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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_LOGV2_DEFAULT_COMPONENT ::mongo::logv2::LogComponent::kDefault
#include "mongo/platform/basic.h"
#include "mongo/db/concurrency/lock_manager.h"
#include <fmt/format.h>
#include <fmt/ostream.h>
#include "mongo/base/data_type_endian.h"
#include "mongo/base/data_view.h"
#include "mongo/base/static_assert.h"
#include "mongo/bson/bsonobjbuilder.h"
#include "mongo/config.h"
#include "mongo/db/catalog/collection_catalog.h"
#include "mongo/db/concurrency/d_concurrency.h"
#include "mongo/db/concurrency/locker.h"
#include "mongo/logv2/log.h"
#include "mongo/util/assert_util.h"
#include "mongo/util/str.h"
#include "mongo/util/timer.h"
namespace mongo {
namespace {
template <typename T>
std::string formatHex(T&& x) {
return format(FMT_STRING("{:#x}"), x);
}
std::string formatPtr(const void* x) {
return formatHex(reinterpret_cast<uintptr_t>(x));
}
std::string formatThreadId(stdx::thread::id x) {
return format(FMT_STRING("{}"), x);
}
/**
* Map of conflicts. 'LockConflictsTable[newMode] & existingMode != 0' means that a new request
* with the given 'newMode' conflicts with an existing request with mode 'existingMode'.
*/
static const int LockConflictsTable[] = {
// MODE_NONE
0,
// MODE_IS
(1 << MODE_X),
// MODE_IX
(1 << MODE_S) | (1 << MODE_X),
// MODE_S
(1 << MODE_IX) | (1 << MODE_X),
// MODE_X
(1 << MODE_S) | (1 << MODE_X) | (1 << MODE_IS) | (1 << MODE_IX),
};
// Mask of modes
const uint64_t intentModes = (1 << MODE_IS) | (1 << MODE_IX);
// Ensure we do not add new modes without updating the conflicts table
MONGO_STATIC_ASSERT((sizeof(LockConflictsTable) / sizeof(LockConflictsTable[0])) == LockModesCount);
/**
* Maps the mode id to a string.
*/
static const char* LockModeNames[] = {"NONE", "IS", "IX", "S", "X"};
static const char* LegacyLockModeNames[] = {"", "r", "w", "R", "W"};
// Ensure we do not add new modes without updating the names array
MONGO_STATIC_ASSERT((sizeof(LockModeNames) / sizeof(LockModeNames[0])) == LockModesCount);
MONGO_STATIC_ASSERT((sizeof(LegacyLockModeNames) / sizeof(LegacyLockModeNames[0])) ==
LockModesCount);
// Helper functions for the lock modes
bool conflicts(LockMode newMode, uint32_t existingModesMask) {
return (LockConflictsTable[newMode] & existingModesMask) != 0;
}
uint32_t modeMask(LockMode mode) {
return 1 << mode;
}
/**
* Maps the LockRequest status to a human-readable string.
*/
static const char* LockRequestStatusNames[] = {
"new",
"granted",
"waiting",
"converting",
};
// Ensure we do not add new status types without updating the names array
MONGO_STATIC_ASSERT((sizeof(LockRequestStatusNames) / sizeof(LockRequestStatusNames[0])) ==
LockRequest::StatusCount);
} // namespace
/**
* There is one of these objects for each resource that has a lock request. Empty objects (i.e.
* LockHead with no requests) are allowed to exist on the lock manager's hash table.
*
* The memory and lifetime is controlled entirely by the LockManager class.
*
* Not thread-safe and should only be accessed under the LockManager's bucket lock. Must be locked
* before locking a partition, not after.
*/
struct LockHead {
/**
* Used for initialization of a LockHead, which might have been retrieved from cache and also in
* order to keep the LockHead structure a POD.
*/
void initNew(ResourceId resId) {
resourceId = resId;
grantedList.reset();
memset(grantedCounts, 0, sizeof(grantedCounts));
grantedModes = 0;
conflictList.reset();
memset(conflictCounts, 0, sizeof(conflictCounts));
conflictModes = 0;
conversionsCount = 0;
compatibleFirstCount = 0;
}
/**
* True iff there may be partitions with granted requests for this resource.
