diff options
Diffstat (limited to 'erts/doc/src/erlang.xml')
| -rw-r--r-- | erts/doc/src/erlang.xml | 287 |
1 files changed, 176 insertions, 111 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index c3b0bc0d74..cb2cdec606 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>1996</year><year>2017</year> + <year>1996</year><year>2016</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -325,16 +325,11 @@ Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).</code> is <c>latin1</c>, one byte exists for each character in the text representation. If <c><anno>Encoding</anno></c> is <c>utf8</c> or - <c>unicode</c>, the characters are encoded using UTF-8 - (that is, characters from 128 through 255 are - encoded in two bytes).</p> + <c>unicode</c>, the characters are encoded using UTF-8 where + characters may require multiple bytes.</p> <note> - <p><c>atom_to_binary(<anno>Atom</anno>, latin1)</c> never - fails, as the text representation of an atom can only - contain characters from 0 through 255. In a future release, - the text representation - of atoms can be allowed to contain any Unicode character and - <c>atom_to_binary(<anno>Atom</anno>, latin1)</c> then fails if the + <p>As from Erlang/OTP 20, atoms can contain any Unicode character + and <c>atom_to_binary(<anno>Atom</anno>, latin1)</c> may fail if the text representation for <c><anno>Atom</anno></c> contains a Unicode character > 255.</p> </note> @@ -402,13 +397,11 @@ Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).</code> translation of bytes in the binary is done. If <c><anno>Encoding</anno></c> is <c>utf8</c> or <c>unicode</c>, the binary must contain - valid UTF-8 sequences. Only Unicode characters up - to 255 are allowed.</p> + valid UTF-8 sequences.</p> <note> - <p><c>binary_to_atom(<anno>Binary</anno>, utf8)</c> fails if - the binary contains Unicode characters > 255. - In a future release, such Unicode characters can be allowed and - <c>binary_to_atom(<anno>Binary</anno>, utf8)</c> does then not fail. + <p>As from Erlang/OTP 20, <c>binary_to_atom(<anno>Binary</anno>, utf8)</c> + is capable of encoding any Unicode character. Earlier versions would + fail if the binary contained Unicode characters > 255. For more information about Unicode support in atoms, see the <seealso marker="erl_ext_dist#utf8_atoms">note on UTF-8 encoded atoms</seealso> @@ -419,9 +412,7 @@ Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).</code> > <input>binary_to_atom(<<"Erlang">>, latin1).</input> 'Erlang' > <input>binary_to_atom(<<1024/utf8>>, utf8).</input> -** exception error: bad argument - in function binary_to_atom/2 - called as binary_to_atom(<<208,128>>,utf8)</pre> +'Ѐ'</pre> </desc> </func> @@ -733,6 +724,19 @@ hello </func> <func> + <name name="ceil" arity="1"/> + <fsummary>Returns the smallest integer not less than the argument</fsummary> + <desc> + <p>Returns the smallest integer not less than + <c><anno>Number</anno></c>. + For example:</p> + <pre> +> <input>ceil(5.5).</input> +6</pre> + <p>Allowed in guard tests.</p> + </desc> + </func> + <func> <name name="check_old_code" arity="1"/> <fsummary>Check if a module has old code.</fsummary> <desc> @@ -1480,6 +1484,20 @@ true</pre> </func> <func> + <name name="floor" arity="1"/> + <fsummary>Returns the largest integer not greater than the argument</fsummary> + <desc> + <p>Returns the largest integer not greater than + <c><anno>Number</anno></c>. + For example:</p> + <pre> +> <input>floor(-10.5).</input> +-11</pre> + <p>Allowed in guard tests.</p> + </desc> + </func> + + <func> <name name="fun_info" arity="1"/> <fsummary>Information about a fun.</fsummary> <desc> @@ -1667,6 +1685,12 @@ true</pre> the form <c>{garbage_collect, <anno>RequestId</anno>, <anno>GCResult</anno>}</c>. </item> + + <tag><c>{type, 'major' | 'minor'}</c></tag> + <item>Triggers garbage collection of requested type. Default value is + <c>'major'</c>, which would trigger a fullsweep GC. + The option <c>'minor'</c> is considered a hint and may lead to + either minor or major GC run.</item> </taglist> <p>If <c><anno>Pid</anno></c> equals <c>self()</c>, and no <c>async</c> option has been passed, the garbage @@ -1922,26 +1946,6 @@ os_prompt%</pre> </func> <func> - <name name="hash" arity="2"/> - <fsummary>Hash function (deprecated).</fsummary> - <desc> - <p>Returns a hash value for <c><anno>Term</anno></c> within the range - <c>1..