Description of problem:
We are using the command
  ps -e | grep $PID >/dev/null
to determine if the process $PID is still alive.

We found that sometimes this command exits with a nonzero
status (which means $PID is not found in the output of
ps -e) even though the process $PID is alive.

How reproducible:
Sometimes

Steps to Reproduce:
1. Start a process.
2. The primordial thread of the process writes the pid to a file.
3. Read the file to get the pid.
4. Execute the command
     ps -e | grep $PID >/dev/null || echo "process not detectable"
5. Execute the command
     kill $PID
   to terminate the process (even if it is not alive).
5. The process has a signal handler for SIGTERM that writes
   "SIGTERM received\n" to fd 1.

Sometimes, we see both the "process not detectable" and
"SIGTERM received" messages, indicating that ps -e fails
to list a process that is still alive.

Additional info:

This problem occurs very rarely on Linux.  It never occurs
on other Unix platforms (Solaris, HP-UX, AIX, and OSF1).

The process we are monitoring is a multithreaded process
that creates 8 threads.  I don't know if this piece of
information is relevant.

We are now using the command
  kill -0 $PID >/dev/null 2>/dev/null || echo "process not detectable"
to detect whether the process $PID is still alive.  This
method has been reliable on Linux and other Unix platforms.