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copied!<p>Try to use a tool that traces system calls, e.g <code>strace</code> on Linux or <code>tusc</code> on HP-UX. When a deadlock occured, you should see the process hang in the blocking call. That's not a positive proof, though. It might be a regular block. You then need to determine whether the block may be resolved some time or not. This requires knowledge of the resource the process is waiting for.</p> <h3>Example</h3> <p>On RHEL4 there exists a... peculiarity... that may cause <code>ctime</code> to deadlock. Find an example program exhibiting this behaviour below:</p> <pre><code>#include <sys/time.h> #include <time.h> #include <signal.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> volatile char *r; void handler(int sig) { time_t t; time(&t); r = ctime(&t); } int main() { struct itimerval it; struct sigaction sa; time_t t; int counter = 0; memset(&sa, 0, sizeof(sa)); sa.sa_handler = handler; sigaction(SIGALRM, &sa, NULL); it.it_value.tv_sec = 0; it.it_value.tv_usec = 1000; it.it_interval.tv_sec = 0; it.it_interval.tv_usec = 1000; setitimer(ITIMER_REAL, &it, NULL); while(1) { counter++; time(&t); r = ctime(&t); printf("Loop %d\n",counter); } return 0; } </code></pre> <p>This will typically enter a deadlock after a couple thousand iterations. Now, attach <code>strace</code> like so</p> <pre><code>strace -s4096 -p<PID> </code></pre> <p>where <code>PID</code> is the program's process id. You'll see the program hang in a call with <code>FUTEX_WAIT</code> in the parameters. (I cannot quote the whole line as I currently don't have access to a RHEL4 machine, please excuse that).</p>

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