*/
bool partitioned() const {
return !partitions.empty();
}
/**
* Locates the request corresponding to the particular locker or returns nullptr. Must be called
* with the bucket holding this lock head locked.
*/
LockRequest* findRequest(LockerId lockerId) const {
// Check the granted queue first
for (LockRequest* it = grantedList._front; it != nullptr; it = it->next) {
if (it->locker->getId() == lockerId) {
return it;
}
}
// Check the conflict queue second
for (LockRequest* it = conflictList._front; it != nullptr; it = it->next) {
if (it->locker->getId() == lockerId) {
return it;
}
}
return nullptr;
}
/**
* Finish creation of request and put it on the LockHead's conflict or granted queues. Returns
* LOCK_WAITING for conflict case and LOCK_OK otherwise.
*/
LockResult newRequest(LockRequest* request) {
invariant(!request->partitionedLock);
request->lock = this;
// We cannot set request->partitioned to false, as this might be a migration, in which case
// access to that field is not protected. The 'partitioned' member instead indicates if a
// request was initially partitioned.
// New lock request. Queue after all granted modes and after any already requested
// conflicting modes
if (conflicts(request->mode, grantedModes) ||
(!compatibleFirstCount && conflicts(request->mode, conflictModes))) {
request->status = LockRequest::STATUS_WAITING;
// Put it on the conflict queue. Conflicts are granted front to back.
if (request->enqueueAtFront) {
conflictList.push_front(request);
} else {
conflictList.push_back(request);
}
incConflictModeCount(request->mode);
return LOCK_WAITING;
}
// No conflict, new request
request->status = LockRequest::STATUS_GRANTED;
grantedList.push_back(request);
incGrantedModeCount(request->mode);
if (request->compatibleFirst) {
compatibleFirstCount++;
}
return LOCK_OK;
}
/**
* Lock each partitioned LockHead in turn, and move any (granted) intent mode requests for
* lock->resourceId to lock, which must itself already be locked.
*/
void migratePartitionedLockHeads();
// Methods to maintain the granted queue
void incGrantedModeCount(LockMode mode) {
invariant(grantedCounts[mode] >= 0);
if (++grantedCounts[mode] == 1) {
invariant((grantedModes & modeMask(mode)) == 0);
grantedModes |= modeMask(mode);
}
}
void decGrantedModeCount(LockMode mode) {
invariant(grantedCounts[mode] >= 1);
if (--grantedCounts[mode] == 0) {
invariant((grantedModes & modeMask(mode)) == modeMask(mode));
grantedModes &= ~modeMask(mode);
}
}
// Methods to maintain the conflict queue
void incConflictModeCount(LockMode mode) {
invariant(conflictCounts[mode] >= 0);
if (++conflictCounts[mode] == 1) {
invariant((conflictModes & modeMask(mode)) == 0);
conflictModes |= modeMask(mode);
}
}
void decConflictModeCount(LockMode mode) {
invariant(conflictCounts[mode] >= 1);
if (--conflictCounts[mode] == 0) {
invariant((conflictModes & modeMask(mode)) == modeMask(mode));
conflictModes &= ~modeMask(mode);
}
}
// Id of the resource which is protected by this lock. Initialized at construction time and does
// not change.
ResourceId resourceId;
//
// Granted queue
//
// Doubly-linked list of requests, which have been granted. Newly granted requests go to
// the end of the queue. Conversion requests are granted from the beginning forward.
LockRequestList grantedList;
// Counts the grants and conversion counts for each of the supported lock modes. These
// counts should exactly match the aggregated modes on the granted list.
uint32_t grantedCounts[LockModesCount];
// Bit-mask of the granted + converting modes on the granted queue. Maintained in lock-step
// with the grantedCounts array.
uint32_t grantedModes;
//
// Conflict queue
//
// Doubly-linked list of requests, which have not been granted yet because they conflict
// with the set of granted modes. Requests are queued at the end of the queue and are
// granted from the beginning forward, which gives these locks FIFO ordering. Exceptions to the
// FIFO rule are strong lock requests for global resources, such as MODE_X for Global.