<anno>Range</anno></c>. The maximum range is 1..2^27-1.</p> - <warning> - <p><em>This BIF is deprecated, as the hash value can differ on - different architectures.</em> The hash values for integer - terms > 2^27 and large binaries are - poor. The BIF is retained for backward compatibility - reasons (it can have been used to hash records into a file), - but all new code is to use one of the BIFs - <seealso marker="#phash/2"><c>erlang:phash/2</c></seealso> or - <seealso marker="#phash2/1"><c>erlang:phash2/1,2</c></seealso> - instead.</p> - </warning> - </desc> - </func> - - <func> <name name="hd" arity="1"/> <fsummary>Head of a list.</fsummary> <desc> @@ -2368,10 +2372,10 @@ os_prompt%</pre> <desc> <p>Returns the atom whose text representation is <c><anno>String</anno></c>.</p> - <p><c><anno>String</anno></c> can only contain ISO-latin-1 - characters (that is, numbers < 256) as the implementation does not - allow Unicode characters equal to or above 256 in atoms. - For more information on Unicode support in atoms, see + <p>As from Erlang/OTP 20, <c><anno>String</anno></c> may contain + any Unicode character. Earlier versions allowed only ISO-latin-1 + characters as the implementation did not allow Unicode characters + above 255. For more information on Unicode support in atoms, see <seealso marker="erl_ext_dist#utf8_atoms">note on UTF-8 encoded atoms</seealso> in section "External Term Format" in the User's Guide.</p> @@ -2544,13 +2548,6 @@ os_prompt%</pre> <name name="load_nif" arity="2"/> <fsummary>Load NIF library.</fsummary> <desc> - <note> - <p>Before Erlang/OTP R14B, NIFs were an - experimental feature. Versions before Erlang/OTP R14B can - have different and possibly incompatible NIF semantics and - interfaces. For example, in Erlang/OTP R13B03 the return value on - failure was <c>{error,Reason,Text}</c>.</p> - </note> <p>Loads and links a dynamic library containing native implemented functions (NIFs) for a module. <c><anno>Path</anno></c> is a file path to the shareable object/dynamic library file minus @@ -2580,14 +2577,22 @@ os_prompt%</pre> <item>The library did not fulfill the requirements as a NIF library of the calling module. </item> - <tag><c>load | reload | upgrade</c></tag> + <tag><c>load | upgrade</c></tag> <item>The corresponding library callback was unsuccessful. </item> + <tag><c>reload</c></tag> + <item>A NIF library is already loaded for this module instance. + The previously deprecated <c>reload</c> feature was removed in OTP 20. + </item> <tag><c>old_code</c></tag> <item>The call to <c>load_nif/2</c> was made from the old code of a module that has been upgraded; this is not allowed. </item> + <tag><c>notsup</c></tag> + <item>Lack of support. Such as loading NIF library for a + HiPE compiled module. + </item> </taglist> </desc> </func> @@ -3784,9 +3789,6 @@ RealSystem = system + MissedSystem</code> <c><anno>Term</anno></c> within the range <c>1..<anno>Range</anno></c>. The maximum value for <c><anno>Range</anno></c> is 2^32.</p> - <p>This BIF can be used instead of the old deprecated BIF - <c>erlang:hash/2</c>, as it calculates better hashes for - all data types, but consider using <c>phash2/1,2</c> instead.</p> </desc> </func> @@ -3821,10 +3823,6 @@ RealSystem = system + MissedSystem</code> <desc> <p>Returns a string corresponding to the text representation of <c><anno>Pid</anno></c>.</p> - <warning> - <p>This BIF is intended for debugging and is not to be used - in application programs.</p> - </warning> </desc> </func> @@ -4397,10 +4395,6 @@ RealSystem = system + MissedSystem</code> <desc> <p>Returns a string corresponding to the text representation of the port identifier <c><anno>Port</anno></c>.</p> - <warning> - <p>This BIF is intended for debugging. It is not to be used - in application programs.</p> - </warning> </desc> </func> @@ -4597,7 +4591,7 @@ RealSystem = system + MissedSystem</code> <p>If the process potentially can get many messages, you are advised to set the flag to <c>off_heap</c>. This because a garbage collection with many messages placed on - the heap can become extremly expensive and the process can + the heap can become extremely expensive and the process can consume large amounts of memory. Performance of the actual message passing is however generally better when not using flag <c>off_heap</c>.