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|
/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kDefault
#include "mongo/platform/basic.h"
#include "mongo/db/concurrency/lock_state.h"
#include <vector>
#include "mongo/db/concurrency/flow_control_ticketholder.h"
#include "mongo/db/namespace_string.h"
#include "mongo/db/service_context.h"
#include "mongo/db/storage/flow_control.h"
#include "mongo/logv2/log.h"
#include "mongo/platform/compiler.h"
#include "mongo/stdx/new.h"
#include "mongo/util/background.h"
#include "mongo/util/concurrency/ticketholder.h"
#include "mongo/util/debug_util.h"
#include "mongo/util/fail_point.h"
#include "mongo/util/log.h"
#include "mongo/util/scopeguard.h"
#include "mongo/util/str.h"
namespace mongo {
MONGO_FAIL_POINT_DEFINE(failNonIntentLocksIfWaitNeeded);
MONGO_FAIL_POINT_DEFINE(enableTestOnlyFlagforRSTL);
namespace {
/**
* Tracks global (across all clients) lock acquisition statistics, partitioned into multiple
* buckets to minimize concurrent access conflicts.
*
* Each client has a LockerId that monotonically increases across all client instances. The
* LockerId % 8 is used to index into one of 8 LockStats instances. These LockStats objects must be
* atomically accessed, so maintaining 8 that are indexed by LockerId reduces client conflicts and
* improves concurrent write access. A reader, to collect global lock statics for reporting, will
* sum the results of all 8 disjoint 'buckets' of stats.
*/
class PartitionedInstanceWideLockStats {
PartitionedInstanceWideLockStats(const PartitionedInstanceWideLockStats&) = delete;
PartitionedInstanceWideLockStats& operator=(const PartitionedInstanceWideLockStats&) = delete;
public:
PartitionedInstanceWideLockStats() {}
void recordAcquisition(LockerId id, ResourceId resId, LockMode mode) {
_get(id).recordAcquisition(resId, mode);
}
void recordWait(LockerId id, ResourceId resId, LockMode mode) {
_get(id).recordWait(resId, mode);
}
void recordWaitTime(LockerId id, ResourceId resId, LockMode mode, uint64_t waitMicros) {
_get(id).recordWaitTime(resId, mode, waitMicros);
}
void report(SingleThreadedLockStats* outStats) const {
for (int i = 0; i < NumPartitions; i++) {
outStats->append(_partitions[i].stats);
}
}
void reset() {
for (int i = 0; i < NumPartitions; i++) {
_partitions[i].stats.reset();
}
}
private:
// This alignment is a best effort approach to ensure that each partition falls on a
// separate page/cache line in order to avoid false sharing.
struct alignas(stdx::hardware_destructive_interference_size) AlignedLockStats {
AtomicLockStats stats;
};
enum { NumPartitions = 8 };
AtomicLockStats& _get(LockerId id) {
return _partitions[id % NumPartitions].stats;
}
AlignedLockStats _partitions[NumPartitions];
};
// Global lock manager instance.
LockManager globalLockManager;
// How often (in millis) to check for deadlock if a lock has not been granted for some time
const Milliseconds MaxWaitTime = Milliseconds(500);
// Dispenses unique LockerId identifiers
AtomicWord<unsigned long long> idCounter(0);
// Tracks lock statistics across all Locker instances. Distributes stats across multiple buckets
// indexed by LockerId in order to minimize concurrent access conflicts.
