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Optimize locking in ComputerManager to reduce reader contention

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This commit is contained in:
Cameron Gutman 2022-10-24 23:55:10 -05:00
parent b7a340bd00
commit cb04925c6e
1 changed files with 20 additions and 7 deletions
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27
app/backend/computermanager.cpp
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@ -442,7 +442,7 @@ void ComputerManager::clientSideAttributeUpdated(NvComputer* computer)
void ComputerManager::handleAboutToQuit() void ComputerManager::handleAboutToQuit()
{ {
QWriteLocker lock(&m_Lock); QReadLocker lock(&m_Lock);
// Interrupt polling threads immediately, so they // Interrupt polling threads immediately, so they
// avoid making additional requests while quitting // avoid making additional requests while quitting
@ -775,16 +775,31 @@ private:
hostAddress.isInSubnet(QHostAddress("192.168.0.0"), 16); hostAddress.isInSubnet(QHostAddress("192.168.0.0"), 16);
{ {
// Check if this PC already exists // Check if this PC already exists using opportunistic read lock
QWriteLocker lock(&m_ComputerManager->m_Lock); m_ComputerManager->m_Lock.lockForRead();
NvComputer* existingComputer = m_ComputerManager->m_KnownHosts.value(newComputer->uuid); NvComputer* existingComputer = m_ComputerManager->m_KnownHosts.value(newComputer->uuid);
// If it doesn't already exist, convert to a write lock in preparation for updating.
//
// NB: ComputerManager's lock protects the host map itself, not the elements inside.
// Those are protected by their individual locks. Since we only mutate the map itself
// when the PC doesn't exist, we need the lock in write-mode for that case only.
if (existingComputer == nullptr) {
m_ComputerManager->m_Lock.unlock();
m_ComputerManager->m_Lock.lockForWrite();
// Since we had to unlock to lock for write, someone could have raced and added
// this PC before us. We have to check again whether it already exists.
existingComputer = m_ComputerManager->m_KnownHosts.value(newComputer->uuid);
}
if (existingComputer != nullptr) { if (existingComputer != nullptr) {
// Fold it into the existing PC // Fold it into the existing PC
bool changed = existingComputer->update(*newComputer); bool changed = existingComputer->update(*newComputer);
delete newComputer; delete newComputer;
// Drop the lock before notifying // Drop the lock before notifying
lock.unlock(); m_ComputerManager->m_Lock.unlock();
// For non-mDNS clients, let them know it succeeded // For non-mDNS clients, let them know it succeeded
if (!m_Mdns) { if (!m_Mdns) {
@ -805,7 +820,7 @@ private:
m_ComputerManager->startPollingComputer(newComputer); m_ComputerManager->startPollingComputer(newComputer);
// Drop the lock before notifying // Drop the lock before notifying
lock.unlock(); m_ComputerManager->m_Lock.unlock();
// If this wasn't added via mDNS but it is a RFC 1918 IPv4 address and not a VPN, // If this wasn't added via mDNS but it is a RFC 1918 IPv4 address and not a VPN,
// go ahead and do the STUN request now to populate an external address. // go ahead and do the STUN request now to populate an external address.
@ -813,9 +828,7 @@ private:
quint32 addr; quint32 addr;
int err = LiFindExternalAddressIP4("stun.moonlight-stream.org", 3478, &addr); int err = LiFindExternalAddressIP4("stun.moonlight-stream.org", 3478, &addr);
if (err == 0) { if (err == 0) {
lock.relock();
newComputer->setRemoteAddress(QHostAddress(qFromBigEndian(addr))); newComputer->setRemoteAddress(QHostAddress(qFromBigEndian(addr)));
lock.unlock();
} }
else { else {
qWarning() << "STUN failed to get WAN address:" << err; qWarning() << "STUN failed to get WAN address:" << err;