Commit 5094db41 authored by Rémi Denis-Courmont's avatar Rémi Denis-Courmont

Work around QProcess bug (KDE bug #260719)

parent 9f8a21b2
......@@ -84,12 +84,11 @@ static void exit_timeout (int signum)
int main( int i_argc, const char *ppsz_argv[] )
/* The so-called POSIX-compliant MacOS X reportedly processes SIGPIPE even
* if it is blocked in all thread. Also some libraries want SIGPIPE blocked
* as they have no clue about signal masks.
* if it is blocked in all thread.
* Note: this is NOT an excuse for not protecting against SIGPIPE. If
* LibVLC runs outside of VLC, we cannot rely on this code snippet. */
signal (SIGPIPE, SIG_IGN);
/* Restore default for SIGCHLD in case parent ignores it. */
/* Restore SIGCHLD in case our parent process ignores it. */
signal (SIGCHLD, SIG_DFL);
......@@ -129,19 +128,17 @@ int main( int i_argc, const char *ppsz_argv[] )
sigset_t set;
sigemptyset (&set);
/* Synchronously intercepted POSIX signals.
/* VLC uses sigwait() to dequeue interesting signals.
* For this to work, those signals must be blocked in all threads,
* including the thread calling sigwait() (see the man page for details).
* In a threaded program such as VLC, the only sane way to handle signals
* is to block them in all threads but one - this is the only way to
* predict which thread will receive them. If any piece of code depends
* on delivery of one of this signal it is intrinsically not thread-safe
* and MUST NOT be used in VLC, whether we like it or not.
* There is only one exception: if the signal is raised with
* pthread_kill() - we do not use this in LibVLC but some pthread
* implementations use them internally. You should really use conditions
* for thread synchronization anyway.
* There are two advantages to sigwait() over traditional signal handlers:
* - delivery is synchronous: no need to worry about async-safety,
* - EINTR is not generated: other threads need not handle that error.
* That being said, some LibVLC programs do not use sigwait(). Therefore
* EINTR must still be handled cleanly, notably from poll() calls.
* Signal that request a clean shutdown, and force an unclean shutdown
* Signals that request a clean shutdown, and force an unclean shutdown
* if they are triggered again 2+ seconds later.
* We have to handle SIGTERM cleanly because of daemon mode. */
sigaddset (&set, SIGINT);
......@@ -149,14 +146,23 @@ int main( int i_argc, const char *ppsz_argv[] )
sigaddset (&set, SIGQUIT);
sigaddset (&set, SIGTERM);
/* Signals that cause a no-op:
* - SIGPIPE might happen with sockets and would crash VLC. It MUST be
* blocked by any LibVLC-dependent application, not just VLC.
* - SIGCHLD comes after exec*() (such as httpd CGI support) and must
* be dequeued to cleanup zombie processes.
/* SIGPIPE can happen and would crash the process. On modern systems,
* the MSG_NOSIGNAL flag protects socket write operations against SIGPIPE.
* But we still need to block SIGPIPE when:
* - writing to pipes,
* - using write() instead of send() for code not specific to sockets.
* LibVLC code assumes that SIGPIPE is blocked. Other LibVLC applications
* shall block it (or handle it somehow) too.
sigaddset (&set, SIGPIPE);
sigaddset (&set, SIGCHLD);
/* SIGCHLD must be dequeued to clean up zombie child processes.
* Furthermore the handler must not be set to SIG_IGN (see above). */
/* Unfortunately, the QProcess class from Qt4 has a bug. It installs a
* custom signal handlers and gets stuck if it is not called. So we cannot
* use sigwait() for SIGCHLD:
* */
//sigaddset (&set, SIGCHLD);
sigaddset (&set, SIGRTMIN);
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