PartitionedInstanceWideLockStats globalStats;
} // namespace
bool LockerImpl::_shouldDelayUnlock(ResourceId resId, LockMode mode) const {
switch (resId.getType()) {
case RESOURCE_MUTEX:
return false;
case RESOURCE_GLOBAL:
case RESOURCE_PBWM:
case RESOURCE_RSTL:
case RESOURCE_DATABASE:
case RESOURCE_COLLECTION:
case RESOURCE_METADATA:
break;
default:
MONGO_UNREACHABLE;
}
switch (mode) {
case MODE_X:
case MODE_IX:
return true;
case MODE_IS:
case MODE_S:
return _sharedLocksShouldTwoPhaseLock;
default:
MONGO_UNREACHABLE;
}
}
bool LockerImpl::isW() const {
return getLockMode(resourceIdGlobal) == MODE_X;
}
bool LockerImpl::isR() const {
return getLockMode(resourceIdGlobal) == MODE_S;
}
bool LockerImpl::isLocked() const {
return getLockMode(resourceIdGlobal) != MODE_NONE;
}
bool LockerImpl::isWriteLocked() const {
return isLockHeldForMode(resourceIdGlobal, MODE_IX);
}
bool LockerImpl::isReadLocked() const {
return isLockHeldForMode(resourceIdGlobal, MODE_IS);
}
bool LockerImpl::isRSTLExclusive() const {
return getLockMode(resourceIdReplicationStateTransitionLock) == MODE_X;
}
bool LockerImpl::isRSTLLocked() const {
return getLockMode(resourceIdReplicationStateTransitionLock) != MODE_NONE;
}
void LockerImpl::dump() const {
StringBuilder ss;
ss << "Locker id " << _id << " status: ";
_lock.lock();
LockRequestsMap::ConstIterator it = _requests.begin();
while (!it.finished()) {
ss << it.key().toString() << " " << lockRequestStatusName(it->status) << " in "
<< modeName(it->mode) << "; ";
it.next();
}
_lock.unlock();
LOGV2(20523, "{ss_str}", "ss_str"_attr = ss.str());
}
//
// CondVarLockGrantNotification
//
CondVarLockGrantNotification::CondVarLockGrantNotification() {
clear();
}
void CondVarLockGrantNotification::clear() {
_result = LOCK_INVALID;
}
LockResult CondVarLockGrantNotification::wait(Milliseconds timeout) {
stdx::unique_lock<Latch> lock(_mutex);
return _cond.wait_for(
lock, timeout.toSystemDuration(), [this] { return _result != LOCK_INVALID; })
? _result
: LOCK_TIMEOUT;
}
LockResult CondVarLockGrantNotification::wait(OperationContext* opCtx, Milliseconds timeout) {
invariant(opCtx);
stdx::unique_lock<Latch> lock(_mutex);
if (opCtx->waitForConditionOrInterruptFor(
_cond, lock, timeout, [this] { return _result != LOCK_INVALID; })) {
// Because waitForConditionOrInterruptFor evaluates the predicate before checking for
// interrupt, it is possible that a killed operation can acquire a lock if the request is
// granted quickly. For that reason, it is necessary to check if the operation has been
// killed at least once before accepting the lock grant.
opCtx->checkForInterrupt();
return _result;
}
return LOCK_TIMEOUT;
}
void CondVarLockGrantNotification::notify(ResourceId resId, LockResult result) {
stdx::unique_lock<Latch> lock(_mutex);
invariant(_result == LOCK_INVALID);
_result = result;
_cond.notify_all();
}
namespace {
TicketHolder* ticketHolders[LockModesCount] = {};
} // namespace
//
// Locker
//
/* static */
void Locker::setGlobalThrottling(class TicketHolder* reading, class TicketHolder* writing) {
ticketHolders[MODE_S] = reading;
ticketHolders[MODE_IS] = reading;
ticketHolders[MODE_IX] = writing;
}
LockerImpl::LockerImpl()
: _id(idCounter.addAndFetch(1)), _wuowNestingLevel(0), _threadId(stdx::this_thread::get_id()) {}
stdx::thread::id LockerImpl::getThreadId() const {
return _threadId;
}
void LockerImpl::updateThreadIdToCurrentThread() {
_threadId = stdx::this_thread::get_id();
}
void LockerImpl::unsetThreadId() {
_threadId = stdx::thread::id(); // Reset to represent a non-executing thread.
}
LockerImpl::~LockerImpl() {
// Cannot delete the Locker while there are still outstanding requests, because the
// LockManager may attempt to access deleted memory. Besides it is probably incorrect
// to delete with unaccounted locks anyways.
invariant(!inAWriteUnitOfWork());
invariant(_numResourcesToUnlockAtEndUnitOfWork == 0);
invariant(_requests.empty());
invariant(_modeForTicket == MODE_NONE);
// Reset the locking statistics so the object can be reused
_stats.reset();
}
Locker::ClientState LockerImpl::getClientState() const {
auto state = _clientState.load();
if (state == kActiveReader && hasLockPending())
state = kQueuedReader;
if (state == kActiveWriter && hasLockPending())
state = kQueuedWriter;
return state;
}
void LockerImpl::reacquireTicket(OperationContext* opCtx) {
invariant(_modeForTicket != MODE_NONE);
auto clientState = _clientState.load();
const bool reader = isSharedLockMode(_modeForTicket);
// Ensure that either we don't have a ticket, or the current ticket mode matches the lock mode.
invariant(clientState == kInactive || (clientState == kActiveReader && reader) ||
(clientState == kActiveWriter && !reader));
// If we already have a ticket, there's nothing to do.
