is set to <c>true</c>, <c>erlang:read_timer()</c> + will send an asynchronous request for the state information + to the timer service that manages the timer, and then return + <c>ok</c>. A message on the format <c>{read_timer, + <anno>TimerRef</anno>, <anno>Result</anno>}</c> will be + sent to the caller of <c>erlang:read_timer()</c> when the + operation has been processed. + </p> + </item> + </taglist> + <p> + More <c><anno>Option</anno></c>s may be added in the future. + </p> + <p> + When the <c><anno>Result</anno></c> equals <c>false</c>, a + timer corresponding to <c><anno>TimerRef</anno></c> could not + be found. This can be either because the timer had expired, + had been canceled, or because <c><anno>TimerRef</anno></c> + never has corresponded to a timer. If the timer has expired, + the timeout message has been sent, but it does not tell you + whether or not it has arrived at its destination yet. When the + <c><anno>Result</anno></c> is an integer, it represents the + time in milli-seconds left until the timer will expire. + </p> + <note> + <p> + The timer service that manages the timer may be co-located + with another scheduler than the scheduler that the calling + process is executing on. If this is the case, communication + with the timer service will take much longer time than if it + is located locally. If the calling process is in critical + path, and can do other things while waiting for the result + of this operation you want to use the <c>{async, true}</c> + option. If using the <c>{async, false}</c> option, the calling + process will be blocked until the operation has been + performed. + </p> + </note> <p>See also - <seealso marker="#send_after/3">erlang:send_after/3</seealso>, - <seealso marker="#start_timer/3">erlang:start_timer/3</seealso>, + <seealso marker="#send_after/4"><c>erlang:send_after/4</c></seealso>, + <seealso marker="#start_timer/4"><c>erlang:start_timer/4</c></seealso>, and - <seealso marker="#cancel_timer/1">erlang:cancel_timer/1</seealso>.</p> + <seealso marker="#cancel_timer/2"><c>erlang:cancel_timer/2</c></seealso>.</p> + </desc> + </func> + <func> + <name name="read_timer" arity="1"/> + <fsummary>Read the state of a timer</fsummary> + <desc> + <p>Read the state of a timer. The same as calling + <seealso marker="#read_timer/2"><c>erlang:read_timer(TimerRef, + [])</c></seealso>.</p> </desc> </func> <func> @@ -4439,31 +4803,26 @@ true</pre> </desc> </func> <func> + <name name="send_after" arity="4"/> + <fsummary>Start a timer</fsummary> + <desc> + <p> + Starts a timer. When the timer expires, the message + <c><anno>Msg</anno></c> will be sent to the process + identified by <c><anno>Dest</anno></c>. Appart from + the format of the message sent to + <c><anno>Dest</anno></c> when the timer expires + <c>erlang:send_after/4</c> works exactly as + <seealso marker="#start_timer/4"><c>erlang:start_timer/4</c></seealso>.</p> + </desc> + </func> + <func> <name name="send_after" arity="3"/> - <type_desc variable="Time">0 <= Time <= 4294967295</type_desc> <fsummary>Start a timer</fsummary> <desc> - <p>Starts a timer which will send the message <c>Msg</c> - to <c><anno>Dest</anno></c> after <c><anno>Time</anno></c> milliseconds.</p> - <p>If <c><anno>Dest</anno></c> is a <c>pid()</c> it has to be a <c>pid()</c> of a local process, dead or alive.</p> - <p>The <c><anno>Time</anno></c> value can, in the current implementation, not be greater than 4294967295.</p> - <p>If <c><anno>Dest</anno></c> is an <c>atom()</c>, it is supposed to be the name of - a registered process. The process referred to by the name is - looked up at the time of delivery. No error is given if - the name does not refer to a process.</p> - - <p>If <c><anno>Dest</anno></c> is a <c>pid()</c>, the timer will be automatically - canceled if the process referred to by the <c>pid()</c> is not alive, - or when the process exits. This feature was introduced in - erts version 5.4.11. Note that timers will not be - automatically canceled when <c><anno>Dest</anno></c> is an <c>atom</c>.</p> - <p>See also - <seealso marker="#start_timer/3">erlang:start_timer/3</seealso>, - <seealso marker="#cancel_timer/1">erlang:cancel_timer/1</seealso>, - and - <seealso marker="#read_timer/1">erlang:read_timer/1</seealso>.