Calling system() in multi-threads.

Thu Jul 17 15:44:46 GMT 2025

On 2025年7月17日 17:19:49 +0200
Corinna Vinschen wrote:
> On Jul 17 23:14, Takashi Yano via Cygwin wrote:
> > Hi Corinna,
> > 
> > On 2025年7月16日 17:36:42 +0200
> > Corinna Vinschen wrote:
> > > On Jul 16 23:52, Takashi Yano via Cygwin wrote:
> > > > Do you have any idea?
> > > 
> > > Locking would be super-simple.
> > > 
> > > But theoretically it should be possible to use a local child_info_spawn
> > > variable at this point. The ch_spawn child_info_spawn instance is not
> > > copied to the child anyway, so that should be safe. The same goes for
> > > posix_spawn() then, btw.
> > > 
> > > I checked the sources and I don't see any dependency to ch_spawn
> > > from a spawning process, in contrast to an exec'ing process. That
> > > doesn't mean there is none, just that I didn't find any.
> > 
> > Thanks!
> > As a starting point, I tried tntroducing locking. It almost works
> > as expected, however, sometimes my STC in my first report is hangs
> > if N is large e.g. 100. The patch is as attached.
> > 
> > What am I missing?
>> I don't know. You're perhaps not releasing the lock in all cases.
> But I would have to debug this just like you ¯\_(ツ)_/¯
>> Out of curiosity, did you try using a locale child_info_spawn instance
> instead? That would be a rather nice solution, but I'm pretty sure
> there's some other problem lurking in the dark...

I'm not sure what to do with local child_info_spawn.
Some of other modules refer to ch_spawn, such as exception.cc and
pinfo.cc. Also, has_execed* uses ch_spawn. What should we do for that?
I've just tried simply the following patch, however, this also hangs
with my STC.

diff --git a/winsup/cygwin/spawn.cc b/winsup/cygwin/spawn.cc
index cb58b6eed..56fca6e45 100644
--- a/winsup/cygwin/spawn.cc
+++ b/winsup/cygwin/spawn.cc
@@ -944,6 +944,7 @@ spawnve (int mode, const char *path, const char *const *argv,
 int ret;
 
 syscall_printf ("spawnve (%s, %s, %p)", path, argv[0], envp);
+ child_info_spawn ch_spawn_local;
 
 if (!envp)
 envp = empty_env;
@@ -951,7 +952,7 @@ spawnve (int mode, const char *path, const char *const *argv,
 switch (_P_MODE (mode))
 {
 case _P_OVERLAY:
- ch_spawn.worker (path, argv, envp, mode);
+ ch_spawn_local.worker (path, argv, envp, mode);
 /* Errno should be set by worker. */
 ret = -1;
 break;
@@ -961,7 +962,7 @@ spawnve (int mode, const char *path, const char *const *argv,
 case _P_WAIT:
 case _P_DETACH:
 case _P_SYSTEM:
- ret = ch_spawn.worker (path, argv, envp, mode);
+ ret = ch_spawn_local.worker (path, argv, envp, mode);
 break;
 default:
 set_errno (EINVAL);
-- 
Takashi Yano <takashi.yano@nifty.ne.jp>