if (clientState != kInactive)
return;
if (!_maxLockTimeout || _uninterruptibleLocksRequested) {
invariant(_acquireTicket(opCtx, _modeForTicket, Date_t::max()));
} else {
uassert(ErrorCodes::LockTimeout,
str::stream() << "Unable to acquire ticket with mode '" << _modeForTicket
<< "' within a max lock request timeout of '" << *_maxLockTimeout
<< "' milliseconds.",
_acquireTicket(opCtx, _modeForTicket, Date_t::now() + *_maxLockTimeout));
}
}
bool LockerImpl::_acquireTicket(OperationContext* opCtx, LockMode mode, Date_t deadline) {
const bool reader = isSharedLockMode(mode);
auto holder = shouldAcquireTicket() ? ticketHolders[mode] : nullptr;
if (holder) {
_clientState.store(reader ? kQueuedReader : kQueuedWriter);
// If the ticket wait is interrupted, restore the state of the client.
auto restoreStateOnErrorGuard = makeGuard([&] { _clientState.store(kInactive); });
OperationContext* interruptible = _uninterruptibleLocksRequested ? nullptr : opCtx;
if (deadline == Date_t::max()) {
holder->waitForTicket(interruptible);
} else if (!holder->waitForTicketUntil(interruptible, deadline)) {
return false;
}
restoreStateOnErrorGuard.dismiss();
}
_clientState.store(reader ? kActiveReader : kActiveWriter);
return true;
}
void LockerImpl::lockGlobal(OperationContext* opCtx, LockMode mode, Date_t deadline) {
dassert(isLocked() == (_modeForTicket != MODE_NONE));
if (_modeForTicket == MODE_NONE) {
if (_uninterruptibleLocksRequested) {
// Ignore deadline and _maxLockTimeout.
invariant(_acquireTicket(opCtx, mode, Date_t::max()));
} else {
auto beforeAcquire = Date_t::now();
deadline = std::min(deadline,
_maxLockTimeout ? beforeAcquire + *_maxLockTimeout : Date_t::max());
uassert(ErrorCodes::LockTimeout,
str::stream() << "Unable to acquire ticket with mode '" << _modeForTicket
<< "' within a max lock request timeout of '"
<< Date_t::now() - beforeAcquire << "' milliseconds.",
_acquireTicket(opCtx, mode, deadline));
}
_modeForTicket = mode;
}
LockMode actualLockMode = mode;
if (opCtx) {
auto storageEngine = opCtx->getServiceContext()->getStorageEngine();
if (storageEngine && !storageEngine->supportsDBLocking()) {
actualLockMode = isSharedLockMode(mode) ? MODE_S : MODE_X;
}
}
const LockResult result = _lockBegin(opCtx, resourceIdGlobal, actualLockMode);
// Fast, uncontended path
if (result == LOCK_OK)
return;
invariant(result == LOCK_WAITING);
_lockComplete(opCtx, resourceIdGlobal, actualLockMode, deadline);
}
bool LockerImpl::unlockGlobal() {
if (!unlock(resourceIdGlobal)) {
return false;
}
invariant(!inAWriteUnitOfWork());
LockRequestsMap::Iterator it = _requests.begin();
while (!it.finished()) {
// If we're here we should only have one reference to any lock. It is a programming
// error for any lock used with multi-granularity locking to have more references than
// the global lock, because every scope starts by calling lockGlobal.
const auto resType = it.key().getType();
if (resType == RESOURCE_GLOBAL || resType == RESOURCE_PBWM || resType == RESOURCE_RSTL ||
resType == RESOURCE_MUTEX) {
it.next();
} else {
invariant(_unlockImpl(&it));
}
}
return true;
}
void LockerImpl::beginWriteUnitOfWork() {
_wuowNestingLevel++;
}
void LockerImpl::endWriteUnitOfWork() {
invariant(_wuowNestingLevel > 0);
if (--_wuowNestingLevel > 0) {
// Don't do anything unless leaving outermost WUOW.
return;
}
LockRequestsMap::Iterator it = _requests.begin();
while (_numResourcesToUnlockAtEndUnitOfWork > 0) {
if (it->unlockPending) {
invariant(!it.finished());
_numResourcesToUnlockAtEndUnitOfWork--;
}
while (it->unlockPending > 0) {
// If a lock is converted, unlock() may be called multiple times on a resource within
// the same WriteUnitOfWork. All such unlock() requests must thus be fulfilled here.
