📄 fork.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>fork</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_005_167"> </a>NAME</h4><blockquote>fork - create a new process</blockquote><h4><a name = "tag_000_005_168"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="systypes.h.html">sys/types.h</a>>#include <<a href="unistd.h.html">unistd.h</a>>pid_t fork(void);</code></pre></blockquote><h4><a name = "tag_000_005_169"> </a>DESCRIPTION</h4><blockquote>The<i>fork()</i>function creates a new process. The new process (child process) is an exactcopy of the calling process (parent process) except as detailed below.<ul><p><li>The child process has a unique process ID.<p><li>The child process ID also does not match any active process group ID.<p><li>The child process has a different parent process ID(that is, the process ID of the parent process).<p><li>The child process has its own copy of the parent's file descriptors.Each of the child's file descriptors refers to the sameopen file description with the corresponding file descriptor of the parent.<p><li>The child process has its own copy of the parent's open directorystreams. Each open directory stream in the child process may sharedirectory stream positioning with the corresponding directorystream of the parent.<p><li>The child process may have its own copy of the parent's message cataloguedescriptors.<p><li>The child process' values of<i>tms_utime</i>,<i>tms_stime</i>,<i>tms_cutime</i>and<i>tms_cstime</i>are set to 0.<p><li>The time left until an alarm clock signal is reset to 0.<p><li>All<i>semadj</i>values are cleared.<p><li>File locks set by the parent process are not inherited by the child process.<p><li>The set of signals pending for the child process is initialised tothe empty set.<p><li>Interval timers are reset in the child process.<p><li>If the Semaphores option is supported,any semaphoresthat are open in the parent process will also be open in the childprocess.<p><li>If the Process Memory Locking option is supported,the child process does not inherit any address spacememory locks established by the parent process via calls to<i><a href="mlockall.html">mlockall()</a></i>or<i><a href="mlock.html">mlock()</a></i>.<p><li>Memory mappings created in the parent are retained in the child process.MAP_PRIVATE mappings inherited from the parent will also beMAP_PRIVATE mappings in the child,and any modifications to the data in these mappingsmade by the parent prior to calling<i>fork()</i>will be visible to the child.Any modifications to the data in MAP_PRIVATEmappings made by the parent after<i>fork()</i>returns will be visible only to the parent.Modifications to the data in MAP_PRIVATEmappings made by the child will be visible only to the child.<p><li>If the Process Scheduling option is supported,for the SCHED_FIFO and SCHED_RR scheduling policies,the child process inherits the policy and priority settingsof the parent process during a<i>fork()</i>function.For other scheduling policies, the policy and priority settings on<i>fork()</i>are implementation-dependent.<p><li>If the Timers option is supported,per-process timers created by the parent are not inheritedby the child process.<p><li>If the Message Passing option is supported,the child process has its own copyof the message queue descriptors of the parent.Each of the message descriptors of the child refersto the same open message queue descriptionas the corresponding message descriptor of the parent.<p><li>If the Asynchronous Input and Output option is supported,no asynchronous input or asynchronous output operations are inheritedby the child process.<p></ul><p>The inheritance of process characteristics not defined bythis document is implementation-dependent.After<i>fork()</i>,both the parent and the child processes are capable of executingindependently before either one terminates.<p>A process is created with a single thread.If a multi-threaded process calls<i>fork()</i>,the new process contains a replica of the calling threadand its entire address space,possibly including the states of mutexes and other resources.Consequently, to avoid errors, the child process may only executeasync-signal safe operations until such time as one of the<i>exec</i>functions is called.Fork handlers may be established by means of the<i><a href="pthread_atfork.html">pthread_atfork()</a></i>function in order to maintain application invariants across<i>fork()</i>calls.</blockquote><h4><a name = "tag_000_005_170"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>fork()</i>returns 0 to the child process and returns the process IDof the child process to the parent process.Otherwise, -1 is returned to the parent process, no child process iscreated, and<i>errno</i>is set to indicate the error.<br></blockquote><h4><a name = "tag_000_005_171"> </a>ERRORS</h4><blockquote>The<i>fork()</i>function will fail if:<dl compact><dt>[EAGAIN]<dd>The system lacked the necessary resources to create anotherprocess, or the system-imposed limiton the total number of processes underexecution system-wide or by a single user {CHILD_MAX} would be exceeded.</dl><p>The<i>fork()</i>function may fail if:<dl compact><dt>[ENOMEM]<dd>Insufficient storage space is available.</dl></blockquote><h4><a name = "tag_000_005_172"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_173"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_174"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_005_175"> </a>SEE ALSO</h4><blockquote><i><a href="alarm.html">alarm()</a></i>,<i><a href="exec.html">exec</a></i>,<i><a href="fcntl.html">fcntl()</a></i>,<i><a href="semop.html">semop()</a></i>,<i><a href="signal.html">signal()</a></i>,<i><a href="times.html">times()</a></i>,<i><a href="systypes.h.html"><sys/types.h></a></i>,<i><a href="unistd.h.html"><unistd.h></a></i>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 1 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -