From 62e33576819ab35b849d7262d0640c66b0d3a839 Mon Sep 17 00:00:00 2001
From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Date: Sun, 6 Oct 2019 07:55:17 +0300
Subject: libcamera: timer: Forbid starting or stopping timer from another
thread
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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 <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>
---
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();
}
--
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