rsync error: unexplained error

David R. Staples drstapl at
Sun Sep 1 15:17:01 EST 2002

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 drstaples at; drstaples at; or drstapl at
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;




      } while ( pid > 0 );





void wait_process(pid_t pid, int *status)


      int waited_pid;

      int indx;


      do {

            waited_pid = waitpid(pid, status, WNOHANG);

            if ( waited_pid == 0) {




      } 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;




      *status = WEXITSTATUS(*status);



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