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Diffstat (limited to 'system/doc/reference_manual/processes.xml')
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1 files changed, 63 insertions, 48 deletions
diff --git a/system/doc/reference_manual/processes.xml b/system/doc/reference_manual/processes.xml index 95ae0672ec..f656d0318e 100644 --- a/system/doc/reference_manual/processes.xml +++ b/system/doc/reference_manual/processes.xml @@ -4,20 +4,21 @@ <chapter> <header> <copyright> - <year>2003</year><year>2013</year> + <year>2003</year><year>2015</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. + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. </legalnotice> @@ -32,8 +33,8 @@ <section> <title>Processes</title> <p>Erlang is designed for massive concurrency. Erlang processes are - light-weight (grow and shrink dynamically) with small memory - footprint, fast to create and terminate and the scheduling + lightweight (grow and shrink dynamically) with small memory + footprint, fast to create and terminate, and the scheduling overhead is low.</p> </section> @@ -46,10 +47,10 @@ spawn(Module, Name, Args) -> pid() Args = [Arg1,...,ArgN] ArgI = term()</pre> <p><c>spawn</c> creates a new process and returns the pid.</p> - <p>The new process will start executing in - <c>Module:Name(Arg1,...,ArgN)</c> where the arguments is + <p>The new process starts executing in + <c>Module:Name(Arg1,...,ArgN)</c> where the arguments are the elements of the (possible empty) <c>Args</c> argument list.</p> - <p>There exist a number of other <c>spawn</c> BIFs, for example + <p>There exist a number of other <c>spawn</c> BIFs, for example, <c>spawn/4</c> for spawning a process at another node.</p> </section> @@ -60,18 +61,25 @@ spawn(Module, Name, Args) -> pid() atom and is automatically unregistered if the process terminates:</p> <table> <row> + <cell align="left" valign="middle"><em>BIF</em></cell> + <cell align="left" valign="middle"><em>Description</em></cell> + </row> + <row> <cell align="left" valign="middle"><c>register(Name, Pid)</c></cell> <cell align="left" valign="middle">Associates the name <c>Name</c>, an atom, with the process <c>Pid</c>.</cell> </row> <row> <cell align="left" valign="middle"><c>registered()</c></cell> - <cell align="left" valign="middle">Returns a list of names which have been registered using<c>register/2</c>.</cell> + <cell align="left" valign="middle">Returns a list of names that + have been registered using <c>register/2</c>.</cell> </row> <row> <cell align="left" valign="middle"><c>whereis(Name)</c></cell> - <cell align="left" valign="middle">Returns the pid registered under <c>Name</c>, or<c>undefined</c>if the name is not registered.</cell> + <cell align="left" valign="middle">Returns the pid registered + under <c>Name</c>, or <c>undefined </c>if the name is not + registered.</cell> </row> - <tcaption>Name Registration BIFs.</tcaption> + <tcaption>Name Registration BIFs</tcaption> </table> </section> @@ -79,22 +87,25 @@ spawn(Module, Name, Args) -> pid() <marker id="term"></marker> <title>Process Termination</title> <p>When a process terminates, it always terminates with an - <em>exit reason</em>. The reason may be any term.</p> + <em>exit reason</em>. The reason can be any term.</p> <p>A process is said to terminate <em>normally</em>, if the exit reason is the atom <c>normal</c>. A process with no more code to execute terminates normally.</p> - <p>A process terminates with exit reason <c>{Reason,Stack}</c> + <p>A process terminates with an exit reason <c>{Reason,Stack}</c> when a run-time error occurs. See - <seealso marker="errors#exit_reasons">Error and Error Handling</seealso>.</p> - <p>A process can terminate itself by calling one of the BIFs - <c>exit(Reason)</c>, - <c>erlang:error(Reason)</c>, <c>erlang:error(Reason, Args)</c>, - <c>erlang:fault(Reason)</c> or <c>erlang:fault(Reason, Args)</c>. - The process then terminates with reason <c>Reason</c> for - <c>exit/1</c> or <c>{Reason,Stack} for the others</c>.</p> - <p>A process may also be terminated if it receives an exit signal + <seealso marker="errors#exit_reasons">Exit Reasons</seealso>.</p> + <p>A process can terminate itself by calling one of the + following BIFs:</p> + <list type="bulleted"> + <item><c>exit(Reason)</c></item> + <item><c>erlang:error(Reason)</c></item> + <item><c>erlang:error(Reason, Args)</c></item> + </list> + <p>The process then terminates with reason <c>Reason</c> for + <c>exit/1</c> or <c>{Reason,Stack}</c> for the others.