add src/deadlock_debug_helper.cpp

src/CMakeLists.txt

@@ -68,6 +68,7 @@ add_library(PYSTON_OBJECTS OBJECT ${OPTIONAL_SRCS}
 		core/stats.cpp
 		core/threading.cpp
 		core/util.cpp
+		deadlock_debug_helper.cpp
 		gc/collector.cpp
 		gc/gc_alloc.cpp
 		gc/heap.cpp

src/deadlock_debug_helper.cpp

+// Copyright (c) 2014-2015 Dropbox, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// This file is a hack for debugging deadlocks. It makes pthread_mutex_lock() complain if it takes more than given time
+// (TIMEOUT_S) to grab a lock. Perhaps it will be useful in future.
+
+#if 0 // set to 1 to enable
+
+#include <errno.h>
+#include <pthread.h>
+#include <string.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "core/common.h"
+
+#define TIMEOUT_S 2
+
+extern "C" int pthread_mutex_lock(pthread_mutex_t* lock) {
+    struct timespec timeout;
+    memset(&timeout, 0, sizeof timeout);
+    timeout.tv_sec = TIMEOUT_S;
+
+    pid_t tid = syscall(SYS_gettid);
+    RELEASE_ASSERT(tid > 1, "negative or invalid TID");
+
+    time_t started = time(NULL);
+    RELEASE_ASSERT(started != (time_t)-1, "could not get time()");
+
+    int err;
+    for (;;) {
+        err = pthread_mutex_timedlock(lock, &timeout);
+        if (err != ETIMEDOUT)
+            break;
+        time_t now = time(NULL);
+        RELEASE_ASSERT(now != (time_t)-1, "could not get time()");
+        if (now - started >= TIMEOUT_S) {
+            printf("%d: mutex %p TIMED OUT\n", tid, (void*)lock);
+            started = now;
+        }
+    }
+    RELEASE_ASSERT(!err, "could not lock mutex, error %d", err);
+    return err;
+}
+
+#endif