Re: [Chicken-hackers] Fixing the "process" procedure to be safe against execve() errors

[Lassi Kortela]

The the way things are done in the current version of Chicken is wonky 
because the outline is like this:

      child = fork();
      if (!child) {
          // This code runs in the child process.
          execve(exefile, argv, envp);
          // Not only is the errno value not returned to the parent,
          // but there is no call to exit() at all. So the child
          // keeps running the user's Scheme program after a failed
          // execve() until the program error-exits. Since the parent
          // also continues running the Scheme program, there are now
          // two copies of it running concurrently.
      }

So if you wrap a Scheme exception handler around the (process ...) call 
to catch and handle execve() errors (e.g. to write an error message or 
return false from the enclosing procedure), that exception handler is 
run in the child process (which is supposed to have no other job except 
to call execve() or die trying). And if you handle the exception instead 
of letting it propagate all the way up the Scheme stack, then the child 
Scheme process will eventually exit with success code zero (since your 
Scheme program succeeded) and the parent process will think exefile 
succeeded.

TL;DR multiprocessing is complicated :)