From 62e33576819ab35b849d7262d0640c66b0d3a839 Mon Sep 17 00:00:00 2001 From: Laurent Pinchart Date: Sun, 6 Oct 2019 07:55:17 +0300 Subject: libcamera: timer: Forbid starting or stopping timer from another thread MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Starting or stopping a timer from a different thread than the one it belongs to is inherently racy. Disallow it. Signed-off-by: Laurent Pinchart Reviewed-by: Niklas Söderlund Reviewed-by: Jacopo Mondi --- src/libcamera/timer.cpp | 24 +++++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-) diff --git a/src/libcamera/timer.cpp b/src/libcamera/timer.cpp index 5d4e5271..8749d66c 100644 --- a/src/libcamera/timer.cpp +++ b/src/libcamera/timer.cpp @@ -36,6 +36,11 @@ LOG_DEFINE_CATEGORY(Timer) * Once started the timer will run until it times out. It can be stopped with * stop(), and once it times out or is stopped, can be started again with * start(). + * + * Timers run in the thread they belong to, and thus emit the \a ref timeout + * signal from that thread. To avoid race conditions they must not be started + * or stopped from a different thread, attempts to do so will be rejected and + * logged, and may cause undefined behaviour. */ /** @@ -57,17 +62,24 @@ Timer::~Timer() * \brief Start or restart the timer with a timeout of \a msec * \param[in] msec The timer duration in milliseconds * - * If the timer is already running it will be stopped and restarted. + * This method shall be called from the thread the timer is associated with. If + * the timer is already running it will be stopped and restarted. */ /** * \brief Start or restart the timer with a timeout of \a duration * \param[in] duration The timer duration in milliseconds * - * If the timer is already running it will be stopped and restarted. + * This method shall be called from the thread the timer is associated with. If + * the timer is already running it will be stopped and restarted. */ void Timer::start(std::chrono::milliseconds duration) { + if (Thread::current() != thread()) { + LOG(Timer, Error) << "Timer can't be started from another thread"; + return; + } + deadline_ = utils::clock::now() + duration; LOG(Timer, Debug) @@ -87,13 +99,19 @@ void Timer::start(std::chrono::milliseconds duration) * After this function returns the timer is guaranteed not to emit the * \ref timeout signal. * - * If the timer is not running this function performs no operation. + * This method shall be called from the thread the timer is associated with. If + * the timer is not running this function performs no operation. */ void Timer::stop() { if (!isRunning()) return; + if (Thread::current() != thread()) { + LOG(Timer, Error) << "Timer can't be stopped from another thread"; + return; + } + unregisterTimer(); } -- cgit v1.2.1