</p> - <p>Failure: <c>badarg</c> if the arguments does not satisfy - the requirements specified above.</p> + <p>Starts a timer. The same as calling + <seealso marker="#send_after/4"><c>erlang:send_after(<anno>Time</anno>, + <anno>Dest</anno>, <anno>Msg</anno>, [])</c></seealso>.</p> </desc> </func> <func> @@ -4869,34 +5228,81 @@ true</pre> </desc> </func> <func> - <name name="start_timer" arity="3"/> - <type_desc variable="Time">0 <= Time <= 4294967295</type_desc> + <name name="start_timer" arity="4"/> <fsummary>Start a timer</fsummary> <desc> - <p>Starts a timer which will send the message - <c>{timeout, <anno>TimerRef</anno>, <anno>Msg</anno>}</c> to <c><anno>Dest</anno></c> - after <c><anno>Time</anno></c> milliseconds.</p> - <p>If <c><anno>Dest</anno></c> is a <c>pid()</c> it has to be a <c>pid()</c> of a local process, dead or alive.</p> - <p>The <c><anno>Time</anno></c> value can, in the current implementation, not be greater than 4294967295.</p> - <p>If <c><anno>Dest</anno></c> is an <c>atom()</c>, it is supposed to be the name of - a registered process. The process referred to by the name is - looked up at the time of delivery. No error is given if - the name does not refer to a process.</p> - <p>If <c><anno>Dest</anno></c> is a <c>pid()</c>, the timer will be automatically - canceled if the process referred to by the <c>pid()</c> is not alive, - or when the process exits. This feature was introduced in - erts version 5.4.11. Note that timers will not be - automatically canceled when <c><anno>Dest</anno></c> is an <c>atom()</c>.</p> + <p> + Starts a timer. When the timer expires, the message + <c>{timeout, <anno>TimerRef</anno>, <anno>Msg</anno>}</c> + will be sent to the process identified by + <c><anno>Dest</anno></c>. + </p> + <p>Currently available <c><anno>Option</anno></c>s:</p> + <taglist> + <tag><c>{abs, Abs}</c></tag> + <item> + <p> + Absolute <c><anno>Time</anno></c> value. <c>Abs</c> + defaults to <c>false</c> which means that the + <c><anno>Time</anno></c> value will be interpreted + as a time in milli-seconds relative current + <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang + monotonic time</seealso>. When <c>Abs</c> is set to + <c>true</c>, the <c><anno>Time</anno></c> value will + be interpreted as an absolute Erlang monotonic time of + milli-seconds + <seealso marker="#type_time_unit">time unit</seealso>. + </p> + </item> + </taglist> + <p> + More <c><anno>Option</anno></c>s may be added in the future. + </p> + <p> + The absolute point in time that the timer is set to expire on + has to be in the interval + <c>[</c><seealso marker="#system_info_start_time"><c>erlang:system_info(start_time)</c></seealso><c>, + </c><seealso marker="#system_info_end_time"><c>erlang:system_info(end_time)</c></seealso><c>]</c>. + Further, if a relative time is specified, the <c><anno>Time</anno></c> value + is not allowed to be negative. + </p> + <p> + If <c><anno>Dest</anno></c> is a <c>pid()</c>, it has to + be a <c>pid()</c> of a process created on the current + runtime system instance. This process may or may not + have terminated. If <c><anno>Dest</anno></c> is an + <c>atom()</c>, it will be interpreted as the name of a + locally registered process. The process referred to by the + name is looked up at the time of timer expiration. No error + is given if the name does not refer to a process. + </p> + <p> + If <c><anno>Dest</anno></c> is a <c>pid()</c>, the timer will + be automatically canceled if the process referred to by the + <c>pid()</c> is not alive, or when the process exits. This + feature was introduced in erts version 5.4.11. Note that + timers will not be automatically canceled when + <c><anno>Dest</anno></c> is an <c>atom()</c>. + </p> <p>See also - <seealso marker="#send_after/3">erlang:send_after/3</seealso>, - <seealso marker="#cancel_timer/1">erlang:cancel_timer/1</seealso>, + <seealso marker="#send_after/4"><c>erlang:send_after/4</c></seealso>, + <seealso marker="#cancel_timer/2"><c>erlang:cancel_timer/2</c></seealso>, and - <seealso marker="#read_timer/1">erlang:read_timer/1</seealso>.</p> + <seealso marker="#read_timer/2"><c>erlang:read_timer/2</c></seealso>.</p> <p>Failure: <c>badarg</c> if the arguments does not satisfy the requirements specified above.