On Sat, Oct 31, 2009 at 4:55 PM, Kris Kennaway <k...@freebsd.org> wrote:
> Peter Steele wrote: > >> I have an application running a number of threads. I've had recent >> instances where the code below is causing a core dump to occur: >> >> char fstatCmd; >> char *fstatOut = "/tmp/fstat.out"; >> sprintf(fstatCmd, "fstat | grep -v USER | wc -l >%s", fstatOut); >> rc = system(fstatCmd); >> >> The call is simply intended to get a count of the current open handles. >> The system call though causes a core: >> >> #0 0x0000000801058307 in _spinunlock () from /lib/libthr.so.3 >> #1 0x00000008011d0afb in _malloc_postfork () from /lib/libc.so.7 >> #2 0x000000080105c5fb in fork () from /lib/libthr.so.3 >> #3 0x0000000801191aae in system () from /lib/libc.so.7 >> #4 0x00000008010553aa in system () from /lib/libthr.so.3 >> #5 0x000000000040b6f9 in mythread at myapp.c:461 >> #6 0x0000000801056a88 in pthread_getprio () from /lib/libthr.so.3 >> >> There appears to be some kind of thread-safe issue going on. I have a >> number of threads that are monitoring various items, waking up a differing >> intervals to do their respective tasks. Do I need to put in a global mutex >> so that the threads never attempt to make simultaneous system() calls? >> Curiously, only this particular system() call appears to be causing a core. >> > > In UNIX it is not safe to perform arbitrary actions after forking a > multi-threaded process. You're basically expected to call exec soon after > the fork, although you can do certain other work if you are very careful. > > The reason for this is that after the fork, only one thread will be running > in the child, and if that thread tries to acquire a lock or other > formerly-shared resource it may deadlock or crash, because the child process > is no longer accessing the same memory location as the threads in the parent > process (it gets a separate copy of the address space at the time of fork, > which may not be in a consistent state from the point of view of the thread > library). > Are you saying system/popen can't be used in threads? Is there a workaround? ( forking manual and executing exec? ) Would calling 'system("exec fstat | ... > result.txt")' make any difference? just curious, kind regards, usleep _______________________________________________ firstname.lastname@example.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "freebsd-questions-unsubscr...@freebsd.org"