diff options
Diffstat (limited to 'erts/doc/src/erlang.xml')
| -rw-r--r-- | erts/doc/src/erlang.xml | 136 |
1 files changed, 108 insertions, 28 deletions
diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index a603d5c2b8..8c438b0bd7 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -4,7 +4,7 @@ <erlref> <header> <copyright> - <year>1996</year><year>2011</year> + <year>1996</year><year>2012</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> @@ -215,9 +215,9 @@ representation of <c>Atom</c>. If <c>Encoding</c> is <c>latin1</c>, there will be one byte for each character in the text representation. If <c>Encoding</c> is <c>utf8</c> or - <c>unicode</c>, the characters will encoded using UTF-8 + <c>unicode</c>, the characters will be encoded using UTF-8 (meaning that characters from 16#80 up to 0xFF will be - encode in two bytes).</p> + encoded in two bytes).</p> <note><p>Currently, <c>atom_to_binary(Atom, latin1)</c> can never fail because the text representation of an atom can only contain @@ -268,7 +268,7 @@ <p>If <c>PosLen</c> in any way references outside the binary, a <c>badarg</c> exception is raised.</p> - <p><c>Start</c> is zero-based, i.e:</p> + <p><c>Start</c> is zero-based, i.e.:</p> <code> 1> Bin = <<1,2,3>> 2> binary_part(Bin,{0,2}). @@ -773,9 +773,9 @@ false</pre> turned off, nothing happens.</p> <p>Once <c>demonitor(MonitorRef)</c> has returned it is guaranteed that no <c>{'DOWN', MonitorRef, _, _, _}</c> message - due to the monitor will be placed in the callers message queue + due to the monitor will be placed in the caller's message queue in the future. A <c>{'DOWN', MonitorRef, _, _, _}</c> message - might have been placed in the callers message queue prior to + might have been placed in the caller's message queue prior to the call, though. Therefore, in most cases, it is advisable to remove such a <c>'DOWN'</c> message from the message queue after monitoring has been stopped. @@ -818,7 +818,7 @@ false</pre> <tag><c>flush</c></tag> <item> <p>Remove (one) <c>{_, MonitorRef, _, _, _}</c> message, - if there is one, from the callers message queue after + if there is one, from the caller's message queue after monitoring has been stopped.</p> <p>Calling <c>demonitor(MonitorRef, [flush])</c> is equivalent to the following, but more efficient:</p> @@ -847,7 +847,7 @@ false</pre> <item><p>The monitor was not found and could not be removed. This probably because someone already has placed a <c>'DOWN'</c> message corresponding to this monitor - in the callers message queue. + in the caller's message queue. </p> </item> </taglist> @@ -3909,7 +3909,7 @@ os_prompt%</pre> <item> <p>Return the current call stack back-trace (<em>stacktrace</em>) of the process. The stack has the same format as returned by - <seealso marker="#get_stacktrace/1">erlang:get_stacktrace/0</seealso>. + <seealso marker="#get_stacktrace/0">erlang:get_stacktrace/0</seealso>. </p> </item> <tag><c>{dictionary, Dictionary}</c></tag> @@ -4881,6 +4881,7 @@ true</pre> <v>Type, Res -- see below</v> </type> <desc> + <p>All times are in milliseconds unless otherwise specified.</p> <p>Returns information about the system as specified by <c>Type</c>:</p> <taglist> @@ -4894,15 +4895,20 @@ true</pre> <item> <p>Returns <c>{Total_Exact_Reductions, Exact_Reductions_Since_Last_Call}</c>.</p> - <p><em>NOTE:</em><c>statistics(exact_reductions)</c> is - a more expensive operation than - <seealso marker="#statistics_reductions">statistics(reductions)</seealso> - especially on an Erlang machine with SMP support.</p> + <note><p><c>statistics(exact_reductions)</c> is + a more expensive operation than + <seealso marker="#statistics_reductions">statistics(reductions)</seealso> + especially on an Erlang machine with SMP support.</p> + </note> </item> <tag><c>garbage_collection</c></tag> <item> <p>Returns <c>{Number_of_GCs, Words_Reclaimed, 0}</c>. This information may not be valid for all implementations.</p> + <pre> +> <input>statistics(garbage_collection).</input> +{85,23961,0} +</pre> </item> <tag><c>io</c></tag> <item> @@ -4914,12 +4920,18 @@ true</pre> <tag><marker id="statistics_reductions"><c>reductions</c></marker></tag> <item> <p>Returns - <c>{Total_Reductions, Reductions_Since_Last_Call}</c>.</p> - <p><em>NOTE:</em> From erts version 5.5 (OTP release R11B) - this value does not include reductions performed in current - time slices of currently scheduled processes. If an - exact value is wanted, use - <seealso marker="#statistics_exact_reductions">statistics(exact_reductions)</seealso>.</p> + <c>{Total_Reductions, Reductions_Since_Last_Call}</c>.