sessiond: transition session_list synchronization from pthread to std

In order to allow the use of RAII to manage the locking in the client command
handler (process_client_msg), the session list's synchronization primitives are
changed to use those of libstd.

No change in behavior is intended by this change.

Change-Id: I6367e25557b05e16a48436304791cd7a37dc8904
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

diff --git a/src/bin/lttng-sessiond/main.cpp b/src/bin/lttng-sessiond/main.cpp
index bfd53e7e47041818996b55d9bb15266901688ebf..16d0721c1a27d455b16d96ed11a05ba1cf4aced4 100644 (file)
--- a/src/bin/lttng-sessiond/main.cpp
+++ b/src/bin/lttng-sessiond/main.cpp
@@ -277,7 +277,6 @@ static void wait_consumer(struct consumer_data *consumer_data)
 static void sessiond_cleanup()
 {
        int ret;
-       struct ltt_session_list *session_list = session_get_list();
 
        DBG("Cleanup sessiond");
 
@@ -327,8 +326,6 @@ static void sessiond_cleanup()
        DBG("Removing directory %s", the_config.consumerd64_path.value);
        (void) rmdir(the_config.consumerd64_path.value);
 
-       pthread_mutex_destroy(&session_list->lock);
-
        DBG("Cleaning up all per-event notifier domain agents");
        agent_by_event_notifier_domain_ht_destroy();
 

diff --git a/src/bin/lttng-sessiond/session.cpp b/src/bin/lttng-sessiond/session.cpp
index ccd4221a242d858be5201237e84fb12f503a64a2..3c9f787dd59601bc2603e5fdf4c5523f86e57125 100644 (file)
--- a/src/bin/lttng-sessiond/session.cpp
+++ b/src/bin/lttng-sessiond/session.cpp
@@ -68,12 +68,7 @@ struct lttng_ht *ltt_sessions_ht_by_name = nullptr;
  *
  * Please see session.h for more explanation and correct usage of the list.
  */
-struct ltt_session_list the_session_list = {
-       .lock = PTHREAD_MUTEX_INITIALIZER,
-       .removal_cond = PTHREAD_COND_INITIALIZER,
-       .next_uuid = 0,
-       .head = CDS_LIST_HEAD_INIT(the_session_list.head),
-};
+struct ltt_session_list the_session_list;
 } /* namespace */
 
 /*
@@ -148,11 +143,11 @@ struct ltt_session_list *session_get_list()
  */
 void session_list_wait_empty()
 {
-       pthread_mutex_lock(&the_session_list.lock);
-       while (!cds_list_empty(&the_session_list.head)) {
-               pthread_cond_wait(&the_session_list.removal_cond, &the_session_list.lock);
-       }
-       pthread_mutex_unlock(&the_session_list.lock);
+       std::unique_lock<std::mutex> list_lock(the_session_list.lock);
+
+       /* Keep waiting until the session list is empty. */
+       the_session_list.removal_cond.wait(list_lock,
+                                          [] { return cds_list_empty(&the_session_list.head); });
 }
 
 /*
@@ -160,7 +155,7 @@ void session_list_wait_empty()
  */
 void session_lock_list() noexcept
 {
-       pthread_mutex_lock(&the_session_list.lock);
+       the_session_list.lock.lock();
 }
 
 /*
@@ -168,7 +163,8 @@ void session_lock_list() noexcept
  */
 int session_trylock_list() noexcept
 {
-       return pthread_mutex_trylock(&the_session_list.lock);
+       /* Return 0 if successfully acquired. */
+       return the_session_list.lock.try_lock() ? 0 : 1;
 }
 
 /*
@@ -176,7 +172,7 @@ int session_trylock_list() noexcept
  */
 void session_unlock_list() noexcept
 {
-       pthread_mutex_unlock(&the_session_list.lock);
+       the_session_list.lock.unlock();
 }
 