</p> </desc> </func> <func> + <name name="start_timer" arity="3"/> + <fsummary>Start a timer</fsummary> + <desc> + <p>Starts a timer. The same as calling + <seealso marker="#start_timer/4"><c>erlang:start_timer(<anno>Time</anno>, + <anno>Dest</anno>, <anno>Msg</anno>, [])</c></seealso>.</p> + </desc> + </func> + <func> <name name="statistics" arity="1" clause_i="1"/> <fsummary>Information about context switches</fsummary> <desc> @@ -5496,6 +5902,35 @@ ok <p>Returns the old value of the flag.</p> </desc> </func> + <marker id="system_flag_time_offset"/> + <func> + <name name="system_flag" arity="2" clause_i="12"/> + <fsummary>Finalize the Time Offset</fsummary> + <desc> + <p>Finalizes the <seealso marker="#time_offset/0">time offset</seealso> + when the <seealso marker="time_correction#Single_Time_Warp_Mode">single + time warp mode</seealso> is being used. If another time warp mode than + the "single time warp mode" is used, the time offset state will be left + unchanged.</p> + <p>Returns the old state identifier. That is, if:</p> + <list> + <item><p><c>preliminary</c> is returned, finalization was + performed and the time offset is now final.</p></item> + + <item><p><c>final</c> is returned, the time offset was + already in the final state. This either due to another + <c>erlang:system_flag(time_offset, finalize)</c> call, or + due to the + <seealso marker="time_correction#No_Time_Warp_Mode">no + time warp mode</seealso> being used.</p></item> + + <item><p><c>volatile</c> is returned, the time offset + cannot be finalized due to the + <seealso marker="time_correction#Multi_Time_Warp_Mode">multi + time warp mode</seealso> being used.</p></item> + </list> + </desc> + </func> <func> <name name="system_info" arity="1" clause_i="1"/> <name name="system_info" arity="1" clause_i="2"/> @@ -5776,6 +6211,17 @@ ok <name name="system_info" arity="1" clause_i="53"/> <name name="system_info" arity="1" clause_i="54"/> <name name="system_info" arity="1" clause_i="55"/> + <name name="system_info" arity="1" clause_i="56"/> + <name name="system_info" arity="1" clause_i="57"/> + <name name="system_info" arity="1" clause_i="58"/> + <name name="system_info" arity="1" clause_i="59"/> + <name name="system_info" arity="1" clause_i="60"/> + <name name="system_info" arity="1" clause_i="61"/> + <name name="system_info" arity="1" clause_i="62"/> + <name name="system_info" arity="1" clause_i="63"/> + <name name="system_info" arity="1" clause_i="64"/> + <name name="system_info" arity="1" clause_i="65"/> + <name name="system_info" arity="1" clause_i="66"/> <fsummary>Information about the system</fsummary> <desc> <p>Returns various information about the current system @@ -5965,6 +6411,14 @@ ok (i.e. <c>system_info(dynamic_trace)</c> returns <c>dtrace</c> or <c>systemtap</c>).</p> </item> + <tag><marker id="system_info_end_time"/><c>end_time</c></tag> + <item><p>The last <seealso marker="#monotonic_time/0">Erlang monotonic + time</seealso> in <c>native</c> + <seealso marker="#type_time_unit">time unit</seealso> that + can be represented internally in the current Erlang runtime system + instance. The time between the + <seealso marker="#system_info_start_time">start time</seealso> and + the end time is at least a quarter of a millennium.</p></item> <tag><c>elib_malloc</c></tag> <item> <p>This option will be removed in a future release. @@ -6163,6 +6617,123 @@ ok documentation of versions in the system principles guide</seealso>.</p> </item> + <tag><marker id="system_info_os_monotonic_time_source"><c>os_monotonic_time_source</c></marker></tag> + <item> + <p>Returns a list containing information about the source of + <seealso marker="erts:time_correction#OS_Monotonic_Time">OS + monotonic time</seealso> that is used by the runtime system.</p> + <p>In case <c>[]</c> is returned, no OS monotonic time is + available. The list contains two-tuples with <c>Key</c>s + as first element, and <c>Value</c>s as second element. The + order if these tuples is undefined. Currently the following + tuples may be part of the list, but more tuples may be + introduced in the future:</p> + <taglist> + <tag><c>{function, Function}</c></tag> + <item><p><c>Function</c> is the name of the funcion + used. This tuple always exist if OS monotonic time is + available to the runtime system.