CDRIVER-3757 inits pool cond, adds test (#666)

Initializes pool condition variable.  Adds (non-deterministic) test for the case where a thread is waiting in call to `mongoc_client_pool_pop` for a client to become available.

Author: Andrew Witten

src/libmongoc/src/mongoc/mongoc-client-pool.c

@@ -117,6 +117,7 @@ mongoc_client_pool_new (const mongoc_uri_t *uri)
 
    pool = (mongoc_client_pool_t *) bson_malloc0 (sizeof *pool);
    bson_mutex_init (&pool->mutex);
+   mongoc_cond_init (&pool->cond);
    _mongoc_queue_init (&pool->queue);
    pool->uri = mongoc_uri_copy (uri);
    pool->min_pool_size = 0;

src/libmongoc/tests/test-mongoc-client-pool.c

@@ -405,6 +405,68 @@ test_client_pool_create_unused_session (void *context)
    ASSERT_NO_CAPTURED_LOGS ("mongoc_client_pool_destroy");
 }
 
+
+/* Tests case where thread is blocked waiting for a client to be pushed back
+ * into the client pool.  Specifically this tests that the program terminates.
+ * Addresses CDRIVER-3757 */
+typedef struct pool_timeout {
+   mongoc_client_pool_t *pool;
+   bson_mutex_t mutex;
+   mongoc_cond_t cond;
+   int nleft;
+} pool_timeout_args_t;
+
+static BSON_THREAD_FUN (worker, arg)
+{
+   pool_timeout_args_t *args = arg;
+   mongoc_client_t *client = mongoc_client_pool_pop (args->pool);
+   BSON_ASSERT (client);
+   _mongoc_usleep (10);
+   mongoc_client_pool_push (args->pool, client);
+   bson_mutex_lock (&args->mutex);
+   /* notify main thread that current thread has terminated */
+   args->nleft--;
+   mongoc_cond_signal (&args->cond);
+   bson_mutex_unlock (&args->mutex);
+   BSON_THREAD_RETURN;
+}
+
+static void
+test_client_pool_max_pool_size_exceeded (void)
+{
+   mongoc_client_pool_t *pool;
+   mongoc_uri_t *uri;
+   bson_thread_t thread1, thread2;
+   pool_timeout_args_t *args = bson_malloc0 (sizeof (pool_timeout_args_t));
+   int wait_time = 4000; /* 4000 msec = 4 sec */
+   int ret;
+
+   uri = mongoc_uri_new ("mongodb://127.0.0.1/?maxpoolsize=1");
+   pool = mongoc_client_pool_new (uri);
+   args->pool = pool;
+   args->nleft = 2;
+   bson_mutex_init (&args->mutex);
+   mongoc_cond_init (&args->cond);
+
+   COMMON_PREFIX (thread_create) (&thread1, worker, args);
+   COMMON_PREFIX (thread_create) (&thread2, worker, args);
+
+   bson_mutex_lock (&args->mutex);
+   while (args->nleft > 0) {
+      ret = mongoc_cond_timedwait (&args->cond, &args->mutex, wait_time);
+      /* ret non-zero indicates an error (a timeout) */
+      BSON_ASSERT (!ret);
+   }
+   bson_mutex_unlock (&args->mutex);
+
+   COMMON_PREFIX (thread_join) (thread1);
+   COMMON_PREFIX (thread_join) (thread2);
+
+   mongoc_uri_destroy (uri);
+   mongoc_client_pool_destroy (pool);
+   bson_free (args);
+}
+
 void
 test_client_pool_install (TestSuite *suite)
 {
@@ -440,4 +502,7 @@ test_client_pool_install (TestSuite *suite)
    TestSuite_AddLive (suite,
                       "/ClientPool/destroy_without_push",
                       test_client_pool_destroy_without_pushing);
+   TestSuite_AddLive (suite,
+                      "/ClientPool/max_pool_size_exceeded",
+                      test_client_pool_max_pool_size_exceeded);
 }