 /*
@@ -990,7 +986,7 @@ static void session_release(struct urcu_ref *ref)
        pthread_mutex_destroy(&session->lock);
 
        if (session_published) {
-               ASSERT_LOCKED(the_session_list.lock);
+               ASSERT_SESSION_LIST_LOCKED();
                del_session_list(session);
                del_session_ht(session);
        }
@@ -1011,11 +1007,12 @@ static void session_release(struct urcu_ref *ref)
        free(session);
        if (session_published) {
                /*
-                * Broadcast after free-ing to ensure the memory is
-                * reclaimed before the main thread exits.
+                * Notify after free-ing to ensure the memory is
+                * reclaimed before the main thread exits (and prevent memory leak
+                * reports).
                 */
-               ASSERT_LOCKED(the_session_list.lock);
-               pthread_cond_broadcast(&the_session_list.removal_cond);
+               ASSERT_SESSION_LIST_LOCKED();
+               the_session_list.removal_cond.notify_all();
        }
 }
 
@@ -1040,7 +1037,7 @@ void session_put(struct ltt_session *session)
         * The session list lock must be held as any session_put()
         * may cause the removal of the session from the session_list.
         */
-       ASSERT_LOCKED(the_session_list.lock);
+       ASSERT_SESSION_LIST_LOCKED();
        LTTNG_ASSERT(session->ref.refcount);
        urcu_ref_put(&session->ref, session_release);
 }
@@ -1109,7 +1106,7 @@ struct ltt_session *session_find_by_name(const char *name)
        struct ltt_session *iter;
 
        LTTNG_ASSERT(name);
-       ASSERT_LOCKED(the_session_list.lock);
+       ASSERT_SESSION_LIST_LOCKED();
 
        DBG2("Trying to find session by name %s", name);
 
@@ -1136,7 +1133,7 @@ struct ltt_session *session_find_by_id(uint64_t id)
        struct ltt_session *ls;
 
        ASSERT_RCU_READ_LOCKED();
-       ASSERT_LOCKED(the_session_list.lock);
+       ASSERT_SESSION_LIST_LOCKED();
 
        if (!ltt_sessions_ht_by_id) {
                goto end;
@@ -1168,7 +1165,7 @@ session_create(const char *name, uid_t uid, gid_t gid, struct ltt_session **out_
        enum lttng_error_code ret_code;
        struct ltt_session *new_session = nullptr;
 
-       ASSERT_LOCKED(the_session_list.lock);
+       ASSERT_SESSION_LIST_LOCKED();
        if (name) {
                struct ltt_session *clashing_session;
 
@@ -1363,7 +1360,7 @@ int session_reset_rotation_state(ltt_session& session, enum lttng_rotation_state
 {
        int ret = 0;
 
-       ASSERT_LOCKED(the_session_list.lock);
+       ASSERT_SESSION_LIST_LOCKED();
        ASSERT_LOCKED(session.lock);
 
        session.rotation_state = result;

diff --git a/src/bin/lttng-sessiond/session.hpp b/src/bin/lttng-sessiond/session.hpp
index f5f8ae7bcca08dd06002097c2f988292d8bbcfe7..689b4c1e5ad9c20d93e76baa9dd06bdfd3546e1e 100644 (file)
--- a/src/bin/lttng-sessiond/session.hpp
+++ b/src/bin/lttng-sessiond/session.hpp
@@ -21,7 +21,9 @@
 #include <lttng/lttng-error.h>
 #include <lttng/rotation.h>
 
+#include <condition_variable>
 #include <limits.h>
+#include <mutex>
 #include <stdbool.h>
 #include <urcu/list.h>
 
@@ -54,21 +56,21 @@ struct ltt_session_list {
         * functions are used, the lock MUST be acquired in order to
         * iterate or/and do any actions on that list.
         */
-       pthread_mutex_t lock;
+       std::mutex lock;
        /*
         * This condition variable is signaled on every removal from
         * the session list.
         */
-       pthread_cond_t removal_cond;
+       std::condition_variable removal_cond;
 
        /*
         * Session unique ID generator. The session list lock MUST be
         * upon update and read of this counter.
         */
-       uint64_t next_uuid;
+       uint64_t next_uuid = 0;
 
        /* Linked list head */
-       struct cds_list_head head;
+       struct cds_list_head head = CDS_LIST_HEAD_INIT(head);
 };
 
 /*