LockRequestList conflictList;
// Counts the conflicting requests for each of the lock modes. These counts should exactly
// match the aggregated modes on the conflicts list.
uint32_t conflictCounts[LockModesCount];
// Bit-mask of the conflict modes on the conflict queue. Maintained in lock-step with the
// conflictCounts array.
uint32_t conflictModes;
// References partitions that may have PartitionedLockHeads for this LockHead.
// Non-empty implies the lock has no conflicts and only has intent modes as grantedModes.
// TODO: Remove this vector and make LockHead a POD
std::vector<LockManager::Partition*> partitions;
//
// Conversion
//
// Counts the number of requests on the granted queue, which have requested any kind of
// conflicting conversion and are blocked (i.e. all requests which are currently
// STATUS_CONVERTING). This is an optimization for unlocking in that we do not need to
// check the granted queue for requests in STATUS_CONVERTING if this count is zero. This
// saves cycles in the regular case and only burdens the less-frequent lock upgrade case.
uint32_t conversionsCount;
// Counts the number of requests on the granted queue, which have requested that the policy
// be switched to compatible-first. As long as this value is > 0, the policy will stay
// compatible-first.
uint32_t compatibleFirstCount;
};
/**
* The PartitionedLockHead allows optimizing the case where requests overwhelmingly use
* the intent lock modes MODE_IS and MODE_IX, which are compatible with each other.
* Having to use a single LockHead causes contention where none would be needed.
* So, each Locker is associated with a specific partition containing a mapping
* of resourceId to PartitionedLockHead.
*
* As long as all lock requests for a resource have an intent mode, as opposed to a conflicting
* mode, its LockHead may reference PartitionedLockHeads. A partitioned LockHead will not have
* any conflicts. The total set of granted requests (with intent mode) is the union of
* its grantedList and all grantedLists in PartitionedLockHeads.
*
* The existence of a PartitionedLockHead for a resource implies that its LockHead is
* partitioned. If a conflicting request is made on a LockHead, all requests from
* PartitionedLockHeads are migrated to that LockHead and the LockHead no longer partitioned.
*
* Not thread-safe, must be accessed under its partition lock.
* May not lock a LockManager bucket while holding a partition lock.
*/
struct PartitionedLockHead {
void initNew(ResourceId resId) {
grantedList.reset();
}
void newRequest(LockRequest* request) {
invariant(request->partitioned);
invariant(!request->lock);
request->partitionedLock = this;
request->status = LockRequest::STATUS_GRANTED;
grantedList.push_back(request);
}
// Doubly-linked list of requests, which have been granted. Newly granted requests go to the end
// of the queue. The PartitionedLockHead never contains anything but granted requests with
// intent modes.
LockRequestList grantedList;
};
void LockHead::migratePartitionedLockHeads() {
invariant(partitioned());
// There can't be non-intent modes or conflicts when the lock is partitioned
invariant(!(grantedModes & ~intentModes) && !conflictModes);
// Migration time: lock each partition in turn and transfer its requests, if any
while (partitioned()) {
LockManager::Partition* partition = partitions.back();
stdx::lock_guard<SimpleMutex> scopedLock(partition->mutex);
LockManager::Partition::Map::iterator it = partition->data.find(resourceId);
if (it != partition->data.end()) {
PartitionedLockHead* partitionedLock = it->second;
while (!partitionedLock->grantedList.empty()) {
LockRequest* request = partitionedLock->grantedList._front;
partitionedLock->grantedList.remove(request);
request->partitionedLock = nullptr;
// Ordering is important here, as the next/prev fields are shared.
// Note that newRequest() will preserve the recursiveCount in this case
LockResult res = newRequest(request);
invariant(res == LOCK_OK); // Lock must still be granted
}
partition->data.erase(it);
delete partitionedLock;
}
// Don't pop-back to early as otherwise the lock will be considered not partitioned in
// newRequest().
partitions.pop_back();
}
}
//
// LockManager
//
// Have more buckets than CPUs to reduce contention on lock and caches
const unsigned LockManager::_numLockBuckets(128);
// Balance scalability of intent locks against potential added cost of conflicting locks.
