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switch to use a shared lock with upgrade instead of only a unique lock for message_mutex_ #101

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Apr 21, 2015
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switch to use a shared lock with upgrade instead of only a unique lock for message_mutex_ #101

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24 changes: 18 additions & 6 deletions tf2_ros/include/tf2_ros/message_filter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -277,7 +277,7 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
*/
void clear()
{
boost::mutex::scoped_lock lock(messages_mutex_);
boost::unique_lock< boost::shared_mutex > unique_lock(messages_mutex_);

TF2_ROS_MESSAGEFILTER_DEBUG("%s", "Cleared");

Expand Down Expand Up @@ -359,7 +359,7 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
}
}

boost::mutex::scoped_lock lock(messages_mutex_);

// We can transform already
if (info.success_count == expected_success_count_)
{
Expand All @@ -370,6 +370,9 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
// If this message is about to push us past our queue size, erase the oldest message
if (queue_size_ != 0 && message_count_ + 1 > queue_size_)
{
// While we're using the reference keep a shared lock on the messages.
boost::shared_lock< boost::shared_mutex > shared_lock(messages_mutex_);

++dropped_message_count_;
const MessageInfo& front = messages_.front();
TF2_ROS_MESSAGEFILTER_DEBUG("Removed oldest message because buffer is full, count now %d (frame_id=%s, stamp=%f)", message_count_,
Expand All @@ -383,13 +386,20 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
}

messageDropped(front.event, filter_failure_reasons::Unknown);

// Unlock the shared lock and get a unique lock. Upgradeable lock is used in transformable.
// There can only be one upgrade lock. It's important the cancelTransformableRequest not deadlock with transformable.
// They both require the transformable_requests_mutex_ in BufferCore.
shared_lock.unlock();
// There is a very slight race condition if an older message arrives in this gap.
boost::unique_lock< boost::shared_mutex > unique_lock(messages_mutex_);
messages_.pop_front();
--message_count_;
--message_count_;
}

// Add the message to our list
info.event = evt;
// Lock access to the messages_ before modifying them.
boost::unique_lock< boost::shared_mutex > unique_lock(messages_mutex_);
messages_.push_back(info);
++message_count_;
}
Expand Down Expand Up @@ -456,7 +466,7 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
{
namespace mt = ros::message_traits;

boost::mutex::scoped_lock lock(messages_mutex_);
boost::upgrade_lock< boost::shared_mutex > lock(messages_mutex_);

// find the message this request is associated with
typename L_MessageInfo::iterator msg_it = messages_.begin();
Expand Down Expand Up @@ -519,6 +529,8 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
can_transform = false;
}

// We will be mutating messages now, require unique lock
boost::upgrade_to_unique_lock< boost::shared_mutex > uniqueLock(lock);
if (can_transform)
{
TF2_ROS_MESSAGEFILTER_DEBUG("Message ready in frame %s at time %.3f, count now %d", frame_id.c_str(), stamp.toSec(), message_count_ - 1);
Expand Down Expand Up @@ -678,7 +690,7 @@ class MessageFilter : public MessageFilterBase, public message_filters::SimpleFi
typedef std::list<MessageInfo> L_MessageInfo;
L_MessageInfo messages_;
uint32_t message_count_; ///< The number of messages in the list. Used because <container>.size() may have linear cost
boost::mutex messages_mutex_; ///< The mutex used for locking message list operations
boost::shared_mutex messages_mutex_; ///< The mutex used for locking message list operations
uint32_t expected_success_count_;

bool warned_about_empty_frame_id_;
Expand Down