diff options
Diffstat (limited to 'manual/process.texi')
| -rw-r--r-- | manual/process.texi | 41 |
1 files changed, 26 insertions, 15 deletions
diff --git a/manual/process.texi b/manual/process.texi index 134d5c6143..28c9531f42 100644 --- a/manual/process.texi +++ b/manual/process.texi @@ -137,8 +137,8 @@ creating a process and making it run another program. @cindex parent process @cindex subprocess A new processes is created when one of the functions -@code{posix_spawn}, @code{fork}, or @code{vfork} is called. (The -@code{system} and @code{popen} also create new processes internally.) +@code{posix_spawn}, @code{fork}, @code{_Fork} or @code{vfork} is called. +(The @code{system} and @code{popen} also create new processes internally.) Due to the name of the @code{fork} function, the act of creating a new process is sometimes called @dfn{forking} a process. Each new process (the @dfn{child process} or @dfn{subprocess}) is allocated a process @@ -154,9 +154,10 @@ limited information about why the child terminated---for example, its exit status code. A newly forked child process continues to execute the same program as -its parent process, at the point where the @code{fork} call returns. -You can use the return value from @code{fork} to tell whether the program -is running in the parent process or the child. +its parent process, at the point where the @code{fork} or @code{_Fork} +call returns. You can use the return value from @code{fork} or +@code{_Fork} to tell whether the program is running in the parent process +or the child. @cindex process image Having several processes run the same program is only occasionally @@ -248,16 +249,13 @@ It is declared in the header file @file{unistd.h}. @deftypefun pid_t fork (void) @standards{POSIX.1, unistd.h} @safety{@prelim{}@mtsafe{}@asunsafe{@ascuplugin{}}@acunsafe{@aculock{}}} -@c The nptl/.../linux implementation safely collects fork_handlers into -@c an alloca()ed linked list and increments ref counters; it uses atomic -@c ops and retries, avoiding locking altogether. It then takes the -@c IO_list lock, resets the thread-local pid, and runs fork. The parent -@c restores the thread-local pid, releases the lock, and runs parent -@c handlers, decrementing the ref count and signaling futex wait if -@c requested by unregister_atfork. The child bumps the fork generation, -@c sets the thread-local pid, resets cpu clocks, initializes the robust -@c mutex list, the stream locks, the IO_list lock, the dynamic loader -@c lock, runs the child handlers, reseting ref counters to 1, and +@c The posix/fork.c implementation iterates over the fork_handlers +@c using a lock. It then takes the IO_list lock, resets the thread-local +@c pid, and runs fork. The parent releases the lock, and runs parent +@c handlers, and unlocks the internal lock. The child bumps the fork +@c generation, sets the thread-local pid, resets cpu clocks, initializes +@c the robust mutex list, the stream locks, the IO_list lock, the dynamic +@c loader lock, runs the child handlers, reseting ref counters to 1, and @c initializes the fork lock. These are all safe, unless atfork @c handlers themselves are unsafe. The @code{fork} function creates a new process. @@ -321,6 +319,19 @@ process is cleared. (The child process inherits its mask of blocked signals and signal actions from the parent process.) @end itemize +@deftypefun pid_t _Fork (void) +@standards{GNU, unistd.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +The @code{_Fork} function is similar to @code{fork}, but it does not invoke +any callbacks registered with @code{pthread_atfork}, nor does it reset +any internal state or locks (such as the @code{malloc} locks). In the +new subprocess, only async-signal-safe functions may be called, such as +@code{dup2} or @code{execve}. + +The @code{_Fork} function is an async-signal-safe replacement of @code{fork}. +It is a GNU extension. + +@end deftypefun @deftypefun pid_t vfork (void) @standards{BSD, unistd.h} |