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Top Forums Programming Detecting if command is waiting for input Post 302222552 by slash_blog on Thursday 7th of August 2008 03:04:41 AM
Old 08-07-2008
Detecting if command is waiting for input

Hi,

After doing a fork and executing a shell, we execute (third party) commands which are essentially non-interactive. But some of them ask for input, under some (unforeseeable) circumstances. When this happens we go on waiting for output. Their is timeout, of course, but we don't seem to know if the process is actually doing some processing or is just simply waiting on us. Just wanted to ask if it is possible by some trickstery to find is the command is waiting for input. Note we can't parse the command output to check if it is waiting on input, because it varies across commands and becomes unmaintainable.

One possible approach that I can think of is looking out if the process is waiting on the stdin file descriptor. Could somebody elaborate as to how do I proceed in this direction.

thanks!
 

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pthread_cond_signal(3)					     Library Functions Manual					    pthread_cond_signal(3)

NAME
pthread_cond_signal - Wakes at least one thread that is waiting on the specified condition variable. LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so) SYNOPSIS
#include <pthread.h> int pthread_cond_signal( pthread_cond_t *cond); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: IEEE Std 1003.1c-1995, POSIX System Application Program Interface PARAMETERS
Condition variable to be signaled. DESCRIPTION
This routine unblocks at least one thread waiting on the specified condition variable cond. Calling this routine implies that data guarded by the associated mutex has changed, thus it might be possible for one of the waiting threads to proceed. In general, only one thread will be released. If no threads are waiting on the specified condition variable, this routine takes no action. The signal does not propagate to the next condition variable wait. This routine should be called when any thread waiting on the specified condition variable might find its predicate true, but only one thread should proceed. If more than one thread can proceed, or if any of the threads would not be able to proceed, then you must use pthread_cond_broadcast(3). The scheduling policy determines which thread is awakened. For policies SCHED_FIFO and SCHED_RR, a blocked thread is chosen in priority order, using first-in/first-out (FIFO) within priorities. If the calling thread holds the lock to the target condition variable's associated mutex while setting the variable's wait predicate, that thread can call pthread_cond_signal(3) to signal the variable even after releasing the lock on that mutex. However, for more predictable scheduling behavior, call pthread_cond_signal(3) before releasing the target condition variable's associated mutex. RETURN VALUES
If an error condition occurs, this routine returns an integer value indicating the type of error. Possible return values are as follows: Successful completion. The value specified by cond is not a valid condition variable. ERRORS
None RELATED INFORMATION
Functions: pthread_cond_broadcast(3), pthread_cond_destroy(3), pthread_cond_init(3), pthread_cond_timedwait(3), pthread_cond_wait(3) Manuals: Guide to DECthreads and Programmer's Guide delim off pthread_cond_signal(3)
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