</p> @@ -6383,12 +6377,17 @@ lists:map( <c><anno>TotalTime</anno></c> is the total time duration since <seealso marker="#system_flag_scheduler_wall_time"> <c>scheduler_wall_time</c></seealso> - activation. The time unit is undefined and can be subject - to change between releases, OSs, and system restarts. - <c>scheduler_wall_time</c> is only to be used to - calculate relative values for scheduler-utilization. - <c><anno>ActiveTime</anno></c> can never exceed - <c><anno>TotalTime</anno></c>.</p> + activation for the specific scheduler. Note that + activation time can differ significantly between + schedulers. Currently dirty schedulers are activated + at system start while normal schedulers are activated + some time after the <c>scheduler_wall_time</c> + functionality is enabled. The time unit is undefined + and can be subject to change between releases, OSs, + and system restarts. <c>scheduler_wall_time</c> is only + to be used to calculate relative values for scheduler + utilization. <c><anno>ActiveTime</anno></c> can never + exceed <c><anno>TotalTime</anno></c>.</p> <p>The definition of a busy scheduler is when it is not idle and is not scheduling (selecting) a process or port, that is:</p> @@ -6406,15 +6405,37 @@ lists:map( <c>scheduler_wall_time</c></seealso> is turned off.</p> <p>The list of scheduler information is unsorted and can appear in different order between calls.</p> + <p>As of ERTS version 9.0, also dirty CPU schedulers will + be included in the result. That is, all scheduler threads + that are expected to handle CPU bound work. If you also + want information about dirty I/O schedulers, use + <seealso marker="#statistics_scheduler_wall_time_all"><c>statistics(scheduler_wall_time_all)</c></seealso> + instead.</p> + + <p>Normal schedulers will have scheduler identifiers in + the range <c>1 =< <anno>SchedulerId</anno> =< + </c><seealso marker="#system_info_schedulers"><c>erlang:system_info(schedulers)</c></seealso>. + Dirty CPU schedulers will have scheduler identifiers in + the range <c>erlang:system_info(schedulers) < + <anno>SchedulerId</anno> =< erlang:system_info(schedulers) + + + </c><seealso marker="#system_info_dirty_cpu_schedulers"><c>erlang:system_info(dirty_cpu_schedulers)</c></seealso>. + </p> + <note><p>The different types of schedulers handle + specific types of jobs. Every job is assigned to a specific + scheduler type. Jobs can migrate between different schedulers + of the same type, but never between schedulers of different + types. This fact has to be taken under consideration when + evaluating the result returned.</p></note> <p>Using <c>scheduler_wall_time</c> to calculate - scheduler-utilization:</p> + scheduler utilization:</p> <pre> > <input>erlang:system_flag(scheduler_wall_time, true).</input> false > <input>Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input> ok</pre> <p>Some time later the user takes another snapshot and calculates - scheduler-utilization per scheduler, for example:</p> + scheduler utilization per scheduler, for example:</p> <pre> > <input>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input> ok @@ -6429,11 +6450,32 @@ ok {7,0.973237033077876}, {8,0.9741297293248656}]</pre> <p>Using the same snapshots to calculate a total - scheduler-utilization:</p> + scheduler utilization:</p> <pre> > <input>{A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) -> - {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T.</input> + {Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), + TotalSchedulerUtilization = A/T.</input> +0.9769136803764825</pre> + <p>Total scheduler utilization will equal <c>1.0</c> when + all schedulers have been active all the time between the + two measurements.</p> + <p>Another (probably more) useful value is to calculate + total scheduler utilization weighted against maximum amount + of available CPU time:</p> + <pre> +> <input>WeightedSchedulerUtilization = (TotalSchedulerUtilization + * (erlang:system_info(schedulers) + + erlang:system_info(dirty_cpu_schedulers))) + / erlang:system_info(logical_processors_available).</input> 0.9769136803764825</pre> + <p>This weighted scheduler utilization will reach <c>1.0</c> + when schedulers are active the same amount of time as + maximum available CPU time. If more schedulers exist + than available logical processors, this value may + be greater than <c>1.0</c>.</p> + <p>As of ERTS version 9.0, the Erlang runtime system + with SMP support will as default have more schedulers + than logical processors. This due to the dirty schedulers.