it->unlockPending--;
unlock(it.key());
}
it.next();
}
}
void LockerImpl::releaseWriteUnitOfWork(WUOWLockSnapshot* stateOut) {
stateOut->wuowNestingLevel = _wuowNestingLevel;
_wuowNestingLevel = 0;
for (auto it = _requests.begin(); _numResourcesToUnlockAtEndUnitOfWork > 0; it.next()) {
if (it->unlockPending) {
while (it->unlockPending) {
it->unlockPending--;
stateOut->unlockPendingLocks.push_back({it.key(), it->mode});
}
_numResourcesToUnlockAtEndUnitOfWork--;
}
}
}
void LockerImpl::restoreWriteUnitOfWork(const WUOWLockSnapshot& stateToRestore) {
invariant(_numResourcesToUnlockAtEndUnitOfWork == 0);
invariant(!inAWriteUnitOfWork());
for (auto& lock : stateToRestore.unlockPendingLocks) {
auto it = _requests.begin();
while (it && !(it.key() == lock.resourceId && it->mode == lock.mode)) {
it.next();
}
invariant(!it.finished());
if (!it->unlockPending) {
_numResourcesToUnlockAtEndUnitOfWork++;
}
it->unlockPending++;
}
// Equivalent to call beginWriteUnitOfWork() multiple times.
_wuowNestingLevel = stateToRestore.wuowNestingLevel;
}
bool LockerImpl::releaseWriteUnitOfWorkAndUnlock(LockSnapshot* stateOut) {
// Only the global WUOW can be released, since we never need to release and restore
// nested WUOW's. Thus we don't have to remember the nesting level.
invariant(_wuowNestingLevel == 1);
--_wuowNestingLevel;
invariant(!isGlobalLockedRecursively());
// All locks should be pending to unlock.
invariant(_requests.size() == _numResourcesToUnlockAtEndUnitOfWork);
for (auto it = _requests.begin(); it; it.next()) {
// No converted lock so we don't need to unlock more than once.
invariant(it->unlockPending == 1);
it->unlockPending--;
}
_numResourcesToUnlockAtEndUnitOfWork = 0;
return saveLockStateAndUnlock(stateOut);
}
void LockerImpl::restoreWriteUnitOfWorkAndLock(OperationContext* opCtx,
const LockSnapshot& stateToRestore) {
if (stateToRestore.globalMode != MODE_NONE) {
restoreLockState(opCtx, stateToRestore);
}
invariant(_numResourcesToUnlockAtEndUnitOfWork == 0);
for (auto it = _requests.begin(); it; it.next()) {
invariant(_shouldDelayUnlock(it.key(), (it->mode)));
invariant(it->unlockPending == 0);
it->unlockPending++;
}
_numResourcesToUnlockAtEndUnitOfWork = static_cast<unsigned>(_requests.size());
beginWriteUnitOfWork();
}
void LockerImpl::lock(OperationContext* opCtx, ResourceId resId, LockMode mode, Date_t deadline) {
// `lockGlobal` must be called to lock `resourceIdGlobal`.
invariant(resId != resourceIdGlobal);
const LockResult result = _lockBegin(opCtx, resId, mode);
// Fast, uncontended path
if (result == LOCK_OK)
return;
invariant(result == LOCK_WAITING);
_lockComplete(opCtx, resId, mode, deadline);
}
void LockerImpl::downgrade(ResourceId resId, LockMode newMode) {
LockRequestsMap::Iterator it = _requests.find(resId);
globalLockManager.downgrade(it.objAddr(), newMode);
}
bool LockerImpl::unlock(ResourceId resId) {
LockRequestsMap::Iterator it = _requests.find(resId);
// Don't attempt to unlock twice. This can happen when an interrupted global lock is destructed.
if (it.finished())
return false;
if (inAWriteUnitOfWork() && _shouldDelayUnlock(it.key(), (it->mode))) {
// Only delay unlocking if the lock is not acquired more than once. Otherwise, we can simply
// call _unlockImpl to decrement recursiveCount instead of incrementing unlockPending. This
// is safe because the lock is still being held in the strongest mode necessary.
if (it->recursiveCount > 1) {
// Invariant that the lock is still being held.
invariant(!_unlockImpl(&it));
return false;
}
if (!it->unlockPending) {
_numResourcesToUnlockAtEndUnitOfWork++;
}
it->unlockPending++;
// unlockPending will be incremented if a lock is converted or acquired in the same mode
// recursively, and unlock() is called multiple times on one ResourceId.
invariant(it->unlockPending <= it->recursiveCount);
return false;
}
return _unlockImpl(&it);
}
bool LockerImpl::unlockRSTLforPrepare() {
auto rstlRequest = _requests.find(resourceIdReplicationStateTransitionLock);
// Don't attempt to unlock twice. This can happen when an interrupted global lock is destructed.
if (!rstlRequest)
return false;
// If the RSTL is 'unlockPending' and we are fully unlocking it, then we do not want to
// attempt to unlock the RSTL when the WUOW ends, since it will already be unlocked.
if (rstlRequest->unlockPending) {
rstlRequest->unlockPending = 0;
_numResourcesToUnlockAtEndUnitOfWork--;
}
// Reset the recursiveCount to 1 so that we fully unlock the RSTL. Since it will be fully
// unlocked, any future unlocks will be noops anyways.