</p></item> + + <tag><c>{clock_id, ClockId}</c></tag> + <item><p>This tuple only exist if <c>Function</c> + can be used with different clocks. <c>ClockId</c> + corresponds to the clock identifer used when calling + <c>Function</c>.</p></item> + + <tag><c>{resolution, OsMonotonicTimeResolution}</c></tag> + <item><p>Highest possible + <seealso marker="time_correction#Time_Resolution">resolution</seealso> + of current OS monotonic time source as parts per + second. If no resolution information can be retreived + from the OS, <c>OsMonotonicTimeResolution</c> will be + set to the resolution of the time unit of + <c>Function</c>s return value. That is, the actual + resolution may be lower than + <c>OsMonotonicTimeResolution</c>. Also note that + the resolution does not say anything about the + <seealso marker="time_correction#Time_Accuracy">accuracy</seealso>, + and that the + <seealso marker="time_correction#Time_Precision">precision</seealso> + might not align with the resolution. You do, + however, know that the precision won't be + better than + <c>OsMonotonicTimeResolution</c>.</p></item> + + <tag><c>{extended, Extended}</c></tag> + <item><p><c>Extended</c> equals <c>yes</c> if + the range of time values has been extended; + otherwise, <c>Extended</c> equals <c>no</c>. The + range needs to be extended if <c>Function</c> + returns values that wrap fast. This typically + is the case when the return value is a 32-bit + value.</p></item> + + <tag><c>{parallel, Parallel}</c></tag> + <item><p><c>Parallel</c> equals <c>yes</c> if + <c>Function</c> is called in parallel from multiple + threads. If it is not called in parallel, because + calls needs to be serialized, <c>Parallel</c> equals + <c>no</c>.</p></item> + + <tag><c>{time, OsMonotonicTime}</c></tag> + <item><p><c>OsMonotonicTime</c> equals current OS + monotonic time in <c>native</c> + <seealso marker="#type_time_unit">time unit</seealso>.</p></item> + </taglist> + </item> + <tag><marker id="system_info_os_system_time_source"><c>os_system_time_source</c></marker></tag> + <item> + <p>Returns a list containing information about the source of + <seealso marker="erts:time_correction#OS_System_Time">OS + system time</seealso> that is used by the runtime system.</p> + <p>The list contains two-tuples with <c>Key</c>s + as first element, and <c>Value</c>s as second element. The + order if these tuples is undefined. Currently the following + tuples may be part of the list, but more tuples may be + introduced in the future:</p> + <taglist> + <tag><c>{function, Function}</c></tag> + <item><p><c>Function</c> is the name of the funcion + used.</p></item> + + <tag><c>{clock_id, ClockId}</c></tag> + <item><p>This tuple only exist if <c>Function</c> + can be used with different clocks. <c>ClockId</c> + corresponds to the clock identifer used when calling + <c>Function</c>.</p></item> + + <tag><c>{resolution, OsSystemTimeResolution}</c></tag> + <item><p>Highest possible + <seealso marker="time_correction#Time_Resolution">resolution</seealso> + of current OS system time source as parts per + second. If no resolution information can be retreived + from the OS, <c>OsSystemTimeResolution</c> will be + set to the resolution of the time unit of + <c>Function</c>s return value. That is, the actual + resolution may be lower than + <c>OsSystemTimeResolution</c>. Also note that + the resolution does not say anything about the + <seealso marker="time_correction#Time_Accuracy">accuracy</seealso>, + and that the + <seealso marker="time_correction#Time_Precision">precision</seealso> + might not align with the resolution. You do, + however, know that the precision won't be + better than + <c>OsSystemTimeResolution</c>.</p></item> + + <tag><c>{parallel, Parallel}</c></tag> + <item><p><c>Parallel</c> equals <c>yes</c> if + <c>Function</c> is called in parallel from multiple + threads. If it is not called in parallel, because + calls needs to be serialized, <c>Parallel</c> equals + <c>no</c>.</p></item> + + <tag><c>{time, OsSystemTime}</c></tag> + <item><p><c>OsSystemTime</c> equals current OS + system time in <c>native</c> + <seealso marker="#type_time_unit">time unit</seealso>.</p></item> + </taglist> + </item> <tag><marker id="system_info_port_parallelism"><c>port_parallelism</c></marker></tag> <item><p>Returns the default port parallelism scheduling hint used. For more information see the @@ -6288,6 +6859,13 @@ ok <p>Returns <c>true</c> if the emulator has been compiled with smp support; otherwise, <c>false</c>.