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d_concurrency.h
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d_concurrency.h
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/**
* Copyright (C) 2008-2014 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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.
*/
#pragma once
#include <climits> // For UINT_MAX
#include "mongo/db/concurrency/locker.h"
#include "mongo/db/operation_context.h"
#include "mongo/util/timer.h"
namespace mongo {
class StringData;
class NamespaceString;
//注意d_concurrency.h中的lock类和locker.h中的locker类的区别
class Lock {
public:
/**
* NOTE: DO NOT add any new usages of TempRelease. It is being deprecated/removed.
*/
class TempRelease {
MONGO_DISALLOW_COPYING(TempRelease);
public:
explicit TempRelease(Locker* lockState);
~TempRelease();
private:
// Not owned
Locker* const _lockState;
// If _locksReleased is true, this stores the persisted lock information to be restored
// in the destructor. Otherwise it is empty.
Locker::LockSnapshot _lockSnapshot;
// False if locks could not be released because of recursive locking
const bool _locksReleased;
};
/**
* General purpose RAII wrapper for a resource managed by the lock manager
*
* See LockMode for the supported modes. Unlike DBLock/Collection lock, this will not do
* any additional checks/upgrades or global locking. Use ResourceLock for locking
* resources other than RESOURCE_GLOBAL, RESOURCE_DATABASE and RESOURCE_COLLECTION.
*/
//GlobalLock._pbwm
//ExclusiveLock继承该类
class ResourceLock {
MONGO_DISALLOW_COPYING(ResourceLock);
public:
ResourceLock(Locker* locker, ResourceId rid)
: _rid(rid), _locker(locker), _result(LOCK_INVALID) {}
ResourceLock(Locker* locker, ResourceId rid, LockMode mode)
: _rid(rid), _locker(locker), _result(LOCK_INVALID) {
//Lock::ResourceLock::lock
lock(mode);
}
ResourceLock(ResourceLock&& otherLock)
: _rid(otherLock._rid), _locker(otherLock._locker), _result(otherLock._result) {
// Mark as moved so the destructor doesn't invalidate the newly-
// constructed lock.
otherLock._result = LOCK_INVALID;
}
~ResourceLock() {
if (isLocked()) {
unlock();
}
}
void lock(LockMode mode);
void unlock();
bool isLocked() const {
return _result == LOCK_OK;
}
private:
const ResourceId _rid;
Locker* const _locker;
LockResult _result;
};
class SharedLock;
class ExclusiveLock;
/**
* For use as general mutex or readers/writers lock, outside the general multi-granularity
* model. A ResourceMutex is not affected by yielding/temprelease and two phase locking
* semantics inside WUOWs. Lock with ResourceLock, SharedLock or ExclusiveLock. Uses same
* fairness as other LockManager locks.
*/
//该类主要就是通过Lock::ResourceMutex::ResourceMutex构造函数中调用
// ResourceIdFactory::newResourceIdForMutex自动生成一个RESOURCE_MUTEX类型的
// ResourceId,其hashid值单调递增
class ResourceMutex {
public:
ResourceMutex(std::string resourceLabel);
std::string getName() const {
return getName(_rid);
};
static std::string getName(ResourceId resourceId);
bool isExclusivelyLocked(Locker* locker);
bool isAtLeastReadLocked(Locker* locker);
private:
friend class Lock::SharedLock;
friend class Lock::ExclusiveLock;
/**
* Each instantiation of this class allocates a new ResourceId.
*/
ResourceId rid() const {
return _rid;
}
const ResourceId _rid;
};
/**
* Obtains a ResourceMutex for exclusive use.
*/
//排他锁,MODE_X封装
//用的比较少,独占锁
class ExclusiveLock : public ResourceLock {
public:
ExclusiveLock(Locker* locker, ResourceMutex mutex)
: ResourceLock(locker, mutex.rid(), MODE_X) {}
};
/**
* Obtains a ResourceMutex for shared/non-exclusive use. This uses MODE_IS rather than MODE_S
* to take advantage of optimizations in the lock manager for intent modes. This is OK as
* this just has to conflict with exclusive locks.
*/
//共享锁,MODE_IS封装
//用的比较少
class SharedLock : public ResourceLock {
public:
SharedLock(Locker* locker, ResourceMutex mutex)
: ResourceLock(locker, mutex.rid(), MODE_IS) {}
};
/**
* Global lock.
