sigaction.html

unix 下的C开发手册,还用详细的例程。

The signal was generated by the completion of an
asynchronous I/O request.

<dt>SI_MESGQ<dd>
The signal was generated by the arrival of a message on an
empty message queue.

</dl>
<p>
If the signal was not generated
by one of the functions or events listed above, the
<i>si_code</i>
will be set to an implementation-dependent value
that is not equal to any of the values defined above.
<p>
If the Realtime Signals Extension is supported,
and
<i>si_code</i>
is one of SI_QUEUE, SI_TIMER, SI_ASYNCIO, or SI_MESGQ, then
<i>si_value</i>
contains the application-specified signal value.
Otherwise, the contents of
<i>si_value</i>
are undefined.
<p>
<li>
The behaviour of a process is undefined after it returns normally
from a signal-catching function for a
&nbsp;SIGBUS,
SIGFPE, SIGILL or SIGSEGV signal that was not generated by
<i><a href="kill.html">kill()</a></i>,
<i><a href="sigqueue.html">sigqueue()</a></i>
or
<i><a href="raise.html">raise()</a></i>.
<p>
<li>
The system will not allow a process to catch the signals SIGKILL
and SIGSTOP.
<p>
<li>
If a process establishes a signal-catching function for the
SIGCHLD signal while it has a terminated child process for which
it has not waited, it is unspecified whether a SIGCHLD signal is
generated to indicate that child process.
<p>
<li>
When signal-catching functions are invoked asynchronously with process
execution, the behaviour of some of the functions defined by
this document is unspecified if they are called from a signal-catching
function.
<p>
The following table defines a set of interfaces that are either
reentrant or not interruptible by signals and are async-signal safe.
Therefore applications may invoke them, without
restriction, from signal-catching functions:
<p>
</ul>
<p>
</dl>
<h5><a name = "tag_000_008_581_003">&nbsp;</a>Base Interfaces</h5>
<p>
_exit()
access()
alarm()
cfgetispeed()
cfgetospeed()
cfsetispeed()
cfsetospeed()
chdir()
chmod()
chown()
close()
creat()
dup()
dup2()
execle()
execve()
fcntl()
fork()
fpathconf()
fstat()
fsync()
getegid()
geteuid()
getgid()
getgroups()
getpgrp()
getpid()
getppid()
getuid()
kill()
link()
lseek()
mkdir()
mkfifo()
open()
pathconf()
pause()
pipe()
raise()
read()
rename()
rmdir()
setgid()
setpgid()
setsid()
setuid()
sigaction()
sigaddset()
sigdelset()
sigemptyset()
sigfillset   ()
sigismember()
signal()
sigpending()
sigprocmask()
sigsuspend()
sleep()
stat()
sysconf()
tcdrain()
tcflow()
tcflush()
tcgetattr()
tcgetpgrp()
tcsendbreak()
tcsetattr()
tcsetpgrp()
time()
times()
umask()
uname()
unlink()
utime()
wait()
waitpid()
write()
<p>
<h5><a name = "tag_000_008_581_004">&nbsp;</a>Realtime Interfaces</h5>
<p><table <tr valign=top><td align=left><i><i>aio_error</i>()</i>
<td align=left><i><i>clock_gettime</i>()</i>
<td align=left><i><i>sigpause</i>()</i>
<td align=left><i><i>timer_getoverrun</i>()</i>
<tr valign=top><td align=left><i><i>aio_return</i>()</i>
<td align=left><i><i>fdatasync</i>()</i>
<td align=left><i><i>sigqueue</i>()</i>
<td align=left><i><i>timer_gettime</i>()</i>
<tr valign=top><td align=left><i><i>aio_suspend</i>()</i>
<td align=left><i><i>sem_post</i>()</i>
<td align=left><i><i>sigset</i>()</i>
<td align=left><i><i>timer_settime</i>()  </i>
</table>
<p>
All functions not in the above table are considered to be unsafe
with respect to signals.
In the presence of signals, all functions defined by this specification
will behave as defined when called from or interrupted by a signal-catching
function, with a single exception: when a signal interrupts an unsafe
function and
the signal-catching function calls an unsafe function, the behaviour
is undefined.
<p>
</>
<p>
</>
<p>
When a signal is delivered to a thread,
if the action of that signal specifies termination, stop, or continue,
the entire process will be terminated, stopped, or continued,
respectively.
<h5><a name = "tag_000_008_581_005">&nbsp;</a>Signal Effects on Other Functions</h5>
Signals affect the behaviour of certain functions defined by this
specification if delivered to a process while it is executing such a
function.
If the action of the signal is to terminate the process, the
process will be terminated and the function will not return.
If the action of the signal is to stop the process, the process
will stop until continued or terminated.
Generation of a SIGCONT signal for the process causes the process
to be continued, and the original function will continue at the point
the process was stopped.
If the action of the signal is to invoke a signal-catching
function, the signal-catching function will be invoked; in this
case the original function is said to be
<i>interrupted</i>
by the signal.
If the signal-catching function executes a
<b>return</b>
statement,
the behaviour of the interrupted function will be as described
individually for that function.
Signals that are ignored will not affect the behaviour of any
function; signals that are blocked will not affect the behaviour
of any function until they are unblocked and then delivered,
except as specified for the
<i><a href="sigpending.html">sigpending()</a></i>
and the 
<i><a href="sigwait.html">sigwait()</a></i>
functions.
<p>
The result of the use of
<i>sigaction()</i>
and a
<i><a href="sigwait.html">sigwait()</a></i>
function concurrently within a process on the same signal is
unspecified.
</blockquote><h4><a name = "tag_000_008_582">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion,
<i>sigaction()</i>
returns 0.  Otherwise -1 is returned,
<i>errno</i>
is set to indicate the error and no new signal-catching function
will be installed.
</blockquote><h4><a name = "tag_000_008_583">&nbsp;</a>ERRORS</h4><blockquote>
The
<i>sigaction()</i>
function will fail if:
<dl compact>

