Make thread control POSIX compliant

Closes issue #41109

diff --git a/changes/bug41109 b/changes/bug41109
new file mode 100644 (file)
index 0000000..65d9627
--- /dev/null
+++ b/changes/bug41109
@@ -0,0 +1,3 @@
+  o Minor bugfixes (threads):
+    - Make thread control POSIX compliant.
+      Fixes bug 41109; bugfix on 0.4.8.17-dev.

diff --git a/src/lib/evloop/workqueue.c b/src/lib/evloop/workqueue.c
index 59a6cf13cdc18a845b8259dd9944cd5ff1f34424..f8a5cb87e949122ac3dc58d1ca03661910e0fddb 100644 (file)
--- a/src/lib/evloop/workqueue.c
+++ b/src/lib/evloop/workqueue.c
@@ -38,6 +38,7 @@
 #include "lib/net/alertsock.h"
 #include "lib/net/socket.h"
 #include "lib/thread/threads.h"
+#include "lib/time/compat_time.h"
 
 #include "ext/tor_queue.h"
 #include <event2/event.h>
@@ -278,6 +279,7 @@ static void
 worker_thread_main(void *thread_)
 {
   static int n_worker_threads_running = 0;
+  static unsigned long control_lock_owner = 0;
   workerthread_t *thread = thread_;
   threadpool_t *pool = thread->in_pool;
   workqueue_entry_t *work;
@@ -297,6 +299,14 @@ worker_thread_main(void *thread_)
    * pool->lock must be prelocked here. */
   tor_mutex_acquire(&pool->lock);
 
+  if (control_lock_owner == 0) {
+    /* pool->control_lock stays locked. This is required for the main thread
+     * to wait for the worker threads to exit on shutdown, so the memory
+     * clean up won't begin before all threads have exited. */
+    tor_mutex_acquire(&pool->control_lock);
+    control_lock_owner = tor_get_thread_id();
+  }
+
   log_debug(LD_GENERAL, "Worker thread has entered the work loop [TID: %lu].",
             tor_get_thread_id());
 
@@ -362,11 +372,22 @@ exit:
             pool->n_threads_max - n_worker_threads_running + 1,
             pool->n_threads_max, tor_get_thread_id());
 
-  if (--n_worker_threads_running == 0)
+  if (tor_get_thread_id() == control_lock_owner) {
+    /* Wait for the other worker threads to exit so we
+     * can safely unlock pool->control_lock. */
+    while (n_worker_threads_running > 1) {
+      tor_mutex_release(&pool->lock);
+      tor_sleep_msec(10);
+      tor_mutex_acquire(&pool->lock);
+    }
+
+    tor_mutex_release(&pool->lock);
     /* Let the main thread know, the last worker thread has exited. */
     tor_mutex_release(&pool->control_lock);
-
-  tor_mutex_release(&pool->lock);
+  } else {
+    --n_worker_threads_running;
+    tor_mutex_release(&pool->lock);
+  }
 }
 
 /** Put a reply on the reply queue.  The reply must not currently be on
@@ -623,9 +644,9 @@ check_status:
 
   /* Let worker threads enter the work loop. */
   tor_mutex_release(&pool->lock);
-
-  /* pool->control_lock stays locked. This is required for the main thread
-   * to wait for the worker threads to exit on shutdown. */
+  /* Let one of the worker threads take the ownership of pool->control_lock.
+   * This is required for compliance with POSIX. */
+  tor_mutex_release(&pool->control_lock);
 
   return status;
 }