</p> <note> <p><c>scheduler_wall_time</c> is by default disabled. To enable it, use @@ -6444,6 +6486,31 @@ ok <func> <name name="statistics" arity="1" clause_i="12"/> + <fsummary>Information about each schedulers work time.</fsummary> + <desc> + <marker id="statistics_scheduler_wall_time_all"></marker> + <p>The same as + <seealso marker="#statistics_scheduler_wall_time"><c>statistics(scheduler_wall_time)</c></seealso>, + except that it also include information about all dirty I/O + schedulers.</p> + <p>Dirty IO schedulers will have scheduler identifiers in + the range + <seealso marker="#system_info_schedulers"><c>erlang:system_info(schedulers)</c></seealso><c> + + + </c><seealso marker="#system_info_dirty_cpu_schedulers"><c>erlang:system_info(dirty_cpu_schedulers)</c></seealso><c> < + <anno>SchedulerId</anno> =< erlang:system_info(schedulers) + + erlang:system_info(dirty_cpu_schedulers) + + + </c><seealso marker="#system_info_dirty_io_schedulers"><c>erlang:system_info(dirty_io_schedulers)</c></seealso>.</p> + <note><p>Note that work executing on dirty I/O schedulers + are expected to mainly wait for I/O. That is, when you + get high scheduler utilization on dirty I/O schedulers, + CPU utilization is <em>not</em> expected to be high due to + this work.</p></note> + </desc> + </func> + <func> + <name name="statistics" arity="1" clause_i="13"/> <fsummary>Information about active processes and ports.</fsummary> <desc><marker id="statistics_total_active_tasks"></marker> <p>Returns the total amount of active processes and ports in @@ -6463,7 +6530,7 @@ ok </func> <func> - <name name="statistics" arity="1" clause_i="13"/> + <name name="statistics" arity="1" clause_i="14"/> <fsummary>Information about the run-queue lengths.</fsummary> <desc><marker id="statistics_total_run_queue_lengths"></marker> <p>Returns the total length of the run queues. That is, the number @@ -6483,7 +6550,7 @@ ok </func> <func> - <name name="statistics" arity="1" clause_i="14"/> + <name name="statistics" arity="1" clause_i="15"/> <fsummary>Information about wall clock.</fsummary> <desc> <p>Returns information about wall clock. <c>wall_clock</c> can @@ -6689,11 +6756,6 @@ ok down to 3. Similarly, the number of dirty CPU schedulers online increases proportionally to increases in the number of schedulers online.</p> - <note> - <p>The dirty schedulers functionality is experimental. - Enable support for dirty schedulers when building OTP to - try out the functionality.</p> - </note> <p>For more information, see <seealso marker="#system_info_dirty_cpu_schedulers"> <c>erlang:system_info(dirty_cpu_schedulers)</c></seealso> and @@ -7196,8 +7258,8 @@ ok </func> <func> - <name name="system_info" arity="1" clause_i="10"/> - <name name="system_info" arity="1" clause_i="11"/> + <name name="system_info" arity="1" clause_i="12"/> + <name name="system_info" arity="1" clause_i="13"/> <fsummary>Information about the CPU topology of the system.</fsummary> <type name="cpu_topology"/> <type name="level_entry"/> @@ -7297,12 +7359,12 @@ ok </func> <func> - <name name="system_info" arity="1" clause_i="27"/> - <name name="system_info" arity="1" clause_i="28"/> - <name name="system_info" arity="1" clause_i="36"/> - <name name="system_info" arity="1" clause_i="37"/> + <name name="system_info" arity="1" clause_i="29"/> + <name name="system_info" arity="1" clause_i="30"/> <name name="system_info" arity="1" clause_i="38"/> <name name="system_info" arity="1" clause_i="39"/> + <name name="system_info" arity="1" clause_i="40"/> + <name name="system_info" arity="1" clause_i="41"/> <fsummary>Information about the default process heap settings.</fsummary> <type name="message_queue_data"/> <type name="max_heap_size"/> @@ -7345,12 +7407,6 @@ ok see <seealso marker="#process_flag_max_heap_size"> <c>process_flag(max_heap_size, MaxHeapSize)</c></seealso>.</p> </item> - <tag><c>min_heap_size</c></tag> - <item> - <p>Returns <c>{min_heap_size, <anno>MinHeapSize</anno>}</c>, - where <c><anno>MinHeapSize</anno></c> is the current - system-wide minimum heap size for spawned processes.</p> - </item> <tag><marker id="system_info_message_queue_data"/> <c>message_queue_data</c></tag> <item> @@ -7363,6 +7419,12 @@ ok <seealso marker="#process_flag_message_queue_data"> <c>process_flag(message_queue_data, MQD)</c></seealso>.