<dt>[EINVAL]<dd>
The
<i>sig</i>
argument is not a valid signal number or an attempt is made to
catch a signal that cannot be caught or ignore a signal that
cannot be ignored.

</dl>
<p>
The
<i>sigaction()</i>
function may fail if:
<dl compact>

<dt>[EINVAL]<dd>
An attempt was made to set the action to SIG_DFL for a signal
that cannot be caught or ignored (or both).

</dl>
</blockquote><h4><a name = "tag_000_008_584">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_008_585">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
The
<i>sigaction()</i>
function supersedes the
<i><a href="signal.html">signal()</a></i>
interface, and should be used in preference.  In particular,
<i>sigaction()</i>
and
<i><a href="signal.html">signal()</a></i>
should not be used in the same process to control the same signal.
The behaviour of reentrant interfaces, as defined in the
description,
is as specified by this specification, regardless of invocation from a
signal-catching function.
This is the only intended meaning of the statement that reentrant
interfaces may be used in signal-catching functions without
restrictions.
Applications must still consider all effects of such functions on
such things as data structures, files and process state.
In particular, application writers need to consider the
restrictions on interactions when interrupting
<i><a href="sleep.html">sleep()</a></i>
and interactions among multiple handles for a file description.
The fact that any specific interface is listed as reentrant does
not necessarily mean that invocation of that interface from a
signal-catching function is recommended.
<p>
In order to prevent errors arising from interrupting
non-reentrant function calls, applications should protect calls
to these functions either by blocking the appropriate signals or
through the use of some programmatic semaphore (see
<i><a href="semget.html">semget()</a></i>,
<i><a href="sem_init.html">sem_init()</a></i>,
<i><a href="sem_open.html">sem_open()</a></i>,
and so on).
Note in particular that even the &quot;safe&quot; functions may modify
<i>errno</i>;
the signal-catching function, if not executing as an independent
thread, may want to save and restore its value.
Naturally, the same principles apply to the reentrancy of
application routines and asynchronous data access.
Note that
<i><a href="longjmp.html">longjmp()</a></i>
and
<i><a href="siglongjmp.html">siglongjmp()</a></i>
are not in the list of reentrant interfaces.
This is because the code executing after
<i><a href="longjmp.html">longjmp()</a></i>
and
<i><a href="siglongjmp.html">siglongjmp()</a></i>
can call any unsafe functions with the same danger as calling those
unsafe functions directly from the signal handler.
Applications that use
<i><a href="longjmp.html">longjmp()</a></i>
and
<i><a href="siglongjmp.html">siglongjmp()</a></i>
from within signal handlers require rigorous protection in order to be
portable.
Many of the other functions that are excluded from the list are
traditionally implemented using either
<i><a href="malloc.html">malloc()</a></i>
or
<i><a href="free.html">free()</a></i>
functions or the standard I/O library, both of which
traditionally use data structures in a non-reentrant manner.
Because any combination of different functions using a common
data structure can cause reentrancy problems, this document does not
define the behaviour when any unsafe
function is called in a signal handler that interrupts an unsafe function.
<p>
If the signal occurs other than as the result of calling
<i><a href="abort.html">abort()</a></i>,
<i><a href="kill.html">kill()</a></i>
or
<i><a href="raise.html">raise()</a></i>,