rstlRequest->recursiveCount = 1;
return _unlockImpl(&rstlRequest);
}
LockMode LockerImpl::getLockMode(ResourceId resId) const {
scoped_spinlock scopedLock(_lock);
const LockRequestsMap::ConstIterator it = _requests.find(resId);
if (!it)
return MODE_NONE;
return it->mode;
}
bool LockerImpl::isLockHeldForMode(ResourceId resId, LockMode mode) const {
return isModeCovered(mode, getLockMode(resId));
}
bool LockerImpl::isDbLockedForMode(StringData dbName, LockMode mode) const {
invariant(nsIsDbOnly(dbName));
if (isW())
return true;
if (isR() && isSharedLockMode(mode))
return true;
const ResourceId resIdDb(RESOURCE_DATABASE, dbName);
return isLockHeldForMode(resIdDb, mode);
}
bool LockerImpl::isCollectionLockedForMode(const NamespaceString& nss, LockMode mode) const {
invariant(nss.coll().size());
if (isW())
return true;
if (isR() && isSharedLockMode(mode))
return true;
const ResourceId resIdDb(RESOURCE_DATABASE, nss.db());
LockMode dbMode = getLockMode(resIdDb);
if (!shouldConflictWithSecondaryBatchApplication())
return true;
switch (dbMode) {
case MODE_NONE:
return false;
case MODE_X:
return true;
case MODE_S:
return isSharedLockMode(mode);
case MODE_IX:
case MODE_IS: {
const ResourceId resIdColl(RESOURCE_COLLECTION, nss.ns());
return isLockHeldForMode(resIdColl, mode);
} break;
case LockModesCount:
break;
}
MONGO_UNREACHABLE;
return false;
}
bool LockerImpl::wasGlobalLockTakenForWrite() const {
return _globalLockMode & ((1 << MODE_IX) | (1 << MODE_X));
}
bool LockerImpl::wasGlobalLockTakenInModeConflictingWithWrites() const {
return _wasGlobalLockTakenInModeConflictingWithWrites.load();
}
bool LockerImpl::wasGlobalLockTaken() const {
return _globalLockMode != (1 << MODE_NONE);
}
void LockerImpl::setGlobalLockTakenInMode(LockMode mode) {
_globalLockMode |= (1 << mode);
if (mode == MODE_IX || mode == MODE_X || mode == MODE_S) {
_wasGlobalLockTakenInModeConflictingWithWrites.store(true);
}
}
ResourceId LockerImpl::getWaitingResource() const {
scoped_spinlock scopedLock(_lock);
LockRequestsMap::ConstIterator it = _requests.begin();
while (!it.finished()) {
if (it->status == LockRequest::STATUS_WAITING ||
it->status == LockRequest::STATUS_CONVERTING) {
return it.key();
}
it.next();
}
return ResourceId();
}
void LockerImpl::getLockerInfo(LockerInfo* lockerInfo,
const boost::optional<SingleThreadedLockStats> lockStatsBase) const {
invariant(lockerInfo);
// Zero-out the contents
lockerInfo->locks.clear();
lockerInfo->waitingResource = ResourceId();
lockerInfo->stats.reset();
_lock.lock();
LockRequestsMap::ConstIterator it = _requests.begin();
while (!it.finished()) {
OneLock info;
info.resourceId = it.key();
info.mode = it->mode;
lockerInfo->locks.push_back(info);
it.next();
}
_lock.unlock();
std::sort(lockerInfo->locks.begin(), lockerInfo->locks.end());
lockerInfo->waitingResource = getWaitingResource();
lockerInfo->stats.append(_stats);
// lockStatsBase is a snapshot of lock stats taken when the sub-operation starts. Only
// sub-operations have lockStatsBase.
if (lockStatsBase)
// Adjust the lock stats by subtracting the lockStatsBase. No mutex is needed because
// lockStatsBase is immutable.
lockerInfo->stats.subtract(*lockStatsBase);
}
boost::optional<Locker::LockerInfo> LockerImpl::getLockerInfo(
const boost::optional<SingleThreadedLockStats> lockStatsBase) const {
Locker::LockerInfo lockerInfo;
getLockerInfo(&lockerInfo, lockStatsBase);
return std::move(lockerInfo);
}
bool LockerImpl::saveLockStateAndUnlock(Locker::LockSnapshot* stateOut) {
// We shouldn't be saving and restoring lock state from inside a WriteUnitOfWork.
invariant(!inAWriteUnitOfWork());
// Clear out whatever is in stateOut.
stateOut->locks.clear();
stateOut->globalMode = MODE_NONE;
// First, we look at the global lock. There is special handling for this so we store it
// separately from the more pedestrian locks.