// The exact value doesn't appear very important, but should be power of two
const unsigned LockManager::_numPartitions = 32;
// static
std::map<LockerId, BSONObj> LockManager::getLockToClientMap(ServiceContext* serviceContext) {
std::map<LockerId, BSONObj> lockToClientMap;
for (ServiceContext::LockedClientsCursor cursor(serviceContext);
Client* client = cursor.next();) {
invariant(client);
stdx::lock_guard<Client> lk(*client);
const OperationContext* clientOpCtx = client->getOperationContext();
// Operation context specific information
if (clientOpCtx) {
BSONObjBuilder infoBuilder;
// The client information
client->reportState(infoBuilder);
infoBuilder.append("opid", static_cast<int>(clientOpCtx->getOpID()));
LockerId lockerId = clientOpCtx->lockState()->getId();
lockToClientMap.insert({lockerId, infoBuilder.obj()});
}
}
return lockToClientMap;
}
LockManager::LockManager() {
_lockBuckets = new LockBucket[_numLockBuckets];
_partitions = new Partition[_numPartitions];
}
LockManager::~LockManager() {
cleanupUnusedLocks();
for (unsigned i = 0; i < _numLockBuckets; i++) {
// TODO: dump more information about the non-empty bucket to see what locks were leaked
invariant(_lockBuckets[i].data.empty());
}
delete[] _lockBuckets;
delete[] _partitions;
}
LockResult LockManager::lock(ResourceId resId, LockRequest* request, LockMode mode) {
// Sanity check that requests are not being reused without proper cleanup
invariant(request->recursiveCount == 1);
request->partitioned = (mode == MODE_IX || mode == MODE_IS);
request->mode = mode;
// For intent modes, try the PartitionedLockHead
if (request->partitioned) {
Partition* partition = _getPartition(request);
stdx::lock_guard<SimpleMutex> scopedLock(partition->mutex);
invariant(request->status == LockRequest::STATUS_NEW);
// Fast path for intent locks
PartitionedLockHead* partitionedLock = partition->find(resId);
if (partitionedLock) {
partitionedLock->newRequest(request);
return LOCK_OK;
}
// Unsuccessful: there was no PartitionedLockHead yet, so use regular LockHead.
// Must not hold any locks. It is OK for requests with intent modes to be on
// both a PartitionedLockHead and a regular LockHead, so the race here is benign.
}
// Use regular LockHead, maybe start partitioning
LockBucket* bucket = _getBucket(resId);
stdx::lock_guard<SimpleMutex> scopedLock(bucket->mutex);
invariant(request->status == LockRequest::STATUS_NEW);
LockHead* lock = bucket->findOrInsert(resId);
// Start a partitioned lock if possible
if (request->partitioned && !(lock->grantedModes & (~intentModes)) && !lock->conflictModes) {
Partition* partition = _getPartition(request);
stdx::lock_guard<SimpleMutex> scopedLock(partition->mutex);
PartitionedLockHead* partitionedLock = partition->findOrInsert(resId);
invariant(partitionedLock);
lock->partitions.push_back(partition);
partitionedLock->newRequest(request);
return LOCK_OK;
}
// For the first lock with a non-intent mode, migrate requests from partitioned lock heads
if (lock->partitioned()) {
lock->migratePartitionedLockHeads();
}
request->partitioned = false;
return lock->newRequest(request);
}
LockResult LockManager::convert(ResourceId resId, LockRequest* request, LockMode newMode) {
// If we are here, we already hold the lock in some mode. In order to keep it simple, we do
// not allow requesting a conversion while a lock is already waiting or pending conversion.
invariant(request->recursiveCount > 0);
request->recursiveCount++;
// Fast path for acquiring the same lock multiple times in modes, which are already covered
// by the current mode. It is safe to do this without locking, because 1) all calls for the
// same lock request must be done on the same thread and 2) if there are lock requests
// hanging off a given LockHead, then this lock will never disappear.
if ((LockConflictsTable[request->mode] | LockConflictsTable[newMode]) ==
LockConflictsTable[request->mode]) {
return LOCK_OK;
}
// TODO: For the time being we do not need conversions between unrelated lock modes (i.e.,
// modes which both add and remove to the conflicts set), so these are not implemented yet
// (e.g., S -> IX).
