How to make parent wait for all child processes to finish

Question

I m hoping someone could shed some light on how to make the parent wait for ALL child processes to finish before continuing after the fork  I have cleanup code which I want to run but the child processes need to have returned before this can happen   for  int id 0  id lt n  id        if  fork    0           Child     exit 0             else          Parent

User · Answer

POSIX defines a function  wait NULL    It s the shorthand for waitpid -1  NULL  0    which will suspends the execution of the calling process until any one child process exits  Here  1st argument of waitpid indicates wait for any child process to end   In your case  have the parent call it from within your else branch

User · Answer

pid t child pid  wpid  int status   0     Father code  before child processes start   for  int id 0  id lt n  id          if   child pid   fork       0              child code         exit 0            while   wpid   wait  amp status    gt  0      this way  the father waits for all the child processes     Father code  After all child processes end    wait waits for a child process to terminate  and returns that child process s pid  On error  eg when there are no child processes   -1 is returned  So  basically  the code keeps waiting for child processes to finish  until the waiting errors out  and then you know they are all finished

User · Answer

Use waitpid   like this   pid t childPid      the child process that the execution will soon run inside of   childPid   fork     if childPid    0      fork succeeded             Do something       exit 0       else if childPid  lt  0      fork failed              log the error    else     Main  parent  process after fork succeeds            int returnStatus          waitpid childPid   amp returnStatus  0       Parent process waits here for child to terminate       if  returnStatus    0      Verify child process terminated without error                 printf  The child process terminated normally                    if  returnStatus    1                     printf  The child process terminated with an error

[c] How to make parent wait for all child processes to finish?

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