On Tue, 13 May 2025 09:13:58 GMT, Aleksey Shipilev <sh...@openjdk.org> wrote:
>> src/java.base/unix/native/libjava/ProcessImpl_md.c line 377:
>>
>>> 375: throwIOExceptionImpl(env, errnum, defaultDetail, "");
>>> 376: }
>>> 377: }
>>
>> Why only for POSIX_SPAWN? We use jspawnhelper also for fork/vfork+exec.
>
> Er? This is news to me. Where do you see this? I see we only pass the
> `helperpath` (carrying `jspawnhelper` path only to `POSIX_SPAWN` mode:
>
>
> static pid_t
> startChild(JNIEnv *env, jobject process, ChildStuff *c, const char
> *helperpath) {
> switch (c->mode) {
> /* vfork(2) is deprecated on Darwin*/
> #ifndef __APPLE__
> case MODE_VFORK:
> return vforkChild(c);
> #endif
> case MODE_FORK:
> return forkChild(c);
> case MODE_POSIX_SPAWN:
> return spawnChild(env, process, c, helperpath);
> default:
> return -1;
> }
> }
You are right and I am confused. I always assumed that the primary function of
jspawnhelper was to make vfork safe. Historically, that was the typical reason
for an intermediate exec() to a helper - basically, you first exec() the helper
as quickly as possible to get your own process memory. Then you do all the
things you need to do in preparation for the final exec(), then exec again.
I am surprised that this has worked with vfork() so flawlessly all this time.
Maybe it didn't; maybe the libc's have all internally replaced vfork() with
fork(), since fork() is fast enough nowadays.
I actually don't understand why the jspawnhelper is even needed for
posix_spawn, since all the things one does in jspawnhelper can be done also via
posix_spawn process attributes.
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PR Review Comment: https://git.openjdk.org/jdk/pull/24149#discussion_r2086739029