invariant((LockConflictsTable[request->mode] | LockConflictsTable[newMode]) ==
LockConflictsTable[newMode]);
LockBucket* bucket = _getBucket(resId);
stdx::lock_guard<SimpleMutex> scopedLock(bucket->mutex);
invariant(request->status == LockRequest::STATUS_GRANTED);
LockBucket::Map::iterator it = bucket->data.find(resId);
invariant(it != bucket->data.end());
LockHead* const lock = it->second;
if (lock->partitioned()) {
lock->migratePartitionedLockHeads();
}
// Construct granted mask without our current mode, so that it is not counted as
// conflicting
uint32_t grantedModesWithoutCurrentRequest = 0;
// We start the counting at 1 below, because LockModesCount also includes MODE_NONE
// at position 0, which can never be acquired/granted.
for (uint32_t i = 1; i < LockModesCount; i++) {
const uint32_t currentRequestHolds = (request->mode == static_cast<LockMode>(i) ? 1 : 0);
if (lock->grantedCounts[i] > currentRequestHolds) {
grantedModesWithoutCurrentRequest |= modeMask(static_cast<LockMode>(i));
}
}
// This check favours conversion requests over pending requests. For example:
//
// T1 requests lock L in IS
// T2 requests lock L in X
// T1 then upgrades L from IS -> S
//
// Because the check does not look into the conflict modes bitmap, it will grant L to
// T1 in S mode, instead of block, which would otherwise cause deadlock.
if (conflicts(newMode, grantedModesWithoutCurrentRequest)) {
request->status = LockRequest::STATUS_CONVERTING;
request->convertMode = newMode;
lock->conversionsCount++;
lock->incGrantedModeCount(request->convertMode);
return LOCK_WAITING;
} else { // No conflict, existing request
lock->incGrantedModeCount(newMode);
lock->decGrantedModeCount(request->mode);
request->mode = newMode;
return LOCK_OK;
}
}
bool LockManager::unlock(LockRequest* request) {
invariant(request->recursiveCount > 0);
request->recursiveCount--;
if (request->partitioned) {
// Unlocking a lock that was acquired as partitioned. The lock request may since have
// moved to the lock head, but there is no safe way to find out without synchronizing
// thorough the partition mutex. Migrations are expected to be rare.
Partition* partition = _getPartition(request);
stdx::lock_guard<SimpleMutex> scopedLock(partition->mutex);
invariant(request->status == LockRequest::STATUS_GRANTED ||
request->status == LockRequest::STATUS_CONVERTING);
if (request->status == LockRequest::STATUS_GRANTED && request->recursiveCount > 0)
return false;
// Fast path: still partitioned.
if (request->partitionedLock) {
request->partitionedLock->grantedList.remove(request);
return true;
}
// not partitioned anymore, fall through to regular case
}
invariant(request->lock);
LockHead* lock = request->lock;
LockBucket* bucket = _getBucket(lock->resourceId);
stdx::lock_guard<SimpleMutex> scopedLock(bucket->mutex);
if (request->status == LockRequest::STATUS_GRANTED) {
if (request->recursiveCount > 0)
return false;
// This releases a currently held lock and is the most common path, so it should be
// as efficient as possible. The fast path for decrementing multiple references did
// already ensure request->recursiveCount == 0.
// Remove from the granted list
lock->grantedList.remove(request);
lock->decGrantedModeCount(request->mode);
if (request->compatibleFirst) {
invariant(lock->compatibleFirstCount > 0);
lock->compatibleFirstCount--;
invariant(lock->compatibleFirstCount == 0 || !lock->grantedList.empty());
}
_onLockModeChanged(lock, lock->grantedCounts[request->mode] == 0);
} else if (request->status == LockRequest::STATUS_WAITING) {
// This cancels a pending lock request
invariant(request->recursiveCount == 0);
lock->conflictList.remove(request);
lock->decConflictModeCount(request->mode);
_onLockModeChanged(lock, true);
} else if (request->status == LockRequest::STATUS_CONVERTING) {
// This cancels a pending convert request
invariant(request->recursiveCount > 0);
invariant(lock->conversionsCount > 0);
// Lock only goes from GRANTED to CONVERTING, so cancelling the conversion request
// brings it back to the previous granted mode.
