[dpdk-dev] [RFC] eal: simplify the implementation of rte_ctrl_thread_create

[Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>]

The current described behaviour of rte_ctrl_thread_create is
rigid which makes the implementation of the function complex.
The behavior is abstracted to allow for simplified implementation.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
---
 lib/eal/common/eal_common_thread.c | 65 +++++++++++++-----------------
 lib/eal/include/rte_lcore.h        |  8 ++--
 2 files changed, 32 insertions(+), 41 deletions(-)

diff --git a/lib/eal/common/eal_common_thread.c b/lib/eal/common/eal_common_thread.c
index 1a52f42a2b..86cacd840c 100644
--- a/lib/eal/common/eal_common_thread.c
+++ b/lib/eal/common/eal_common_thread.c
@@ -169,35 +169,35 @@ __rte_thread_uninit(void)
 struct rte_thread_ctrl_params {
 	void *(*start_routine)(void *);
 	void *arg;
-	pthread_barrier_t configured;
-	unsigned int refcnt;
+	int ret;
+	/* Synchronization variable between the control thread
+	 * and the thread calling rte_ctrl_thread_create function.
+	 * 0 - Initialized
+	 * 1 - Control thread is running successfully
+	 * 2 - Control thread encountered an error. 'ret' has the
+	 *     error code.
+	 */
+	unsigned int sync;
 };
 
-static void ctrl_params_free(struct rte_thread_ctrl_params *params)
-{
-	if (__atomic_sub_fetch(&params->refcnt, 1, __ATOMIC_ACQ_REL) == 0) {
-		(void)pthread_barrier_destroy(&params->configured);
-		free(params);
-	}
-}
-
 static void *ctrl_thread_init(void *arg)
 {
 	struct internal_config *internal_conf =
 		eal_get_internal_configuration();
 	rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
 	struct rte_thread_ctrl_params *params = arg;
-	void *(*start_routine)(void *);
+	void *(*start_routine)(void *) = params->start_routine;
 	void *routine_arg = params->arg;
 
 	__rte_thread_init(rte_lcore_id(), cpuset);
-
-	pthread_barrier_wait(&params->configured);
-	start_routine = params->start_routine;
-	ctrl_params_free(params);
-
-	if (start_routine == NULL)
+	params->ret = pthread_setaffinity_np(pthread_self(),
+				sizeof(*cpuset), cpuset);
+	if (params->ret != 0) {
+		params->sync = 2;
 		return NULL;
+	}
+
+	params->sync = 1;
 
 	return start_routine(routine_arg);
 }
@@ -207,9 +207,6 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 		const pthread_attr_t *attr,
 		void *(*start_routine)(void *), void *arg)
 {
-	struct internal_config *internal_conf =
-		eal_get_internal_configuration();
-	rte_cpuset_t *cpuset = &internal_conf->ctrl_cpuset;
 	struct rte_thread_ctrl_params *params;
 	int ret;
 
@@ -219,15 +216,12 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 
 	params->start_routine = start_routine;
 	params->arg = arg;
-	params->refcnt = 2;
-
-	ret = pthread_barrier_init(&params->configured, NULL, 2);
-	if (ret != 0)
-		goto fail_no_barrier;
+	params->ret = 0;
+	params->sync = 0;
 
 	ret = pthread_create(thread, attr, ctrl_thread_init, (void *)params);
 	if (ret != 0)
-		goto fail_with_barrier;
+		goto thread_create_failed;
 
 	if (name != NULL) {
 		ret = rte_thread_setname(*thread, name);
@@ -236,24 +230,21 @@ rte_ctrl_thread_create(pthread_t *thread, const char *name,
 				"Cannot set name for ctrl thread\n");
 	}
 
-	ret = pthread_setaffinity_np(*thread, sizeof(*cpuset), cpuset);
-	if (ret != 0)
-		params->start_routine = NULL;
+	/* Wait for the control thread to initialize successfully */
+	while (!params->sync)
+		rte_pause();
+	ret = params->ret;
 
-	pthread_barrier_wait(&params->configured);
-	ctrl_params_free(params);
+	free(params);
 
-	if (ret != 0)
-		/* start_routine has been set to NULL above; */
-		/* ctrl thread will exit immediately */
+	if (params->sync != 1)
+		/* ctrl thread is exiting */
 		pthread_join(*thread, NULL);
 
 	return -ret;
 
-fail_with_barrier:
-	(void)pthread_barrier_destroy(&params->configured);
+thread_create_failed:
 
-fail_no_barrier:
 	free(params);
 
 	return -ret;
diff --git a/lib/eal/include/rte_lcore.h b/lib/eal/include/rte_lcore.h
index 1550b75da0..f1cc5e38dc 100644
--- a/lib/eal/include/rte_lcore.h
+++ b/lib/eal/include/rte_lcore.h
@@ -420,10 +420,10 @@ rte_thread_unregister(void);
 /**
  * Create a control thread.
  *
- * Wrapper to pthread_create(), pthread_setname_np() and
- * pthread_setaffinity_np(). The affinity of the new thread is based
- * on the CPU affinity retrieved at the time rte_eal_init() was called,
- * the dataplane and service lcores are then excluded.
+ * Creates a control thread with the given name and attributes. The
+ * affinity of the new thread is based on the CPU affinity retrieved
+ * at the time rte_eal_init() was called, the dataplane and service
+ * lcores are then excluded.
  *
  * @param thread
  *   Filled with the thread id of the new created thread.
-- 
2.17.1