logd: single std::mutex for locking log buffers and tracking readers
There are only three places where the log buffer lock is not already
held when the reader lock is taken:
1) In LogReader, when a new reader connects
2) In LogReader, when a misbehaving reader disconnects
3) LogReaderThread::ThreadFunction()
1) and 2) happen sufficiently rarely that there's no impact if they
additionally held a global lock.
3) is refactored in this CL. Previously, it would do the below in a loop
1) Lock the reader lock then wait on a condition variable
2) Unlock the reader lock
3) Lock the log buffer lock in LogBuffer::FlushTo()
4) In each iteration in the LogBuffer::FlushTo() loop
1) Lock then unlock the reader lock in FilterSecondPass()
2) Unlock the log buffer lock to send the message, then re-lock it
5) Unlock the log buffer lock when leaving LogBuffer::FlushTo()
If these locks are collapsed into a single lock, then this simplifies to:
1) Lock the single lock then wait on a condition variable
2) In each iteration in the LogBuffer::FlushTo() loop
1) Unlock the single lock to send the message, then re-lock it
Collapsing both these locks into a single lock simplifes the code and
removes the overhead of acquiring the second lock, in the majority of
use cases where the first lock is already held.
Secondly, this lock will be a plain std::mutex instead of a RwLock.
RwLock's are appropriate when there is a substantial imbalance between
readers and writers and high contention, neither are true for logd.
Bug: 169736426
Test: logging unit tests
Change-Id: Ia511506f2d0935a5321c1b2f65569066f91ecb06
diff --git a/logd/SerializedLogBuffer.h b/logd/SerializedLogBuffer.h
index 9164526..239a81e 100644
--- a/logd/SerializedLogBuffer.h
+++ b/logd/SerializedLogBuffer.h
@@ -30,9 +30,9 @@
#include "LogReaderList.h"
#include "LogStatistics.h"
#include "LogTags.h"
+#include "LogdLock.h"
#include "SerializedLogChunk.h"
#include "SerializedLogEntry.h"
-#include "rwlock.h"
class SerializedLogBuffer final : public LogBuffer {
public:
@@ -41,11 +41,12 @@
int Log(log_id_t log_id, log_time realtime, uid_t uid, pid_t pid, pid_t tid, const char* msg,
uint16_t len) override;
- std::unique_ptr<FlushToState> CreateFlushToState(uint64_t start, LogMask log_mask) override;
- void DeleteFlushToState(std::unique_ptr<FlushToState> state) override;
+ std::unique_ptr<FlushToState> CreateFlushToState(uint64_t start, LogMask log_mask)
+ REQUIRES(logd_lock) override;
bool FlushTo(LogWriter* writer, FlushToState& state,
const std::function<FilterResult(log_id_t log_id, pid_t pid, uint64_t sequence,
- log_time realtime)>& filter) override;
+ log_time realtime)>& filter)
+ REQUIRES(logd_lock) override;
bool Clear(log_id_t id, uid_t uid) override;
size_t GetSize(log_id_t id) override;
@@ -55,20 +56,19 @@
private:
bool ShouldLog(log_id_t log_id, const char* msg, uint16_t len);
- void MaybePrune(log_id_t log_id) REQUIRES(lock_);
- void Prune(log_id_t log_id, size_t bytes_to_free, uid_t uid) REQUIRES(lock_);
+ void MaybePrune(log_id_t log_id) REQUIRES(logd_lock);
+ void Prune(log_id_t log_id, size_t bytes_to_free, uid_t uid) REQUIRES(logd_lock);
void NotifyReadersOfPrune(log_id_t log_id, const std::list<SerializedLogChunk>::iterator& chunk)
- REQUIRES(reader_list_->reader_threads_lock());
+ REQUIRES(logd_lock);
void RemoveChunkFromStats(log_id_t log_id, SerializedLogChunk& chunk);
- size_t GetSizeUsed(log_id_t id) REQUIRES(lock_);
+ size_t GetSizeUsed(log_id_t id) REQUIRES(logd_lock);
LogReaderList* reader_list_;
LogTags* tags_;
LogStatistics* stats_;
- size_t max_size_[LOG_ID_MAX] GUARDED_BY(lock_) = {};
- std::list<SerializedLogChunk> logs_[LOG_ID_MAX] GUARDED_BY(lock_);
- RwLock lock_;
+ size_t max_size_[LOG_ID_MAX] GUARDED_BY(logd_lock) = {};
+ std::list<SerializedLogChunk> logs_[LOG_ID_MAX] GUARDED_BY(logd_lock);
std::atomic<uint64_t> sequence_ = 1;
};