path: root/src/io.c
diff options
authorLars Henriksen <LarsHenriksen@get2net.dk>2018-07-13 22:40:37 +0200
committerLukas Fleischer <lfleischer@calcurse.org>2018-07-28 14:06:15 +0200
commit5e5370864886c2e813b5335f6ef5cf5648f2ec02 (patch)
treebb5d4d67854e3525f79bf80165effced03ee1ce9 /src/io.c
parent6a6c7117dee91c9fd11c2b30f34f70386f1fba21 (diff)
Solve deadlock in notification bar
calcurse deadlocks when 1) an upcoming appointment is on display in the notification bar, 2) an external command (like help) is started, 3) the time for the upcoming appointment arrives, and 4) the external command is exited. The notification bar thread is stopped while the external command is running. Upon exit from the external command, the n-bar thread is restarted and calcurse locks. The cause is the way in which the main notification bar thread is stopped: static pthread_t notify_t_main; void notify_stop_main_thread(void) { if (notify_t_main) { pthread_cancel(notify_t_main); pthread_join(notify_t_main, NULL); } } Objects of type pthread_t are opaque and should not be accessed directly. Initially notify_t_main is an uninitialised static variable (0), but later it has a value, which may or may not be the thread id of the notification main thread. Note that the thread id after exit of a thread may become the thread id of a new thread. Thus the variable set when the thread is created, is invalid after exit of the thread. Specifically, the first time notify_stop_main_thread() is called (by notify_start_main_thread() before the thread is created) is harmless (because notify_t_main is 0). Calling notify_stop_main_thread() later may be either OK because the main thread is running, or harmless because no thread with id notify_t_main is running: the two functions will fail with return value ESRCH (no such process), or fatal because an unrelated thread with this thread id is running: it will be cancelled, and the join may or may not succeed depending on whether the thread is joinable or detached. The "unrelated thread" could be the next-appointment thread, notify_thread_app, launched by notify_check_next_app(). Always calling notify_stop_main_thread() before starting the main thread becomes fatal when notify_check_next_app() is called shortly before notify_start_main_thread(). This is the case in the scenario described. The next-app-thread is then running when notify_stop_main_thread() is called, and apparently it has the thread id of the old main thread (confirmed by logging the return values from pthread_cancel() and pthread_join(); the first succeeds while the second fails with EINVALID which means that the thread is not joinable). The next-app-thread will therefore exit without unlocking mutexes. Ensure that notify_t_main, in case the notify main thread is not running, has a value that it will never have when it is running. A possibility is the thread id of the main() calcurse process (returned by pthread_self()). Check for this condition in notify_stop_main_thread() and set notify_t_main when the thread is stopped. Similar changes have been introduced for the periodic save thread and the calendar date thread. Signed-off-by: Lars Henriksen <LarsHenriksen@get2net.dk> Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>
Diffstat (limited to 'src/io.c')
1 files changed, 3 insertions, 3 deletions
diff --git a/src/io.c b/src/io.c
index d0c80c5..51adb42 100644
--- a/src/io.c
+++ b/src/io.c
@@ -1501,8 +1501,6 @@ void io_log_free(struct io_file *log)
-static pthread_t io_t_psave;
/* Thread used to periodically save data. */
static void *io_psave_thread(void *arg)
@@ -1524,7 +1522,8 @@ void io_start_psave_thread(void)
/* Stop periodic data saves. */
void io_stop_psave_thread(void)
- if (!io_t_psave)
+ /* Is the thread running? */
+ if (pthread_equal(io_t_psave, pthread_self()))
/* Lock the mutex to avoid cancelling the thread during saving. */
@@ -1532,6 +1531,7 @@ void io_stop_psave_thread(void)
pthread_join(io_t_psave, NULL);
+ io_t_psave = pthread_self();