</p> </item> + <tag><c>min_heap_size</c></tag> + <item> + <p>Returns <c>{min_heap_size, <anno>MinHeapSize</anno>}</c>, + where <c><anno>MinHeapSize</anno></c> is the current + system-wide minimum heap size for spawned processes.</p> + </item> <tag><c>min_bin_vheap_size</c></tag> <item> <p>Returns <c>{min_bin_vheap_size, @@ -7379,8 +7441,8 @@ ok <name name="system_info" arity="1" clause_i="7"/> <name name="system_info" arity="1" clause_i="8"/> <name name="system_info" arity="1" clause_i="9"/> - <name name="system_info" arity="1" clause_i="12"/> - <name name="system_info" arity="1" clause_i="13"/> + <name name="system_info" arity="1" clause_i="10"/> + <name name="system_info" arity="1" clause_i="11"/> <name name="system_info" arity="1" clause_i="14"/> <name name="system_info" arity="1" clause_i="15"/> <name name="system_info" arity="1" clause_i="16"/> @@ -7394,15 +7456,15 @@ ok <name name="system_info" arity="1" clause_i="24"/> <name name="system_info" arity="1" clause_i="25"/> <name name="system_info" arity="1" clause_i="26"/> - <name name="system_info" arity="1" clause_i="29"/> - <name name="system_info" arity="1" clause_i="30"/> + <name name="system_info" arity="1" clause_i="27"/> + <name name="system_info" arity="1" clause_i="28"/> <name name="system_info" arity="1" clause_i="31"/> <name name="system_info" arity="1" clause_i="32"/> <name name="system_info" arity="1" clause_i="33"/> <name name="system_info" arity="1" clause_i="34"/> <name name="system_info" arity="1" clause_i="35"/> - <name name="system_info" arity="1" clause_i="40"/> - <name name="system_info" arity="1" clause_i="41"/> + <name name="system_info" arity="1" clause_i="36"/> + <name name="system_info" arity="1" clause_i="37"/> <name name="system_info" arity="1" clause_i="42"/> <name name="system_info" arity="1" clause_i="43"/> <name name="system_info" arity="1" clause_i="44"/> @@ -7431,16 +7493,28 @@ ok <name name="system_info" arity="1" clause_i="67"/> <name name="system_info" arity="1" clause_i="68"/> <name name="system_info" arity="1" clause_i="69"/> + <name name="system_info" arity="1" clause_i="70"/> + <name name="system_info" arity="1" clause_i="71"/> <fsummary>Information about the system.</fsummary> <desc> <p>Returns various information about the current system (emulator) as specified by <c><anno>Item</anno></c>:</p> <taglist> - <tag><c>allocated_areas</c>, <c>allocator</c>, - <c>alloc_util_allocators</c>, <c>allocator_sizes</c></tag> + <tag><c>atom_count</c></tag> + <item> + <marker id="system_info_atom_count"></marker> + <p>Returns the number of atoms currently existing at the + local node. The value is given as an integer.</p> + </item> + <tag><c>atom_limit</c></tag> <item> - <p>See <seealso marker="#system_info_allocator_tags"> - above</seealso>.</p> + <marker id="system_info_atom_limit"></marker> + <p>Returns the maximum number of atoms allowed. + This limit can be increased at startup by passing + command-line flag + <seealso marker="erts:erl#+t"><c>+t</c></seealso> to + <c>erl(1)</c>. + </p> </item> <tag><c>build_type</c></tag> <item> @@ -7526,9 +7600,6 @@ ok <seealso marker="erts:erl#+SDcpu"><c>+SDcpu</c></seealso> or <seealso marker="erts:erl#+SDPcpu"><c>+SDPcpu</c></seealso> in <c>erl(1)</c>.</p> - <p>Notice that the dirty schedulers functionality is - experimental. Enable support for dirty schedulers when - building OTP to try out the functionality.</p> <p>See also <seealso marker="#system_flag_dirty_cpu_schedulers_online"> <c>erlang:system_flag(dirty_cpu_schedulers_online, @@ -7558,9 +7629,6 @@ ok startup by passing command-line flag <seealso marker="erts:erl#+SDcpu"><c>+SDcpu</c></seealso> in <c>erl(1)</c>.</p> - <p>Notice that the dirty schedulers functionality is - experimental. Enable support for dirty schedulers when - building OTP to try out the functionality.</p> <p>For more information, see <seealso marker="#system_info_dirty_cpu_schedulers"> <c>erlang:system_info(dirty_cpu_schedulers)</c></seealso>, @@ -7582,9 +7650,6 @@ ok <p>This value can be set at startup by passing command-line argument <seealso marker="erts:erl#+SDio"><c>+SDio</c></seealso> in <c>erl(1)</c>.</p> - <p>Notice that the dirty schedulers functionality is - experimental. Enable support for dirty schedulers when - building OTP to try out the functionality.</p> <p>For more information, see <seealso marker="#system_info_dirty_cpu_schedulers"> <c>erlang:system_info(dirty_cpu_schedulers)</c></seealso>, |