request->status = LockRequest::STATUS_GRANTED;
lock->conversionsCount--;
lock->decGrantedModeCount(request->convertMode);
request->convertMode = MODE_NONE;
_onLockModeChanged(lock, lock->grantedCounts[request->convertMode] == 0);
} else {
// Invalid request status
MONGO_UNREACHABLE;
}
return (request->recursiveCount == 0);
}
void LockManager::downgrade(LockRequest* request, LockMode newMode) {
invariant(request->lock);
invariant(request->recursiveCount > 0);
// The conflict set of the newMode should be a subset of the conflict set of the old mode.
// Can't downgrade from S -> IX for example.
invariant((LockConflictsTable[request->mode] | LockConflictsTable[newMode]) ==
LockConflictsTable[request->mode]);
LockHead* lock = request->lock;
LockBucket* bucket = _getBucket(lock->resourceId);
stdx::lock_guard<SimpleMutex> scopedLock(bucket->mutex);
invariant(request->status == LockRequest::STATUS_GRANTED);
lock->incGrantedModeCount(newMode);
lock->decGrantedModeCount(request->mode);
request->mode = newMode;
_onLockModeChanged(lock, true);
}
void LockManager::cleanupUnusedLocks() {
for (unsigned i = 0; i < _numLockBuckets; i++) {
LockBucket* bucket = &_lockBuckets[i];
stdx::lock_guard<SimpleMutex> scopedLock(bucket->mutex);
_cleanupUnusedLocksInBucket(bucket);
}
}
void LockManager::_cleanupUnusedLocksInBucket(LockBucket* bucket) {
LockBucket::Map::iterator it = bucket->data.begin();
size_t deletedLockHeads = 0;
while (it != bucket->data.end()) {
LockHead* lock = it->second;
if (lock->partitioned()) {
lock->migratePartitionedLockHeads();
}
if (lock->grantedModes == 0) {
invariant(lock->grantedModes == 0);
invariant(lock->grantedList._front == nullptr);
invariant(lock->grantedList._back == nullptr);
invariant(lock->conflictModes == 0);
invariant(lock->conflictList._front == nullptr);
invariant(lock->conflictList._back == nullptr);
invariant(lock->conversionsCount == 0);
invariant(lock->compatibleFirstCount == 0);
bucket->data.erase(it++);
deletedLockHeads++;
delete lock;
} else {
it++;
}
}
}
void LockManager::_onLockModeChanged(LockHead* lock, bool checkConflictQueue) {
// Unblock any converting requests (because conversions are still counted as granted and
// are on the granted queue).
for (LockRequest* iter = lock->grantedList._front;
(iter != nullptr) && (lock->conversionsCount > 0);
iter = iter->next) {
// Conversion requests are going in a separate queue
if (iter->status == LockRequest::STATUS_CONVERTING) {
invariant(iter->convertMode != 0);
// Construct granted mask without our current mode, so that it is not accounted as
// a conflict
uint32_t grantedModesWithoutCurrentRequest = 0;
// We start the counting at 1 below, because LockModesCount also includes
// MODE_NONE at position 0, which can never be acquired/granted.
