[Caml-list] Re: Race conditions with asynchronous exceptions in standard library

[oleg@okmij.org]

Just a few clarifications. The posted Queue code gives the
segmentation fault when compiled with ocamlopt without threads. When
bytecode-compiled, the code is accidentally safe, at least on my
platform. The bytecode interpreter checks for signals when executing
any of the `application' instructions or popping the exception
handler. It just so happens that no function application instructions
were executed in the critical section of the standard library Queue
code. That is a mere accident however: a new version of the standard
library (or Batteries) might add some sort of debugging printing; or
the code generation will change to emit calls to auxiliary, debugging
or tracing facilities.

Incidentally, comments in the bytecode interpreter justify a particular
piece of code by saying that a signal handler may raise an
exception. Thus Xavier Leroy certainly did allow for such signal
handlers, at least as a possibility.

Mark Shinwell wrote:
> Specifically in the case of signal handlers, I would recommend
> restricting processing in them to an absolute minimum, and in
> particular not throwing exceptions.

If this is the consensus, to which INRIA assents, it ought to be
written in the user documentation, alongside of other warnings (like
living in harmony with GC). At the same time, one should describe the
recommended solution to Yit's original problem, to interrupt a
long-running library function with a timeout.