rsync error: unexplained error

[David R. Staples]

I believe I have found the cause of the unexplained error (code ??) at main.c(line #).  In the version I’m running 2.5.2 (obtained from the Free Software Foundation) the line number is 576.  It appears the root cause is related to a race condition associated with the termination of child processes. If the signal handler for SIGCHILD is executed, as the result of a child termination, before the wait_process procedure is executed, the status of pid (as passed to wait_process) will not be available and the waitpid call in wait_process will fail with an ECHILD error.  If however, wait_process executes first, it will successfully obtain the exit status of pid and the sigchld_handler can execute, to eliminate zombies, with no adverse affects.  Since signal handlers execute asynchronously there is no way to predict when, if at all, a process will encounter this problem. I am providing below proposed new code that should resolve the problem.  Certainly I can make these changes within my own environment, but since I would like to remain consistent with the rsync project, I would like to here from someone regarding incorporation of these changes into rsync or an alternative (official) method to fixing this problem. I can be reached at [EMAIL PROTECTED]; [EMAIL PROTECTED]; or drstapl@empirenet.com Sincerely, David R. Staples Proposed new code in main.c #typedef struct       int pid;       int status; } pid_status;   pid_status pid_stat_table[10];   static RETSIGTYPE sigchld_handler(int val) { #ifdef WNOHANG       int      indx int      pid; int      status;       do {             pid = waitpid(-1, &status, WNOHANG);             for ( indx = 0; indx < 10; indx++ ) {                   if ( pid_stat_table[indx].pid == 0 ) {                         pid_stat_table[indx].pid = pid;                         pid_stat_table[indx].status = status;                         break;                   }             }       } while ( pid > 0 ); #endif }     void wait_process(pid_t pid, int *status) {       int waited_pid;       int indx;         do {             waited_pid = waitpid(pid, status, WNOHANG);             if ( waited_pid == 0) {             msleep(20);                   ioflush();             }       } while ( waited_pid == 0 );       if (( waited_pid == -1 ) && ( errno == ECHILD )) {             /* status of requested child no longer available.  Check */ /* to see if it was processed by the sigchld_handler.    */ for ( indx = 0; indx < 10; indx++ ) {       if ( pid == pid_stat_table[indx].pid ) {             *status = pid_stat_table[indx].status;             break;       } }       *status = WEXITSTATUS(*status); }