Hi Ken,
On Jul 30 13:59, Corinna Vinschen wrote:
> On Jul 29 19:12, Ken Brown via Cygwin wrote:
> > On 7/29/2020 4:17 PM, Ken Brown via Cygwin wrote:
> > > posix_spawn(p) returns before the spawned process is fully up and
> > > running. [...]
> > I just took a look at the source, and I see that posix_spawn was taken from
> > FreeBSD. Does FreeBSD have the same problem? Should applications just be
> > aware of this issue and insert a sleep after posix_spawn before sending
> > signals?
>
> Actually, this is a Cygwin problem. I just had a look into the
> newlib implementation myself, and it turns out that the code,
> in particular the do_posix_spawn() function, is BSD specific. It
> relies on the BSD implementation of vfork(2). Cygwin's vfork(2)
> on the other hand, is NOT following the historic idea of the
> BSD vfork(2), rather it's equivalent to fork(2). This is
> POSIX compliant, but certainly the reliance of the BSD vfork
> behaviour makes do_posix_spawn() as it's implemented right now,
> not overly functional for Cygwin.
>
> IOW, we need a Cygwin-specific do_posix_spawn() using fork(2)
> in conjunction with some synchronization the BSD function
> gets "for free" by using its specific vfork(2).
Below is a POC implementation for a Cygwin-specific do_posix_spawn().
If this does the trick (at least your testcase works in my testing),
then I'm planning to move the function over to the winsup/cygwin dir
so it can be streamlined further.
Can you give it a try?
Thanks,
Corinna
diff --git a/newlib/libc/posix/posix_spawn.c b/newlib/libc/posix/posix_spawn.c
index 19c5cd0fe986..3adbac29d7fd 100644
--- a/newlib/libc/posix/posix_spawn.c
+++ b/newlib/libc/posix/posix_spawn.c
@@ -254,6 +254,82 @@ process_file_actions(const posix_spawn_file_actions_t fa)
return (0);
}
+#ifdef __CYGWIN__
+#include <windows.h>
+#include <sys/mman.h>
+#include <process.h>
+
+typedef struct
+{
+ pid_t pid;
+ int error;
+} child_info;
+
+static int
+do_posix_spawn(pid_t *pid, const char *path,
+ const posix_spawn_file_actions_t *fa,
+ const posix_spawnattr_t *sa,
+ char * const argv[], char * const envp[], int use_env_path)
+{
+ pid_t p;
+ int ret = 0;
+ child_info *ci;
+
+ ci = (child_info *) mmap(NULL, sizeof(child_info),
+ PROT_READ | PROT_WRITE,
+ MAP_SHARED | MAP_ANONYMOUS, -1, 0);
+ if (ci == MAP_FAILED)
+ return (errno);
+
+ /* Cygwin's vfork does not follow BSD vfork semantics. Rather it's
+ equivalent to fork. While that's POSIX compliant, it means the
+ below FreeBSD implementation relying on BSD vfork semantics
+ doesn't work as expected on Cygwin. */
+ p = fork();
+ switch (p) {
+ case -1:
+ ret = errno;
+ break;
+ case 0:
+ if (sa != NULL) {
+ ci->error = process_spawnattr(*sa);
+ if (ci->error)
+ _exit(127);
+ }
+ if (fa != NULL) {
+ ci->error = process_file_actions(*fa);
+ if (ci->error)
+ _exit(127);
+ }
+ if (use_env_path)
+ p = spawnvpe(_P_NOWAITO, path,
+ (const char * const *) argv,
+ (const char * const *)
+ (envp != NULL ? envp : *p_environ));
+ else
+ p = spawnve(_P_NOWAITO, path,
+ (const char * const *) argv,
+ (const char * const *)
+ (envp != NULL ? envp : *p_environ));
+ if (p < 0) {
+ ci->error = errno;
+ _exit(127);
+ }
+ ci->pid = p;
+ _exit (0);
+ default:
+ if (waitpid(p, NULL, 0) < 0)
+ ret = errno;
+ else if (ci->error)
+ ret = ci->error;
+ else if (pid != NULL)
+ *pid = ci->pid;
+ break;
+ }
+ munmap(ci, sizeof(child_info));
+ return ret;
+}
+#else
static int
do_posix_spawn(pid_t *pid, const char *path,
const posix_spawn_file_actions_t *fa,
@@ -292,6 +368,7 @@ do_posix_spawn(pid_t *pid, const char *path,
return (error);
}
}
+#endif
int
posix_spawn (pid_t *pid,
--
Corinna Vinschen
Cygwin Maintainer
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