the behaviour is undefined if the signal handler calls
any function in the standard library other than one of the
functions listed in the table above
or refers to any object with static storage duration
other than by assigning a value to a static storage duration
variable of type
<b>volatile</b>
<b>sig_atomic_t</b>.
Furthermore, if such a call fails,
the value of
<i>errno</i>
is indeterminate.
<p>
Usually, the signal is executed on the stack that was in effect before the
signal was delivered.  An alternate stack may be specified to receive a subset
of the signals being caught.
<p>
When the signal handler returns, the receiving process will resume execution
at the point it was interrupted unless the signal handler makes other
arrangements.  If
<i><a href="longjmp.html">longjmp()</a></i>
or
<i><a href="_longjmp.html">_longjmp()</a></i>
is used to leave the signal handler, then the signal mask must be explicitly
restored by the process.
<p>
The ISO&nbsp;POSIX-1 standard defines the third argument of a signal handling function when
SA_SIGINFO is set as a <b>void&nbsp;*</b> instead of a <b>ucontext_t&nbsp;*</b>,
but without requiring type checking.  New applications should explicitly cast
the third argument of the signal handling function to <b>ucontext_t *</b>.
<p>
The BSD optional four argument signal handling function is not supported by
this specification.  The BSD declaration would be:
<pre>
<code>
void handler(int <i>sig</i>, int <i>code</i>, struct sigcontext *<i>scp</i>,
    char *<i>addr</i>);
</code>
</pre>
<p>
where <i>sig</i> is the signal number, <i>code</i> is additional information on
certain signals, <i>scp</i> is a pointer to the sigcontext structure, and
<i>addr</i> is additional address information.  Much the same information is
available in the objects pointed to by the second argument of the
signal handler specified when SA_SIGINFO is set.
</blockquote><h4><a name = "tag_000_008_586">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
The
<i><a href="fpathconf.html">fpathconf()</a></i>
function is marked as an extension in the list of safe functions
because it is not included in the corresponding list in the ISO&nbsp;POSIX-1 standard,
but it is expected to be added in a future revision of that
standard.
</blockquote><h4><a name = "tag_000_008_587">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="bsd_signal.html">bsd_signal()</a></i>,
<i><a href="kill.html">kill()</a></i>,
<i><a href="_longjmp.html">_longjmp()</a></i>,
<i><a href="longjmp.html">longjmp()</a></i>,
<i><a href="raise.html">raise()</a></i>,
<i><a href="semget.html">semget()</a></i>,
<i><a href="sem_init.html">sem_init()</a></i>,
<i><a href="sem_open.html">sem_open()</a></i>,
<i><a href="sigaddset.html">sigaddset()</a></i>,
<i><a href="sigaltstack.html">sigaltstack()</a></i>,
<i><a href="sigdelset.html">sigdelset()</a></i>,
<i><a href="sigemptyset.html">sigemptyset()</a></i>,
<i><a href="sigfillset.html">sigfillset()</a></i>,
<i><a href="sigismember.html">sigismember()</a></i>,
<i><a href="signal.html">signal()</a></i>,
<i><a href="sigprocmask.html">sigprocmask()</a></i>,
<i><a href="sigsuspend.html">sigsuspend()</a></i>,
<i><a href="wait.html">wait()</a></i>,
<i><a href="wait3.html">wait3()</a></i>,
<i><a href="waitid.html">waitid()</a></i>,
<i><a href="waitpid.html">waitpid()</a></i>,
<i><a href="signal.h.html">&lt;signal.h&gt;</a></i>,
<i><a href="ucontext.h.html">&lt;ucontext.h&gt;</a></i>.
<br>
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from the POSIX.1-1988 standard.
</blockquote><hr size=2 noshade>
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