Example of waitpid in use

Question

I know that waitpid   is used to wait for a process to finish  but how would one use it exactly   Here what I want to do is  create two children and wait for the first child to finish  then kill the second child before exiting     Create two children pid t child1  pid t child2  child1   fork       wait for child1 to finish  then kill child2 waitpid       child1   kill child2

User · Accepted Answer

Syntax of waitpid     pid t waitpid pid t pid  int  status  int options     The value of pid can be     lt  -1  Wait for any child process whose process group ID is equal to the absolute value of pid  -1  Wait for any child process  0  Wait for any child process whose process group ID is equal to that of the calling process    0  Wait for the child whose process ID is equal to the value of pid    The value of options is an OR of zero or more of the following constants    WNOHANG  Return immediately if no child has exited  WUNTRACED  Also  return if a child has stopped  Status for traced children which have stopped is provided even if this option is not specified  WCONTINUED  Also return if a stopped child has been resumed by delivery of SIGCONT    For more help  use man waitpid

User · Answer

include  lt stdio h gt   include  lt sys types h gt   include  lt unistd h gt   include  lt stdlib h gt   include  lt sys wait h gt   int main         int pid      int status       printf  Parent   d n   getpid          pid   fork        if  pid    0           printf  Child  d n   getpid             sleep 2           exit EXIT SUCCESS            Comment from here to          Parent waits process pid  child      waitpid pid   amp status  0         Option is 0 since I check it later      if  WIFSIGNALED status            printf  Error n              else if  WEXITSTATUS status            printf  Exited Normally n            To Here and see the difference     printf  Parent   d n   getpid          return 0

User · Answer

The syntax is   pid t waitpid pid t pid  int  statusPtr  int options     1 where pid is the process of the child it should wait   2 statusPtr is a pointer to the location where status information for the terminating process is to be stored   3 specifies optional actions for the waitpid function  Either of the following option flags may be specified  or they can be combined with a bitwise inclusive OR operator   WNOHANG WUNTRACED WCONTINUED  If successful  waitpid returns the process ID of the terminated process whose status was reported  If unsuccessful  a -1 is returned   benifits over wait  1 Waitpid can used when you have more than one child for the process and you want to wait for particular child to get its execution done before parent resumes   2 waitpid supports job control  3 it supports non blocking of the parent process

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