LockRequestsMap::Iterator globalRequest = _requests.find(resourceIdGlobal);
if (!globalRequest) {
// If there's no global lock there isn't really anything to do. Check that.
for (auto it = _requests.begin(); !it.finished(); it.next()) {
invariant(it.key().getType() == RESOURCE_MUTEX);
}
return false;
}
// If the global lock or RSTL has been acquired more than once, we're probably somewhere in a
// DBDirectClient call. It's not safe to release and reacquire locks -- the context using
// the DBDirectClient is probably not prepared for lock release.
LockRequestsMap::Iterator rstlRequest =
_requests.find(resourceIdReplicationStateTransitionLock);
if (globalRequest->recursiveCount > 1 || (rstlRequest && rstlRequest->recursiveCount > 1)) {
return false;
}
// The global lock must have been acquired just once
stateOut->globalMode = globalRequest->mode;
invariant(unlock(resourceIdGlobal));
// Next, the non-global locks.
for (LockRequestsMap::Iterator it = _requests.begin(); !it.finished(); it.next()) {
const ResourceId resId = it.key();
const ResourceType resType = resId.getType();
if (resType == RESOURCE_MUTEX)
continue;
// We should never have to save and restore metadata locks.
invariant(RESOURCE_DATABASE == resType || RESOURCE_COLLECTION == resType ||
(RESOURCE_PBWM == resType && isSharedLockMode(it->mode)) ||
(RESOURCE_RSTL == resType && it->mode == MODE_IX));
// And, stuff the info into the out parameter.
OneLock info;
info.resourceId = resId;
info.mode = it->mode;
stateOut->locks.push_back(info);
invariant(unlock(resId));
}
invariant(!isLocked());
// Sort locks by ResourceId. They'll later be acquired in this canonical locking order.
std::sort(stateOut->locks.begin(), stateOut->locks.end());
return true;
}
void LockerImpl::restoreLockState(OperationContext* opCtx, const Locker::LockSnapshot& state) {
// We shouldn't be restoring lock state from inside a WriteUnitOfWork.
invariant(!inAWriteUnitOfWork());
invariant(_modeForTicket == MODE_NONE);
invariant(_clientState.load() == kInactive);
if (opCtx) {
getFlowControlTicket(opCtx, state.globalMode);
}
std::vector<OneLock>::const_iterator it = state.locks.begin();
// If we locked the PBWM, it must be locked before the resourceIdGlobal and
// resourceIdReplicationStateTransitionLock resources.
if (it != state.locks.end() && it->resourceId == resourceIdParallelBatchWriterMode) {
lock(opCtx, it->resourceId, it->mode);
it++;
}
// If we locked the RSTL, it must be locked before the resourceIdGlobal resource.
if (it != state.locks.end() && it->resourceId == resourceIdReplicationStateTransitionLock) {
lock(opCtx, it->resourceId, it->mode);
it++;
}
lockGlobal(opCtx, state.globalMode);
for (; it != state.locks.end(); it++) {
lock(opCtx, it->resourceId, it->mode);
}
invariant(_modeForTicket != MODE_NONE);
}
LockResult LockerImpl::_lockBegin(OperationContext* opCtx, ResourceId resId, LockMode mode) {
dassert(!getWaitingResource().isValid());
LockRequest* request;
bool isNew = true;
LockRequestsMap::Iterator it = _requests.find(resId);
if (!it) {
scoped_spinlock scopedLock(_lock);
LockRequestsMap::Iterator itNew = _requests.insert(resId);
itNew->initNew(this, &_notify);
request = itNew.objAddr();
} else {
request = it.objAddr();
isNew = false;
}
// If unlockPending is nonzero, that means a LockRequest already exists for this resource but
// is planned to be released at the end of this WUOW due to two-phase locking. Rather than
// unlocking the existing request, we can reuse it if the existing mode matches the new mode.
if (request->unlockPending && isModeCovered(mode, request->mode)) {
request->unlockPending--;
if (!request->unlockPending) {
_numResourcesToUnlockAtEndUnitOfWork--;
}
return LOCK_OK;
}
// Making this call here will record lock re-acquisitions and conversions as well.
globalStats.recordAcquisition(_id, resId, mode);
_stats.recordAcquisition(resId, mode);
// Give priority to the full modes for Global, PBWM, and RSTL resources so we don't stall global
// operations such as shutdown or stepdown.
const ResourceType resType = resId.getType();
if (resType == RESOURCE_GLOBAL || resType == RESOURCE_PBWM || resType == RESOURCE_RSTL) {
if (mode == MODE_S || mode == MODE_X) {
request->enqueueAtFront = true;
request->compatibleFirst = true;
}
} else if (resType != RESOURCE_MUTEX) {
// This is all sanity checks that the global locks are always be acquired
// before any other lock has been acquired and they must be in sync with the nesting.
if (kDebugBuild) {
const LockRequestsMap::Iterator itGlobal = _requests.find(resourceIdGlobal);
invariant(itGlobal->recursiveCount > 0);
invariant(itGlobal->mode != MODE_NONE);
};
}
// The notification object must be cleared before we invoke the lock manager, because
// otherwise we might reset state if the lock becomes granted very fast.