*
* Grabs global resource lock. Allows further (recursive) acquisition of the global lock
* in any mode, see LockMode. An outermost GlobalLock calls abandonSnapshot() on destruction, so
* that the storage engine can release resources, such as snapshots or locks, that it may have
* acquired during the transaction. Note that any writes are committed in nested WriteUnitOfWork
* scopes, so write conflicts cannot happen when releasing the GlobalLock.
*
* NOTE: Does not acquire flush lock.
*/
//全局锁使用可以参考 lock_stat_test.cpp中的测试用例
//GlobalWrite GlobalrRead全局读锁和全局写锁继承该类
class GlobalLock { //DBLock._globalLock
public:
class EnqueueOnly {};
GlobalLock(OperationContext* opCtx, LockMode lockMode, unsigned timeoutMs);
GlobalLock(GlobalLock&&);
/**
* Enqueues lock but does not block on lock acquisition.
* Call waitForLock() to complete locking process.
*
* Does not set that the global lock was taken on the GlobalLockAcquisitionTracker. Call
* waitForLock to do so.
*/
GlobalLock(OperationContext* opCtx,
LockMode lockMode,
unsigned timeoutMs,
EnqueueOnly enqueueOnly);
~GlobalLock() {
if (_result != LOCK_INVALID) {
if (isLocked() && _isOutermostLock) {
//WiredTigerRecoveryUnit::abandonSnapshot
_opCtx->recoveryUnit()->abandonSnapshot();
}
_unlock();
}
}
/**
* Waits for lock to be granted. Sets that the global lock was taken on the
* GlobalLockAcquisitionTracker.
*/
void waitForLock(unsigned timeoutMs);
bool isLocked() const {
return _result == LOCK_OK;
}
private:
void _enqueue(LockMode lockMode, unsigned timeoutMs);
void _unlock();
//其中操作_opCtx的_locker就是locker类型
OperationContext* const _opCtx;
LockResult _result; //lock是否成功等
//赋值见Lock::GlobalLock::GlobalLock
ResourceLock _pbwm;
const bool _isOutermostLock;
//对应的资源信息为resourceIdGlobal,参考LockerImpl<>::_lockGlobalBegin
};
/**
* Global exclusive lock
*
* Allows exclusive write access to all databases and collections, blocking all other
* access. Allows further (recursive) acquisition of the global lock in any mode,
* see LockMode.
*/
class GlobalWrite : public GlobalLock {
public:
explicit GlobalWrite(OperationContext* opCtx, unsigned timeoutMs = UINT_MAX)
: GlobalLock(opCtx, MODE_X, timeoutMs) {
if (isLocked()) {
opCtx->lockState()->lockMMAPV1Flush();
}
}
};
/**
* Global shared lock
*
* Allows concurrent read access to all databases and collections, blocking any writers.
* Allows further (recursive) acquisition of the global lock in shared (S) or intent-shared
* (IS) mode, see LockMode.
*/
class GlobalRead : public GlobalLock {
public:
explicit GlobalRead(OperationContext* opCtx, unsigned timeoutMs = UINT_MAX)
: GlobalLock(opCtx, MODE_S, timeoutMs) {
if (isLocked()) {
opCtx->lockState()->lockMMAPV1Flush();
}
}
};
/**
* Database lock with support for collection- and document-level locking
*
* This lock supports four modes (see Lock_Mode):
* MODE_IS: concurrent database access, requiring further collection read locks
* MODE_IX: concurrent database access, requiring further collection read or write locks
* MODE_S: shared read access to the database, blocking any writers
* MODE_X: exclusive access to the database, blocking all other readers and writers
*
* For MODE_IS or MODE_S also acquires global lock in intent-shared (IS) mode, and
* for MODE_IX or MODE_X also acquires global lock in intent-exclusive (IX) mode.
* For storage engines that do not support collection-level locking, MODE_IS will be
* upgraded to MODE_S and MODE_IX will be upgraded to MODE_X.