for (uint32_t i = 1; i < LockModesCount; i++) {
const uint32_t currentRequestHolds =
(iter->mode == static_cast<LockMode>(i) ? 1 : 0);
const uint32_t currentRequestWaits =
(iter->convertMode == static_cast<LockMode>(i) ? 1 : 0);
// We cannot both hold and wait on the same lock mode
invariant(currentRequestHolds + currentRequestWaits <= 1);
if (lock->grantedCounts[i] > (currentRequestHolds + currentRequestWaits)) {
grantedModesWithoutCurrentRequest |= modeMask(static_cast<LockMode>(i));
}
}
if (!conflicts(iter->convertMode, grantedModesWithoutCurrentRequest)) {
lock->conversionsCount--;
lock->decGrantedModeCount(iter->mode);
iter->status = LockRequest::STATUS_GRANTED;
iter->mode = iter->convertMode;
iter->convertMode = MODE_NONE;
iter->notify->notify(lock->resourceId, LOCK_OK);
}
}
}
// Grant any conflicting requests, which might now be unblocked. Note that the loop below
// slightly violates fairness in that it will grant *all* compatible requests on the line even
// though there might be conflicting ones interspersed between them. For example, assume that an
// X lock was just freed and the conflict queue looks like this:
//
// IS -> IS -> X -> X -> S -> IS
//
// In strict FIFO, we should grant the first two IS modes and then stop when we reach the first
// X mode (the third request on the queue). However, the loop below would actually grant all IS
// + S modes and once they all drain it will grant X. The reason for this behaviour is
// increasing system throughput in the scenario where mutually compatible requests are
// interspersed with conflicting ones. For example, this would be a worst-case scenario for
// strict FIFO, because it would make the execution sequential:
//
// S -> X -> S -> X -> S -> X
LockRequest* iterNext = nullptr;
bool newlyCompatibleFirst = false; // Set on enabling compatibleFirst mode.
for (LockRequest* iter = lock->conflictList._front; (iter != nullptr) && checkConflictQueue;
iter = iterNext) {
invariant(iter->status == LockRequest::STATUS_WAITING);
// Store the actual next pointer, because we muck with the iter below and move it to
// the granted queue.
iterNext = iter->next;
if (conflicts(iter->mode, lock->grantedModes)) {
// If iter doesn't have a previous pointer, this means that it is at the front of the
// queue. If we continue scanning the queue beyond this point, we will starve it by
// granting more and more requests. However, if we newly transition to compatibleFirst
// mode, grant any waiting compatible requests.
if (!iter->prev && !newlyCompatibleFirst) {
break;
}
continue;
}
iter->status = LockRequest::STATUS_GRANTED;
// Remove from the conflicts list
lock->conflictList.remove(iter);
lock->decConflictModeCount(iter->mode);
// Add to the granted list
lock->grantedList.push_back(iter);
lock->incGrantedModeCount(iter->mode);
if (iter->compatibleFirst) {
newlyCompatibleFirst |= (lock->compatibleFirstCount++ == 0);
}
iter->notify->notify(lock->resourceId, LOCK_OK);
// Small optimization - nothing is compatible with a newly granted MODE_X, so no point in
// looking further in the conflict queue. Conflicting MODE_X requests are skipped above.
if (iter->mode == MODE_X) {
break;
}
}
// This is a convenient place to check that the state of the two request queues is in sync
// with the bitmask on the modes.
invariant((lock->grantedModes == 0) ^ (lock->grantedList._front != nullptr));
invariant((lock->conflictModes == 0) ^ (lock->conflictList._front != nullptr));
}
LockManager::LockBucket* LockManager::_getBucket(ResourceId resId) const {
return &_lockBuckets[resId % _numLockBuckets];
}
LockManager::Partition* LockManager::_getPartition(LockRequest* request) const {
return &_partitions[request->locker->getId() % _numPartitions];
}
void LockManager::dump() const {
BSONArrayBuilder locks;
_buildLocksArray(getLockToClientMap(getGlobalServiceContext()), true, nullptr, &locks);
LOGV2_OPTIONS(20521,
logv2::LogTruncation::Disabled,
"lock manager dump",
"addr"_attr = formatPtr(this),
"locks"_attr = locks.arr());
}
void LockManager::getLockInfoBSON(const std::map<LockerId, BSONObj>& lockToClientMap,
BSONObjBuilder* result) {
auto lockInfoArr = BSONArrayBuilder(result->subarrayStart("lockInfo"));
_buildLocksArray(lockToClientMap, false, this, &lockInfoArr);
}
void LockManager::_buildLocksArray(const std::map<LockerId, BSONObj>& lockToClientMap,
bool forLogging,
LockManager* mutableThis,
BSONArrayBuilder* locks) const {
for (size_t i = 0; i < _numLockBuckets; ++i) {
LockBucket& bucket = _lockBuckets[i];
stdx::lock_guard<SimpleMutex> scopedLock(bucket.mutex);
// LockInfo cleans the unused locks as it goes, but dump doesn't.