</p> + <p>A process can also be terminated if it receives an exit signal with another exit reason than <c>normal</c>, see - <seealso marker="#errors">Error Handling</seealso> below.</p> + <seealso marker="#errors">Error Handling</seealso>.</p> </section> <section> @@ -113,35 +124,39 @@ spawn(Module, Name, Args) -> pid() <title>Links</title> <p>Two processes can be <em>linked</em> to each other. A link between two processes <c>Pid1</c> and <c>Pid2</c> is created - by <c>Pid1</c> calling the BIF <c>link(Pid2)</c> (or vice versa). + by <c>Pid1</c> calling the BIF <c>link(Pid2)</c> (or conversely). There also exist a number of <c>spawn_link</c> BIFs, which spawn and link to a process in one operation.</p> <p>Links are bidirectional and there can only be one link between two processes. Repeated calls to <c>link(Pid)</c> have no effect.</p> <p>A link can be removed by calling the BIF <c>unlink(Pid)</c>.</p> <p>Links are used to monitor the behaviour of other processes, see - <seealso marker="#errors">Error Handling</seealso> below.</p> + <seealso marker="#errors">Error Handling</seealso>.</p> </section> <section> <marker id="errors"></marker> <title>Error Handling</title> <p>Erlang has a built-in feature for error handling between - processes. Terminating processes will emit exit signals to all - linked processes, which may terminate as well or handle the exit + processes. Terminating processes emit exit signals to all + linked processes, which can terminate as well or handle the exit in some way. This feature can be used to build hierarchical program structures where some processes are supervising other - processes, for example restarting them if they terminate + processes, for example, restarting them if they terminate abnormally.</p> - <p>Refer to OTP Design Principles for more information about - OTP supervision trees, which uses this feature.</p> + <p>See <seealso marker= + "doc/design_principles:des_princ#otp design principles"> + OTP Design Principles</seealso> for more information about + OTP supervision trees, which use this feature.</p> <section> <title>Emitting Exit Signals</title> - <p>When a process terminates, it will terminate with an <em>exit reason</em> as explained in <seealso marker="#term">Process Termination</seealso> above. This exit reason is emitted in + <p>When a process terminates, it terminates with an + <em>exit reason</em> as explained in <seealso marker="#term"> + Process Termination</seealso>. This exit reason is emitted in an <em>exit signal</em> to all linked processes.</p> <p>A process can also call the function <c>exit(Pid,Reason)</c>. - This will result in an exit signal with exit reason + This results in an exit signal with exit reason <c>Reason</c> being emitted to <c>Pid</c>, but does not affect the calling process.</p> </section> @@ -156,14 +171,14 @@ spawn(Module, Name, Args) -> pid() <p>A process can be set to trap exit signals by calling:</p> <pre> process_flag(trap_exit, true)</pre> - <p>When a process is trapping exits, it will not terminate when + <p>When a process is trapping exits, it does not terminate when an exit signal is received. Instead, the signal is transformed - into a message <c>{'EXIT',FromPid,Reason}</c> which is put into - the mailbox of the process just like a regular message.</p> + into a message <c>{'EXIT',FromPid,Reason}</c>, which is put into + the mailbox of the process, just like a regular message.</p> <p>An exception to the above is if the exit reason is <c>kill</c>, - that is if <c>exit(Pid,kill)</c> has been called. This will - unconditionally terminate the process, regardless of if it is - trapping exit signals or not.</p> + that is if <c>exit(Pid,kill)</c> has been called. This + unconditionally terminates the process, regardless of if it is + trapping exit signals.</p> </section> </section> @@ -180,12 +195,12 @@ process_flag(trap_exit, true)</pre> <p>If <c>Pid2</c> does not exist, the 'DOWN' message is sent immediately with <c>Reason</c> set to <c>noproc</c>.</p> <p>Monitors are unidirectional. Repeated calls to - <c>erlang:monitor(process, Pid)</c> will create several, - independent monitors and each one will send a 'DOWN' message when + <c>erlang:monitor(process, Pid)</c> creates several + independent monitors, and each one sends a 'DOWN' message when <c>Pid</c> terminates.</p> <p>A monitor can be removed by calling <c>erlang:demonitor(Ref)</c>.</p> - <p>It is possible to create monitors for processes with registered + <p>Monitors can be created for processes with registered names, also at other nodes.</p> </section> |