_notify.clear();
LockResult result = isNew ? globalLockManager.lock(resId, request, mode)
: globalLockManager.convert(resId, request, mode);
if (result == LOCK_WAITING) {
globalStats.recordWait(_id, resId, mode);
_stats.recordWait(resId, mode);
} else if (result == LOCK_OK && opCtx && _uninterruptibleLocksRequested == 0) {
// Lock acquisitions are not allowed to succeed when opCtx is marked as interrupted, unless
// the caller requested an uninterruptible lock.
auto interruptStatus = opCtx->checkForInterruptNoAssert();
if (!interruptStatus.isOK()) {
auto unlockIt = _requests.find(resId);
invariant(unlockIt);
_unlockImpl(&unlockIt);
uassertStatusOK(interruptStatus);
}
}
return result;
}
void LockerImpl::_lockComplete(OperationContext* opCtx,
ResourceId resId,
LockMode mode,
Date_t deadline) {
// Clean up the state on any failed lock attempts.
auto unlockOnErrorGuard = makeGuard([&] {
LockRequestsMap::Iterator it = _requests.find(resId);
invariant(it);
_unlockImpl(&it);
});
// This failpoint is used to time out non-intent locks if they cannot be granted immediately
// for user operations. Testing-only.
const bool isUserOperation = opCtx && opCtx->getClient()->isFromUserConnection();
if (!_uninterruptibleLocksRequested && isUserOperation &&
MONGO_unlikely(failNonIntentLocksIfWaitNeeded.shouldFail())) {
uassert(ErrorCodes::LockTimeout,
str::stream() << "Cannot immediately acquire lock '" << resId.toString()
<< "'. Timing out due to failpoint.",
(mode == MODE_IS || mode == MODE_IX));
}
LockResult result;
Milliseconds timeout;
if (deadline == Date_t::max()) {
timeout = Milliseconds::max();
} else if (deadline <= Date_t()) {
timeout = Milliseconds(0);
} else {
timeout = deadline - Date_t::now();
}
timeout = std::min(timeout, _maxLockTimeout ? *_maxLockTimeout : Milliseconds::max());
if (_uninterruptibleLocksRequested) {
timeout = Milliseconds::max();
}
// Don't go sleeping without bound in order to be able to report long waits.
Milliseconds waitTime = std::min(timeout, MaxWaitTime);
const uint64_t startOfTotalWaitTime = curTimeMicros64();
uint64_t startOfCurrentWaitTime = startOfTotalWaitTime;
while (true) {
// It is OK if this call wakes up spuriously, because we re-evaluate the remaining
// wait time anyways.
// If we have an operation context, we want to use its interruptible wait so that
// pending lock acquisitions can be cancelled, so long as no callers have requested an
// uninterruptible lock.
if (opCtx && _uninterruptibleLocksRequested == 0) {
result = _notify.wait(opCtx, waitTime);
} else {
result = _notify.wait(waitTime);
}
// Account for the time spent waiting on the notification object
const uint64_t curTimeMicros = curTimeMicros64();
const uint64_t elapsedTimeMicros = curTimeMicros - startOfCurrentWaitTime;
startOfCurrentWaitTime = curTimeMicros;
globalStats.recordWaitTime(_id, resId, mode, elapsedTimeMicros);
_stats.recordWaitTime(resId, mode, elapsedTimeMicros);
if (result == LOCK_OK)
break;
// If infinite timeout was requested, just keep waiting
if (timeout == Milliseconds::max()) {
continue;
}
const auto totalBlockTime = duration_cast<Milliseconds>(
Microseconds(int64_t(curTimeMicros - startOfTotalWaitTime)));
waitTime = (totalBlockTime < timeout) ? std::min(timeout - totalBlockTime, MaxWaitTime)
: Milliseconds(0);
// Check if the lock acquisition has timed out. If we have an operation context and client
// we can provide additional diagnostics data.