</p> </item> + <tag><marker id="system_info_start_time"/><c>start_time</c></tag> + <item><p>The <seealso marker="#monotonic_time/0">Erlang monotonic + time</seealso> in <c>native</c> + <seealso marker="#type_time_unit">time unit</seealso> at the + time when current Erlang runtime system instance started. See also + <seealso marker="#system_info_end_time"><c>erlang:system_info(end_time)</c></seealso>. + </p></item> <tag><c>system_version</c></tag> <item> <p>Returns a string containing version number and @@ -6311,12 +6889,64 @@ ok (<seealso marker="erts:erl_driver#driver_async">driver_async()</seealso>) as an integer.</p> </item> + <tag><marker id="system_info_time_correction"/><c>time_correction</c></tag> + <item><p>Returns a boolean value indicating whether + <seealso marker="time_correction#Time_Correction">time correction</seealso> + is enabled or not. + </p></item> + <tag><marker id="system_info_time_offset"/><c>time_offset</c></tag> + <item><p>Returns the state of the time offset:</p> + <taglist> + <tag><c>preliminary</c></tag> + <item><p>The time offset is preliminary, and will be changed + at a later time when being finalized. The preliminary time offset + is used during the preliminary phase of the + <seealso marker="time_correction#Single_Time_Warp_Mode">single + time warp mode</seealso>.</p></item> + + <tag><c>final</c></tag> + <item><p>The time offset is final. This + either due to the use of the + <seealso marker="time_correction#No_Time_Warp_Mode">no + time warp mode</seealso>, or due to the time offset having + been finalized when using the + <seealso marker="time_correction#Single_Time_Warp_Mode">single + time warp mode</seealso>.</p></item> + + <tag><c>volatile</c></tag> + <item><p>The time offset is volatile. That is, it may + change at any time. This due to the + <seealso marker="time_correction#Multi_Time_Warp_Mode">multi + time warp mode</seealso> being used.</p></item> + </taglist> + </item> + <tag><marker id="system_info_time_warp_mode"/><c>time_warp_mode</c></tag> + <item><p>Returns a value identifying the + <seealso marker="time_correction#Time_Warp_Modes">time warp + mode</seealso> being used:</p> + <taglist> + <tag><c>no_time_warp</c></tag> + <item><p>The <seealso marker="time_correction#No_Time_Warp_Mode">no + time warp mode</seealso> is being used.</p></item> + + <tag><c>single_time_warp</c></tag> + <item><p>The <seealso marker="time_correction#Single_Time_Warp_Mode">single + time warp mode</seealso> is being used.</p></item> + + <tag><c>multi_time_warp</c></tag> + <item><p>The <seealso marker="time_correction#Multi_Time_Warp_Mode">multi + time warp mode</seealso> is being used.</p></item> + </taglist> + </item> <tag><marker id="system_info_tolerant_timeofday"><c>tolerant_timeofday</c></marker></tag> <item> - <p>Returns whether compensation for sudden changes of system - time is <c>enabled</c> or <c>disabled</c>.</p> - <p>See also <seealso marker="erts:erl#+c">+c</seealso> - command line flag.</p> + <p>Returns whether a pre erts-7.0 backwards compatible compensation + for sudden changes of system time is <c>enabled</c> or <c>disabled</c>. + Such compensation is <c>enabled</c> when the + <seealso marker="#system_info_time_offset">time offset</seealso> is + <c>final</c>, and + <seealso marker="#system_info_time_correction">time correction</seealso> + is enabled.</p> </item> <tag><c>trace_control_word</c></tag> <item> @@ -6595,7 +7225,44 @@ ok </note> </desc> </func> + <func> + <name name="system_time" arity="0"/> + <fsummary>Current Erlang system time</fsummary> + <desc> + <p>Returns current + <seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso> + in <c>native</c> + <seealso marker="#type_time_unit">time unit</seealso>.</p> + + <p>Calling <c>erlang:system_time()</c> is equivalent to: + <seealso marker="#monotonic_time/0"><c>erlang:monotonic_time()</c></seealso><c> + + + </c><seealso marker="#time_offset/0"><c>erlang:time_offset()</c></seealso>.</p> + <note><p>This time is <em>not</em> a monotonically increasing time + in the general case. For more information, see the documentation of + <seealso marker="time_correction#Time_Warp_Modes">time warp modes</seealso> in the + ERTS User's Guide.