projects / OpenSPARC-T2-SAM / blame
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| 54 | <H2><A NAME="SECTION009110000000000000000"> | |
| 55 | 7.1.1 Example</A> | |
| 56 | </H2> | |
| 57 | <A NAME="Signal_Example"></A> | |
| 58 | <P> | |
| 59 | Here is a minimal example program. It uses the <tt class="function">alarm()</tt> | |
| 60 | function to limit the time spent waiting to open a file; this is | |
| 61 | useful if the file is for a serial device that may not be turned on, | |
| 62 | which would normally cause the <tt class="function">os.open()</tt> to hang | |
| 63 | indefinitely. The solution is to set a 5-second alarm before opening | |
| 64 | the file; if the operation takes too long, the alarm signal will be | |
| 65 | sent, and the handler raises an exception. | |
| 66 | ||
| 67 | <P> | |
| 68 | <div class="verbatim"><pre> | |
| 69 | import signal, os | |
| 70 | ||
| 71 | def handler(signum, frame): | |
| 72 | print 'Signal handler called with signal', signum | |
| 73 | raise IOError, "Couldn't open device!" | |
| 74 | ||
| 75 | # Set the signal handler and a 5-second alarm | |
| 76 | signal.signal(signal.SIGALRM, handler) | |
| 77 | signal.alarm(5) | |
| 78 | ||
| 79 | # This open() may hang indefinitely | |
| 80 | fd = os.open('/dev/ttyS0', os.O_RDWR) | |
| 81 | ||
| 82 | signal.alarm(0) # Disable the alarm | |
| 83 | </pre></div> | |
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