When strace is used, waitpid() does not return immediately even if child processes has already changed state.

Issue

• When a process is traced by using strace, a call of waitpid() from the process does not return immediately even if a child process of the process has already changed its state.

• This behavior does not match the following description in waitpid(2):

  If a child has already changed state, then these calls return immediately.
  

• The problem only occurs if strace is used to monitor the child  processes, it does not occur if only the main process is monitored.