</p></note> + </desc> + </func> + <func> + <name name="system_time" arity="1"/> + <fsummary>Current Erlang system time</fsummary> + <desc> + <p>Returns current + <seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso> + converted into the <c><anno>Unit</anno></c> passed as argument.</p> + + <p>Calling <c>erlang:system_time(<anno>Unit</anno>)</c> is equivalent to: + <seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#system_time/0"><c>erlang:system_time()</c></seealso><c>, + native, <anno>Unit</anno>)</c>.</p> + + <note><p>This time is <em>not</em> a monotonically increasing time + in the general case. For more information, see the documentation of + <seealso marker="time_correction#Time_Warp_Modes">time warp modes</seealso> in the + ERTS User's Guide.</p></note> + </desc> + </func> <func> <name name="term_to_binary" arity="1"/> <fsummary>Encode a term to an Erlang external term format binary</fsummary> @@ -6672,6 +7339,88 @@ ok </desc> </func> <func> + <name name="time_offset" arity="0"/> + <fsummary>Current time offset</fsummary> + <desc> + <p>Returns the current time offset between + <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang monotonic time</seealso> + and + <seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso> in + <c>native</c> <seealso marker="#type_time_unit">time unit</seealso>. + Current time offset added to an Erlang monotonic time gives + corresponding Erlang system time.</p> + + <p>The time offset may or may not change during operation depending + on the <seealso marker="time_correction#Time_Warp_Modes">time + warp mode</seealso> used.</p> + + <note> + <p>A change in time offset may be observed at slightly + different points in time by different processes.</p> + + <p>If the runtime system is in + <seealso marker="time_correction#Multi_Time_Warp_Mode">multi + time warp mode</seealso>, the time offset will be changed when + the runtime system detects that the + <seealso marker="time_correction#OS_System_Time">OS system + time</seealso> has changed. The runtime system will, however, + not detect this immediately when it happens. A task checking + the time offset is scheduled to execute at least once a minute, + so under normal operation this should be detected within a + minute, but during heavy load it might take longer time.</p> + </note> + </desc> + </func> + <func> + <name name="time_offset" arity="1"/> + <fsummary>Current time offset</fsummary> + <desc> + <p>Returns the current time offset between + <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang monotonic time</seealso> + and + <seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso> + converted into the <c><anno>Unit</anno></c> passed as argument.</p> + + <p>Same as calling + <seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#time_offset/0"><c>erlang:time_offset()</c></seealso><c>, native, <anno>Unit</anno>)</c> + however optimized for commonly used <c><anno>Unit</anno></c>s.</p> + </desc> + </func> + <func> + <name name="timestamp" arity="0"/> + <type name="timestamp"/> + <fsummary>Current Erlang System time</fsummary> + <desc> + <p>Returns current + <seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso> + on the format <c>{MegaSecs, Secs, MicroSecs}</c>. This format is + the same that <seealso marker="kernel:os#timestamp/0"><c>os:timestamp/0</c></seealso> + and the now deprecated <seealso marker="#now/0"><c>erlang:now/0</c></seealso> + uses. The reason for the existence of <c>erlang:timestamp()</c> is + purely to simplify usage for existing code that assumes this timestamp + format. Current Erlang system time can more efficiently be retrieved in + the time unit of your choice using + <seealso marker="#system_time/1"><c>erlang:system_time/1</c></seealso>.</p> + + <p>The <c>erlang:timestamp()</c> BIF is equivalent to:</p><code type="none"> +timestamp() -> + ErlangSystemTime = erlang:system_time(micro_seconds), + MegaSecs = ErlangSystemTime div 1000000000000, + Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000, + MicroSecs = ErlangSystemTime rem 1000000, + {MegaSecs, Secs, MicroSecs}.</code> + <p>It however use a native implementation which does + not build garbage on the heap and with slightly better + performance.