0000108: Bug/Feature in Unix.open_process_full

Notes
(0000385) administrator (administrator) 2000-05-16 11:18	> I have a problem with the Unix.open_process_full function. > It crashes with a nasty exception: > uncaught exception Failure("equal: abstract value") > on my test program. > > I've written a program that recreates the error, it is attached. Thanks, I had no problems reproducing the crash. It turns out to be an absurdity in the implementation of Unix.open_process* and Unix.close_process. Namely, to keep track of which processes are attached to which channels, the Unix module uses an hash table indexed by I/O channels. This is totally bogus since (in OCaml 2.04 and 3.00 at least), equality on channels is unreliable and raises Failure("equal: abstract value") unless the two channel objects are physically equal. Any program that has several processes created with Unix.open_process active at the same time may cause the Failure exception. Fortunately, OCaml 3.00 makes it very easy to attach a meaningful equality function to I/O channels. This is what the patch below does, and with it your test program works fine. > This kind of functionality (closing the channel prior to performing > Unix.close_process_full) is required in many programs. For example, > PGP uses this kind of call sequence. OK. This doesn't seem to cause any problems, since it is legal to close an I/O channel several times. Thanks for the bug report. Best regards, - Xavier Leroy Index: csl/byterun/io.c diff -u csl/byterun/io.c:1.41 csl/byterun/io.c:1.42 --- csl/byterun/io.c:1.41 Mon Apr 17 22:01:34 2000 +++ csl/byterun/io.c Tue May 16 11:11:51 2000 @@ -10,7 +10,7 @@ /* / /*********************************************************************/ -/ $Id: io.c,v 1.41 2000/04/17 20:01:34 doligez Exp $ / +/ $Id: io.c,v 1.42 2000/05/16 09:11:51 xleroy Exp $ / / Buffered input/output. / @@ -376,10 +376,17 @@ stat_free(chan); } +static int compare_channel(value vchan1, value vchan2) +{ + struct channel chan1 = Channel(vchan1); + struct channel * chan2 = Channel(vchan2); + return (chan1 == chan2) ? 0 : (chan1 < chan2) ? -1 : 1; +} + static struct custom_operations channel_operations = { "_chan", finalize_channel, - custom_compare_default, + compare_channel, custom_hash_default, custom_serialize_default, custom_deserialize_default

(0000386) administrator (administrator) 2000-05-16 11:19	Fixed on 2000-05-16 by Xavier (added proper comparison function to I/O channels).

Issue History
Date Modified	Username	Field	Change
2005-11-18 10:13	administrator	New Issue

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