03-18-2010
Quote:
Originally Posted by
jrichemont
Hi Corona688. You are right. I already use WNOHANG with waitpid in a loop but only until that child has been dealt with. This is still liable to be interrupted though.
However you gave me an idea: I am using threads, I don't really need signals anyway and they mess with my head. What I did was start a thread and get it to sit in a loop with a blocking call to waitpid. As children die it gets unblocked, deals with it and loops back to blocking again. All in a nice serial manner.
I can simply ignore SIGCHLD now, that thread will pick up any children needing attention via waitpid.
Now, try as I might, I cannot break the system and I have it running in production today.
Cheers;
Jeremy
Good job, Jeremy!
You just discovered the way we usually deal with asynchronous signal in multi-threaded application. We spend a thread that waits (and consumes) synchronously the signal.
The function to wait synchronously for a signal is called sigwait(). You need in addition to ensure that the signal shall be delivered to the right thread, that is the one blocked in sigwait(). Pthreads offers such possibility with pthread_sigmask().
In your particular application, you luckier. First you can use waitpid(). And second, you can ignore SIGCHLD "signal redirection", since the default signal action for SIGCHLD is IGN.
Cheers,
Loïc.
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