</p> + + <note><p>This time is <em>not</em> a monotonically increasing time + in the general case. For more information, see the documentation of + <seealso marker="time_correction#Time_Warp_Modes">time warp modes</seealso> in the + ERTS User's Guide.</p></note> + </desc> + + </func> + <func> <name name="tl" arity="1"/> <fsummary>Tail of a list</fsummary> <desc> @@ -6815,7 +7564,9 @@ ok only allowed with <c>PidSpec==all</c>. If the host machine operating system does not support high resolution CPU time measurements, <c>trace/3</c> exits with - <c>badarg</c>.</p> + <c>badarg</c>. Note that most operating systems do + not synchronize this value across cores, so be prepared + that time might seem to go backwards when using this option.</p> </item> <tag><c>arity</c></tag> <item> @@ -7436,6 +8187,100 @@ ok </desc> </func> <func> + <name name="unique_integer" arity="0"/> + <fsummary>Get a unique integer value</fsummary> + <desc> + <p>Generates and returns an + <seealso marker="doc/efficiency_guide:advanced#unique_integers">integer + unique on current runtime system instance</seealso>. The same as calling + <seealso marker="#unique_integer/1"><c>erlang:unique_integer([])</c></seealso>.</p> + </desc> + </func> + <func> + <name name="unique_integer" arity="1"/> + <fsummary>Get a unique integer value</fsummary> + <desc> + <p>Generates and returns an + <seealso marker="doc/efficiency_guide:advanced#unique_integers">integer + unique on current runtime system + instance</seealso>. The integer is unique in the + sense that this BIF, using the same set of + modifiers, will not return the same integer more + than once on the current runtime system instance. + Each integer value can of course be constructed + by other means.</p> + + <p>By default, i.e. when <c>[]</c> is passed as + <c><anno>ModifierList</anno></c>, both negative and + positive integers will be returned. This is order + to be able to utilize the range of integers that do + not need to be heap allocated as much as possible. + By default the returned integers are also only + guaranteed to be unique, i.e., any integer returned + may be either smaller, or larger than previously + returned integers.</p> + + <p>Currently valid <c><anno>Modifier</anno></c>s:</p> + <taglist> + + <tag>positive</tag> + <item><p>Return only positive integers.</p> + <p>Note that by passing the <c>positive</c> modifier + you will get heap allocated integers (big-nums) + quicker.</p> + </item> + + <tag>monotonic</tag> + <item><p>Return + <seealso marker="time_correction#Strictly_Monotonically_Increasing">strictly + monotonically increasing</seealso> integers + corresponding to creation time. That is, the integer + returned will always be larger than previously + returned integers on the current runtime system + instance.</p> + <p>These values can be used when ordering events + on the runtime system instance. That is, if both + <c>X = erlang:unique_integer([monotonic])</c> and + <c>Y = erlang:unique_integer([monotonic])</c> are + executed by different processes (or the same + process) on the same runtime system instance and + <c>X < Y</c> we know that <c>X</c> was created + before <c>Y</c>.</p> + <warning><p>Strictly monotonically increasing values + are inherently quite expensive to generate and scales + poorly. This since the values needs to be + synchronized. That is, do not pass the <c>monotonic</c> + modifier unless you really need strictly monotonically + increasing values.</p></warning> + </item> + + </taglist> + + <p>All currently valid <c><anno>Modifier</anno></c>s + can be combined. Repeated (valid) + <c><anno>Modifier</anno></c>s in the <c>ModifierList</c> + are ignored.</p> + + <note><p>Note that the set of integers returned by + <c>unique_integer/1</c> using diffrent sets of + <c><anno>Modifier</anno></c>s <em>will overlap</em>. + For example, by calling <c>unique_integer([monotonic])</c>, + and <c>unique_integer([positive, monotonic])</c> + repeatedly, you will eventually see some integers being + returned by both calls.</p></note> + + <p>Failures:</p> + <taglist> + <tag><c>badarg</c></tag> + <item>if <c><anno>ModifierList</anno></c> is not a + proper list.</item> + <tag><c>badarg</c></tag> + <item>if <c><anno>Modifier</anno></c> is not a + valid modifier.</item> + </taglist> + </desc> + </func> + <func> <name name="unlink" arity="1"/> <fsummary>Remove a link, if there is one, to another process or port</fsummary> <desc> |