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Unable to create a UDP client from thread?
Post 302481750 by Loic Domaigne on Sunday 19th of December 2010 05:14:28 PM
12-19-2010
Hi,
The answer from fpmurphy is short, but up to the point. Let me explain a little bit; In a multi-threaded process, a signal handler process-wide, that is global to all threads. However, when the signal is delivered, the system library / kernel picks up a particular thread that shall run the handler. This might be any thread in the process.
In your particular example, you wish that the handler runs in the context of thread1, so that the recvfrom() gets interrupted. But, unless you force it too, the handler may run in the context of the main thread. In that case, nothing will happen. This is likely what you are experiencing.
The way to force the handler to run in the context of thread1 (or equivalently, we say the signal to be delivered to thread1) is using pthread_sigmask() as mentioned by fpmurphy. Please refer to example in the link provided above, to see how it works. Incidentally, this example was my first contribution to the SUSv3 standard; so if you have questions please feel free to ask
And finally, I would suggest to resort other strategies than alarm() & co. to implement a timeout on the receive operation if you're multi-threaded.
Cheers, Loïc.
The answer from fpmurphy is short, but up to the point. Let me explain a little bit; In a multi-threaded process, a signal handler process-wide, that is global to all threads. However, when the signal is delivered, the system library / kernel picks up a particular thread that shall run the handler. This might be any thread in the process.
In your particular example, you wish that the handler runs in the context of thread1, so that the recvfrom() gets interrupted. But, unless you force it too, the handler may run in the context of the main thread. In that case, nothing will happen. This is likely what you are experiencing.
The way to force the handler to run in the context of thread1 (or equivalently, we say the signal to be delivered to thread1) is using pthread_sigmask() as mentioned by fpmurphy. Please refer to example in the link provided above, to see how it works. Incidentally, this example was my first contribution to the SUSv3 standard; so if you have questions please feel free to ask
And finally, I would suggest to resort other strategies than alarm() & co. to implement a timeout on the receive operation if you're multi-threaded.
Cheers, Loïc.
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LEARN ABOUT HPUX
pause
pause(2) System Calls Manual pause(2) NAME
pause - suspend process until signal SYNOPSIS
DESCRIPTION
suspends the calling process until it receives a signal. The signal must be one that is not currently set to be ignored or blocked (masked) by the calling process. If the signal causes termination of the calling process, does not return. If the signal is by the calling process and control is returned from the signal-catching function (see signal(5)), the calling process resumes execution from the point of suspension; with a return value of -1 from and set to APPLICATION USAGE
Threads Considerations Signal dispositions (such as catch/default/ignore) are shared by all threads in the process and blocked signal masks are maintained by each thread. Therefore, the signals being waited for should not be ignored by the process or blocked by the calling thread. will suspend only the calling thread until it receives a signal. If other threads in the process do not block the signal, the signal may be delivered to another thread in the process and the thread in may continue waiting. For this reason, the use of is recommended instead of for multi-threaded applications. For more information regarding signals and threads, refer to signal(5). SEE ALSO
alarm(2), kill(2), sigwait(2), wait(2), signal(5). STANDARDS CONFORMANCE
pause(2)