if (waitTime == Milliseconds(0)) {
std::string timeoutMessage = str::stream()
<< "Unable to acquire " << modeName(mode) << " lock on '" << resId.toString()
<< "' within " << timeout << ".";
if (opCtx && opCtx->getClient()) {
timeoutMessage = str::stream()
<< timeoutMessage << " opId: " << opCtx->getOpID()
<< ", op: " << opCtx->getClient()->desc()
<< ", connId: " << opCtx->getClient()->getConnectionId() << ".";
}
uasserted(ErrorCodes::LockTimeout, timeoutMessage);
}
}
invariant(result == LOCK_OK);
unlockOnErrorGuard.dismiss();
}
void LockerImpl::getFlowControlTicket(OperationContext* opCtx, LockMode lockMode) {
auto ticketholder = FlowControlTicketholder::get(opCtx);
if (ticketholder && lockMode == LockMode::MODE_IX && _clientState.load() == kInactive &&
opCtx->shouldParticipateInFlowControl() && !_uninterruptibleLocksRequested) {
// FlowControl only acts when a MODE_IX global lock is being taken. The clientState is only
// being modified here to change serverStatus' `globalLock.currentQueue` metrics. This
// method must not exit with a side-effect on the clientState. That value is also used for
// tracking whether other resources need to be released.
_clientState.store(kQueuedWriter);
auto restoreState = makeGuard([&] { _clientState.store(kInactive); });
ticketholder->getTicket(opCtx, &_flowControlStats);
}
}
LockResult LockerImpl::lockRSTLBegin(OperationContext* opCtx, LockMode mode) {
bool testOnly = false;
if (MONGO_unlikely(enableTestOnlyFlagforRSTL.shouldFail())) {
testOnly = true;
}
invariant(testOnly || mode == MODE_IX || mode == MODE_X);
return _lockBegin(opCtx, resourceIdReplicationStateTransitionLock, mode);
}
void LockerImpl::lockRSTLComplete(OperationContext* opCtx, LockMode mode, Date_t deadline) {
_lockComplete(opCtx, resourceIdReplicationStateTransitionLock, mode, deadline);
}
void LockerImpl::releaseTicket() {
invariant(_modeForTicket != MODE_NONE);
_releaseTicket();
}
void LockerImpl::_releaseTicket() {
auto holder = shouldAcquireTicket() ? ticketHolders[_modeForTicket] : nullptr;
if (holder) {
holder->release();
}
_clientState.store(kInactive);
}
bool LockerImpl::_unlockImpl(LockRequestsMap::Iterator* it) {
if (globalLockManager.unlock(it->objAddr())) {
if (it->key() == resourceIdGlobal) {
invariant(_modeForTicket != MODE_NONE);
// We may have already released our ticket through a call to releaseTicket().
if (_clientState.load() != kInactive) {
_releaseTicket();
}
_modeForTicket = MODE_NONE;
}
scoped_spinlock scopedLock(_lock);
it->remove();
return true;
}
return false;
}
bool LockerImpl::isGlobalLockedRecursively() {
auto globalLockRequest = _requests.find(resourceIdGlobal);
return !globalLockRequest.finished() && globalLockRequest->recursiveCount > 1;
}
//
// Auto classes
//
namespace {
/**
* Periodically purges unused lock buckets. The first time the lock is used again after
* cleanup it needs to be allocated, and similarly, every first use by a client for an intent
* mode may need to create a partitioned lock head. Cleanup is done roughly once a minute.
*/
class UnusedLockCleaner : PeriodicTask {
public:
std::string taskName() const {
return "UnusedLockCleaner";
}
void taskDoWork() {
LOGV2_DEBUG(20524, 2, "cleaning up unused lock buckets of the global lock manager");
getGlobalLockManager()->cleanupUnusedLocks();
}
} unusedLockCleaner;
} // namespace
//
// Standalone functions
//
LockManager* getGlobalLockManager() {
return &globalLockManager;
}
void reportGlobalLockingStats(SingleThreadedLockStats* outStats) {
globalStats.report(outStats);
}
void resetGlobalLockStats() {
globalStats.reset();
}
// Hardcoded resource IDs.
const ResourceId resourceIdLocalDB = ResourceId(RESOURCE_DATABASE, StringData("local"));
const ResourceId resourceIdOplog = ResourceId(RESOURCE_COLLECTION, StringData("local.oplog.rs"));
const ResourceId resourceIdAdminDB = ResourceId(RESOURCE_DATABASE, StringData("admin"));
const ResourceId resourceIdGlobal = ResourceId(RESOURCE_GLOBAL, 1ULL);
const ResourceId resourceIdParallelBatchWriterMode = ResourceId(RESOURCE_PBWM, 1ULL);
const ResourceId resourceIdReplicationStateTransitionLock = ResourceId(RESOURCE_RSTL, 1ULL);
} // namespace mongo
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