if (mutableThis) {
invariant(mutableThis == this);
mutableThis->_cleanupUnusedLocksInBucket(&bucket);
}
for (auto&& kv : bucket.data) {
const auto& lock = kv.second;
if (lock->grantedList.empty())
continue;
auto o = BSONObjBuilder(locks->subobjStart());
if (forLogging)
o.append("lockAddr", formatPtr(lock));
o.append("resourceId", lock->resourceId.toString());
struct {
StringData key;
LockRequest* iter;
} lists[] = {
{"granted"_sd, lock->grantedList._front},
{"pending"_sd, lock->conflictList._front},
};
for (auto [key, iter] : lists) {
auto arr = BSONArrayBuilder(o.subarrayStart(key));
for (; iter; iter = iter->next) {
auto req = BSONObjBuilder(arr.subobjStart());
if (forLogging) {
req.append("lockRequest", formatHex(iter->locker->getId()));
req.append("lockRequestAddr", formatPtr(iter->locker));
req.append("thread", formatThreadId(iter->locker->getThreadId()));
}
req.append("mode", modeName(iter->mode));
req.append("convertMode", modeName(iter->convertMode));
req.append("enqueueAtFront", iter->enqueueAtFront);
req.append("compatibleFirst", iter->compatibleFirst);
req.append("debugInfo", iter->locker->getDebugInfo());
if (auto it = lockToClientMap.find(iter->locker->getId());
it != lockToClientMap.end()) {
req.append("clientInfo", it->second);
}
}
}
}
}
}
PartitionedLockHead* LockManager::Partition::find(ResourceId resId) {
Map::iterator it = data.find(resId);
return it == data.end() ? nullptr : it->second;
}
PartitionedLockHead* LockManager::Partition::findOrInsert(ResourceId resId) {
PartitionedLockHead* lock;
Map::iterator it = data.find(resId);
if (it == data.end()) {
lock = new PartitionedLockHead();
lock->initNew(resId);
data.insert(Map::value_type(resId, lock));
} else {
lock = it->second;
}
return lock;
}
LockHead* LockManager::LockBucket::findOrInsert(ResourceId resId) {
LockHead* lock;
Map::iterator it = data.find(resId);
if (it == data.end()) {
lock = new LockHead();
lock->initNew(resId);
data.insert(Map::value_type(resId, lock));
} else {
lock = it->second;
}
return lock;
}
//
// ResourceId
//
std::string ResourceId::toString() const {
StringBuilder ss;
ss << "{" << _fullHash << ": " << resourceTypeName(getType()) << ", " << getHashId();
if (getType() == RESOURCE_MUTEX) {
ss << ", " << Lock::ResourceMutex::getName(*this);
}
if (getType() == RESOURCE_DATABASE || getType() == RESOURCE_COLLECTION) {
auto catalog = CollectionCatalog::get(getGlobalServiceContext());
boost::optional<std::string> resourceName = catalog->lookupResourceName(*this);
if (resourceName) {
ss << ", " << *resourceName;
}
}
ss << "}";
return ss.str();
}
//
// LockRequest
//
void LockRequest::initNew(Locker* locker, LockGrantNotification* notify) {
this->locker = locker;
this->notify = notify;
enqueueAtFront = false;
compatibleFirst = false;
recursiveCount = 1;
lock = nullptr;
partitionedLock = nullptr;
prev = nullptr;
next = nullptr;
status = STATUS_NEW;
partitioned = false;
mode = MODE_NONE;
convertMode = MODE_NONE;
unlockPending = 0;
}
//
// Helper calls
//
const char* modeName(LockMode mode) {
return LockModeNames[mode];
}
const char* legacyModeName(LockMode mode) {
return LegacyLockModeNames[mode];
}
bool isModeCovered(LockMode mode, LockMode coveringMode) {
return (LockConflictsTable[coveringMode] | LockConflictsTable[mode]) ==
LockConflictsTable[coveringMode];
}
const char* lockRequestStatusName(LockRequest::Status status) {
return LockRequestStatusNames[status];
}
} // namespace mongo
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