runtime/cgo: retry pthread_create on EAGAIN for OpenBSD

For reasons that I do not know, OpenBSD does not call pthread_create
directly, but instead looks it up in libpthread.so. That means that we
can't use the code used on other systems to retry pthread_create on
EAGAIN, since that code simply calls pthread_create.

This patch copies that code to an OpenBSD-specific version.

Also, check for an EAGAIN failure in the test, as that seems to be the
underlying cause of the test failure on several systems including OpenBSD.

Fixes #18146.

Change-Id: I3bceaa1e03a7eaebc2da19c9cc146b25b59243ef
Reviewed-on: https://go-review.googlesource.com/33905
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/cgo/test/issue18146.go

@@ -18,14 +18,10 @@ import (
 	"runtime"
 	"syscall"
 	"testing"
+	"time"
 )
 
 func test18146(t *testing.T) {
-	switch runtime.GOOS {
-	case "darwin", "openbsd", "dragonfly":
-		t.Skip("skipping on %s; issue 18146", runtime.GOOS)
-	}
-
 	attempts := 1000
 	threads := 4
 
@@ -64,6 +60,18 @@ func test18146(t *testing.T) {
 		cmd.Stdout = buf
 		cmd.Stderr = buf
 		if err := cmd.Start(); err != nil {
+			// We are starting so many processes that on
+			// some systems (problem seen on Darwin,
+			// Dragonfly, OpenBSD) the fork call will fail
+			// with EAGAIN.
+			if pe, ok := err.(*os.PathError); ok {
+				err = pe.Err
+			}
+			if se, ok := err.(syscall.Errno); ok && se == syscall.EAGAIN {
+				time.Sleep(time.Millisecond)
+				continue
+			}
+
 			t.Error(err)
 			return
 		}

src/runtime/cgo/gcc_libinit_openbsd.c

@@ -2,6 +2,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+#include <sys/types.h>
+#include <errno.h>
+#include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include "libcgo.h"
@@ -48,3 +51,24 @@ void x_cgo_set_context_function(void (*context)(struct context_arg*)) {
 void (*(_cgo_get_context_function(void)))(struct context_arg*) {
 	return cgo_context_function;
 }
+
+// _cgo_try_pthread_create retries sys_pthread_create if it fails with
+// EAGAIN.
+int
+_cgo_openbsd_try_pthread_create(int (*sys_pthread_create)(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*),
+	pthread_t* thread, const pthread_attr_t* attr, void* (*pfn)(void*), void* arg) {
+	int tries;
+	int err;
+	struct timespec ts;
+
+	for (tries = 0; tries < 100; tries++) {
+		err = sys_pthread_create(thread, attr, pfn, arg);
+		if (err != EAGAIN) {
+			return err;
+		}
+		ts.tv_sec = 0;
+		ts.tv_nsec = (tries + 1) * 1000 * 1000; // Milliseconds.
+		nanosleep(&ts, nil);
+	}
+	return EAGAIN;
+}

src/runtime/cgo/gcc_openbsd_386.c

@@ -9,6 +9,7 @@
 #include <signal.h>
 #include <string.h>
 #include "libcgo.h"
+#include "libcgo_unix.h"
 
 static void* threadentry(void*);
 static void (*setg_gcc)(void*);
@@ -170,7 +171,7 @@ _cgo_sys_thread_start(ThreadStart *ts)
 
 	// Leave stacklo=0 and set stackhi=size; mstack will do the rest.
 	ts->g->stackhi = size;
-	err = sys_pthread_create(&p, &attr, threadentry, ts);
+	err = _cgo_openbsd_try_pthread_create(sys_pthread_create, &p, &attr, threadentry, ts);
 
 	pthread_sigmask(SIG_SETMASK, &oset, nil);
 

src/runtime/cgo/gcc_openbsd_amd64.c

@@ -9,6 +9,7 @@
 #include <signal.h>
 #include <string.h>
 #include "libcgo.h"
+#include "libcgo_unix.h"
 
 static void* threadentry(void*);
 static void (*setg_gcc)(void*);
@@ -170,7 +171,7 @@ _cgo_sys_thread_start(ThreadStart *ts)
 
 	// Leave stacklo=0 and set stackhi=size; mstack will do the rest.
 	ts->g->stackhi = size;
-	err = sys_pthread_create(&p, &attr, threadentry, ts);
+	err = _cgo_openbsd_try_pthread_create(sys_pthread_create, &p, &attr, threadentry, ts);
 
 	pthread_sigmask(SIG_SETMASK, &oset, nil);
 

src/runtime/cgo/libcgo_unix.h

@@ -5,4 +5,11 @@
 /*
  * Call pthread_create, retrying on EAGAIN.
  */
-int _cgo_try_pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*);
+extern int _cgo_try_pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*);
+
+/*
+ * Same as _cgo_try_pthread_create, but passing on the pthread_create function.
+ * Only defined on OpenBSD.
+ */
+extern int _cgo_openbsd_try_pthread_create(int (*)(pthread_t*, const pthread_attr_t*, void *(*pfn)(void*), void*),
+	pthread_t*, const pthread_attr_t*, void* (*)(void*), void* arg);