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copied!<p>First of all - the use of signals should be avoided at all cost:</p> <p>1) It may lead to a deadlock. SIGALRM may reach the process BEFORE the blocking syscall (imagine super-high load in the system!) and the syscall will not be interrupted. Deadlock.</p> <p>2) Playing with signals may have some nasty non-local consequences. For example, syscalls in other threads may be interrupted which usually is not what you want. Normally syscalls are restarted when (not a deadly) signal is received. When you set up a signal handler it automatically turns off this behavior for the whole process, or thread group so to say. Check 'man siginterrupt' on that.</p> <p>Believe me - I met two problems before and they are not fun at all.</p> <p>In some cases the blocking can be avoided explicitely - I strongly recommend using select() and friends (check select module in Python) to handle blocking writes and reads. This will not solve blocking open() call, though.</p> <p>For that I've tested this solution and it works well for named pipes. It opens in a non-blocking way, then turns it off and uses select() call to eventually timeout if nothing is available.</p> <pre><code>import sys, os, select, fcntl f = os.open(sys.argv[1], os.O_RDONLY | os.O_NONBLOCK) flags = fcntl.fcntl(f, fcntl.F_GETFL, 0) fcntl.fcntl(f, fcntl.F_SETFL, flags & ~os.O_NONBLOCK) r, w, e = select.select([f], [], [], 2.0) if r == [f]: print 'ready' print os.read(f, 100) else: print 'unready' os.close(f) </code></pre> <p>Test this with:</p> <pre><code>mkfifo /tmp/fifo python <code_above.py> /tmp/fifo (1st terminal) echo abcd > /tmp/fifo (2nd terminal) </code></pre> <p>With some additional effort select() call can be used as a main loop of the whole program, aggregating all events - you can use libev or libevent, or some Python wrappers around them.</p> <p>When you can't explicitely force non-blocking behavior, say you just use an external library, then it's going to be much harder. Threads may do, but obviously it is not a state-of-the-art solution, usually being just wrong.</p> <p>I'm afraid that in general you can't solve this in a robust way - it really depends on WHAT you block.</p>

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