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[core] Add a shared mutex class #2981

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merged 11 commits into from
Aug 1, 2024
Merged

[core] Add a shared mutex class #2981

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59b5661
[core] Add a shared mutex class
yomnes0 Jul 11, 2024
4d55fa5
[core] Improved syntax of SharedMutex class
yomnes0 Jul 15, 2024
7dc9d62
[core] Removed SRT_ATTR_XXX from SharedLock
yomnes0 Jul 15, 2024
deeb9c9
[core] Fix syntax
yomnes0 Jul 29, 2024
58d575f
[core] Handle spurious wake up in shared mutex locking functions
yomnes0 Jul 30, 2024
d7a24bc
[core] More syntax adjustements
yomnes0 Jul 30, 2024
89f76fe
[core] Removed mutex from getReaderCount, add const attribute
yomnes0 Jul 31, 2024
edf9aa5
[core] Add a mutable qualifier to m_Mutex from SharedMutex
yomnes0 Jul 31, 2024
06e15cf
Apply suggestions from code review
maxsharabayko Aug 1, 2024
6497a50
Removed unnecessary condition signaling.
maxsharabayko Aug 1, 2024
d69f848
Improved the TODO comment.
maxsharabayko Aug 1, 2024
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75 changes: 75 additions & 0 deletions srtcore/sync.h
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Original file line number Diff line number Diff line change
Expand Up @@ -943,6 +943,81 @@ CUDTException& GetThreadLocalError();
/// @param[in] maxVal maximum allowed value of the resulting random number.
int genRandomInt(int minVal, int maxVal);

class SharedMutex
{
private:
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Condition m_LockWriteCond;
Condition m_LockReadCond;

Mutex m_Mutex;
int m_iCountRead;
bool m_bWriterLocked;
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These two fields can be combined into one field. Please see /usr/include/c++/v1/shared_mutex.

Would be also nice that you use exactly the same public API as the standard one so that a prospective drop-in replacement with the standard one from C++17 can be done later.

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I thought about merging those two fields. I however felt that it would hurt readibility for a negligible memory and performance gain.

API has been changed to match the standard one



public:
SharedMutex()
:m_LockWriteCond()
,m_LockReadCond()
,m_Mutex()
,m_iCountRead(0)
,m_bWriterLocked(false)
{
m_iCountRead = 0;
m_bWriterLocked = false;

setupCond(m_LockReadCond, "SharedMutex::m_pLockReadCond");
setupCond(m_LockWriteCond, "SharedMutex::m_pLockWriteCond");
setupMutex(m_Mutex, "SharedMutex::m_pMutex");

}
~SharedMutex()
{
releaseMutex(m_Mutex);
releaseCond(m_LockWriteCond);
releaseCond(m_LockReadCond);
}

void lockWrite()
{
UniqueLock l1(m_Mutex);
if(m_bWriterLocked)
m_LockWriteCond.wait(l1);
m_bWriterLocked = true;
if(m_iCountRead)
m_LockReadCond.wait(l1);


}

void unlockWrite()
{
UniqueLock l2(m_Mutex);
m_bWriterLocked = false;
l2.unlock();
m_LockWriteCond.notify_all();

}

void lockRead()
{
UniqueLock l3(m_Mutex);
if(m_bWriterLocked)
m_LockWriteCond.wait(l3);
m_iCountRead++;
}

void unlockRead()
{
ScopedLock l4(m_Mutex);
m_iCountRead--;
if(m_bWriterLocked && m_iCountRead == 0)
m_LockReadCond.notify_one();
else if (m_iCountRead > 0)
m_LockWriteCond.notify_one();
}

};

} // namespace sync
} // namespace srt

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