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uORBDeviceNode: use px4::atomic instead of volatile for _generation

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_generation is read in a multi-threaded context w/o locking.
This commit is contained in:
Beat Küng
2019-11-20 08:15:34 +01:00
committed by Daniel Agar
parent d648d52ac3
commit 0f6f795aca
2 changed files with 13 additions and 10 deletions
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src/modules/uORB/uORBDeviceNode.cpp
+10 -8
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@@ -168,14 +168,15 @@ uORB::DeviceNode::copy_locked(void *dst, unsigned &generation)
bool updated = false;
if ((dst != nullptr) && (_data != nullptr)) {
unsigned current_generation = _generation.load();
if (_generation > generation + _queue_size) {
if (current_generation > generation + _queue_size) {
// Reader is too far behind: some messages are lost
_lost_messages += _generation - (generation + _queue_size);
generation = _generation - _queue_size;
_lost_messages += current_generation - (generation + _queue_size);
generation = current_generation - _queue_size;
}
if ((_generation == generation) && (generation > 0)) {
if ((current_generation == generation) && (generation > 0)) {
/* The subscriber already read the latest message, but nothing new was published yet.
* Return the previous message
*/
@@ -184,7 +185,7 @@ uORB::DeviceNode::copy_locked(void *dst, unsigned &generation)
memcpy(dst, _data + (_meta->o_size * (generation % _queue_size)), _meta->o_size);
if (generation < _generation) {
if (generation < current_generation) {
++generation;
}
@@ -297,12 +298,13 @@ uORB::DeviceNode::write(cdev::file_t *filp, const char *buffer, size_t buflen)
/* Perform an atomic copy. */
ATOMIC_ENTER;
memcpy(_data + (_meta->o_size * (_generation % _queue_size)), buffer, _meta->o_size);
/* wrap-around happens after ~49 days, assuming a publisher rate of 1 kHz */
unsigned generation = _generation.fetch_add(1);
memcpy(_data + (_meta->o_size * (generation % _queue_size)), buffer, _meta->o_size);
/* update the timestamp and generation count */
_last_update = hrt_absolute_time();
/* wrap-around happens after ~49 days, assuming a publisher rate of 1 kHz */
_generation++;
_published = true;