</p> + <note> + <p>From erts version 5.5 (OTP release R11B) + this value does not include reductions performed in current + time slices of currently scheduled processes. If an + exact value is wanted, use + <seealso marker="#statistics_exact_reductions">statistics(exact_reductions)</seealso>.</p> + </note> + <pre> +> <input>statistics(reductions).</input> +{2046,11} +</pre> </item> <tag><c>run_queue</c></tag> <item> @@ -4932,7 +4944,74 @@ true</pre> Note that the run-time is the sum of the run-time for all threads in the Erlang run-time system and may therefore be greater than the wall-clock time.</p> + <pre> +> <input>statistics(runtime).</input> +{1690,1620} +</pre> + </item> + <tag><marker id="statistics_scheduler_wall_time"><c>scheduler_wall_time</c></marker></tag> + <item> + <p>Returns a list of tuples with + <c>{SchedulerId, ActiveTime, TotalTime}</c>, where <c>SchedulerId</c> is an integer id of the scheduler, <c>ActiveTime</c> is + the duration the scheduler has been busy, <c>TotalTime</c> is the total time duration since + <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso> + activation. The time unit is not defined and may be subject to change + between releases, operating systems and system restarts. + <c>scheduler_wall_time</c> should only be used to calculate relative + values for scheduler-utilization. <c>ActiveTime</c> can never exceed <c>TotalTime</c>. + </p> + + <p>The definition of a busy scheduler is when it is not idle or not + scheduling (selecting) a process or port, meaning; executing process + code, executing linked-in-driver or NIF code, executing + built-in-functions or any other runtime handling, garbage collecting + or handling any other memory management. Note, a scheduler may also be + busy even if the operating system has scheduled out the scheduler + thread. + </p> + + <p> + Returns <c>undefined</c> if the system flag <seealso marker="#system_flag_scheduler_wall_time"> + scheduler_wall_time</seealso> is turned off. + </p> + + <p>The list of scheduler information is unsorted and may appear in different order + between calls. + </p> + <p>Using <c>scheduler_wall_time</c> to calculate 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 we will take another snapshot and calculate scheduler-utilization per scheduler.</p> +<pre> +> <input>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input> +ok +> <input>lists:map(fun({{I, A0, T0}, {I, A1, T1}}) -> + {I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).</input> +[{1,0.9743474730177548}, + {2,0.9744843782751444}, + {3,0.9995902361669045}, + {4,0.9738012596572161}, + {5,0.9717956667018103}, + {6,0.9739235846420741}, + {7,0.973237033077876}, + {8,0.9741297293248656}] +</pre> + <p>Using the same snapshots to calculate a total 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> +0.9769136803764825 +</pre> + + <note> + <p><c>scheduler_wall_time</c> is by default disabled. Use <c>erlang:system_flag(scheduler_wall_time, true)</c> to enable it. </p> + </note> </item> + <tag><c>wall_clock</c></tag> <item> <p>Returns @@ -4942,14 +5021,6 @@ true</pre> opposed to runtime or CPU time.</p> </item> </taglist> - <p>All times are in milliseconds.</p> - <pre> -> <input>statistics(runtime).</input> -{1690,1620} -> <input>statistics(reductions).</input> -{2046,11} -> <input>statistics(garbage_collection).</input> -{85,23961,0}</pre> </desc> </func> <func> @@ -5305,6 +5376,14 @@ true</pre> flags. </p> </item> + <tag><marker id="system_flag_scheduler_wall_time"><c>erlang:system_flag(scheduler_wall_time, Boolean)</c></marker></tag> + <item> + <p>Turns on/off scheduler wall time measurements. </p> + <p>For more information see, + <seealso marker="#statistics_scheduler_wall_time">erlang:statistics(scheduler_wall_time)</seealso>. + </p> + </item> + <tag><marker id="system_flag_schedulers_online"><c>erlang:system_flag(schedulers_online, SchedulersOnline)</c></marker></tag> <item> <p>Sets the amount of schedulers online. Valid range is @@ -5316,6 +5395,7 @@ true</pre> <seealso marker="#system_info_schedulers_online">erlang:system_info(schedulers_online)</seealso>. </p> </item> + <tag><c>erlang:system_flag(trace_control_word, TCW)</c></tag> <item> <p>Sets the value of the node's trace control word to @@ -7090,7 +7170,7 @@ true</pre> <c>Id</c> has no effect on the caller in the future (unless the link is setup again). If caller is trapping exits, an <c>{'EXIT', Id, _}</c> message due to the link might have - been placed in the callers message queue prior to the call, + been placed in the caller's message queue prior to the call, though. Note, the <c>{'EXIT', Id, _}</c> message can be the result of the link, but can also be the result of <c>Id</c> calling <c>exit/2</c>. Therefore, it <em>may</em> be |