*/
/*
Primary 上写入文档时,首先对写入的 DB 加写意向锁,再对集合加写意向锁,然后调用底层引擎接口写入文档,
对 local 数据库加写意向锁,对oplog.rs集合加写意向锁,写入 oplog:
DBLock("db1", MODE_IX);
CollectionLock("collection1", MODE_IX);
storageEngine.writeDocument(...);
DBLock("local", MODEX_IX);
CollectionLock("oplog.rs", MODEX_IX);
storageEngine.writeOplog(...);
*/
//AutoGetDb._dbLock为该类型,
//AutoGetOrCreateDb::AutoGetOrCreateDb AutoGetCollection::AutoGetCollection
// 及AutoGetDb::AutoGetDb中构造使用
//库锁封装过程有两种:
// 第一种:
// DBLock("db1", MODE_IX); //其中库锁中先对全局资源类型RESOURCE_GLOBAL加锁,然后对RESOURCE_DATABASE加锁
// CollectionLock("collection1", MODE_IX);
//
// 第二种:
// AutoGetCollection::AutoGetCollection AutoGetCollectionForRead::AutoGetCollectionForRead这两个类
// 初始化构造会同时封装库锁和表锁
//读: FindCmd::run中实现查询的库锁、表锁加锁过程
//增:insertBatchAndHandleErrors中实现查询的库锁、表锁加锁过程
//删:performSingleDeleteOp中实现查询的库锁、表锁加锁过程
//改:performSingleUpdateOp中实现查询的库锁、表锁加锁过程
//AutoGetDb._dbLock为该类型,每个库DB都对应有一个DBLock
class DBLock {
public:
DBLock(OperationContext* opCtx, StringData db, LockMode mode);
DBLock(DBLock&&);
~DBLock();
/**
* Releases the DBLock and reacquires it with the new mode. The global intent
* lock is retained (so the database can't disappear). Relocking from MODE_IS or
* MODE_S to MODE_IX or MODE_X is not allowed to avoid violating the global intent.
* Use relockWithMode() instead of upgrading to avoid deadlock.
*/
void relockWithMode(LockMode newMode);
private:
const ResourceId _id;
OperationContext* const _opCtx;
// May be changed through relockWithMode. The global lock mode won't change though,
// because we never change from IS/S to IX/X or vice versa, just convert locks from
// IX -> X.
LockMode _mode;
// Acquires the global lock on our behalf.
//Lock::DBLock::DBLock中构造
GlobalLock _globalLock;
};
/**
* Collection lock with support for document-level locking
*
* This lock supports four modes (see Lock_Mode):
* MODE_IS: concurrent collection access, requiring document level locking read locks
* MODE_IX: concurrent collection access, requiring document level read or write locks
* MODE_S: shared read access to the collection, blocking any writers
* MODE_X: exclusive access to the collection, blocking all other readers and writers
*
* An appropriate DBLock must already be held before locking a collection: it is an error,
* checked with a dassert(), to not have a suitable database lock before locking the
* collection. For storage engines that do not support document-level locking, MODE_IS
* will be upgraded to MODE_S and MODE_IX will be upgraded to MODE_X.
*/
/*
Primary 上写入文档时,首先对写入的 DB 加写意向锁,再对集合加写意向锁,然后调用底层引擎接口写入文档,
对 local 数据库加写意向锁,对oplog.rs集合加写意向锁,写入 oplog:
DBLock("db1", MODE_IX);
CollectionLock("collection1", MODE_IX);
storageEngine.writeDocument(...);
DBLock("local", MODEX_IX);
CollectionLock("oplog.rs", MODEX_IX);
storageEngine.writeOplog(...);
*/
//读: FindCmd::run中实现查询的库锁、表锁加锁过程
//增:insertBatchAndHandleErrors中实现查询的库锁、表锁加锁过程
//删:performSingleDeleteOp中实现查询的库锁、表锁加锁过程
//改:performSingleUpdateOp中实现查询的库锁、表锁加锁过程
//库锁封装过程有两种:
// 第一种:
// DBLock("db1", MODE_IX); //其中库锁中先对全局资源类型RESOURCE_GLOBAL加锁,然后对RESOURCE_DATABASE加锁
// CollectionLock("collection1", MODE_IX);
//
// 第二种:
// AutoGetCollection::AutoGetCollection AutoGetCollectionForRead::AutoGetCollectionForRead这两个类
// 初始化构造会同时封装库锁和表锁
//AutoGetCollection._collLock为该类型,每个表collection都对应有一个CollectionLock
//AutoGetCollection::AutoGetCollection AutoGetCollectionForRead::AutoGetCollectionForRead这两个类
// 初始化构造会同时封装库锁和表锁
class CollectionLock {
MONGO_DISALLOW_COPYING(CollectionLock);
public:
CollectionLock(Locker* lockState, StringData ns, LockMode mode);
~CollectionLock();
/**
* When holding the collection in MODE_IX or MODE_X, calling this will release the
* collection and database locks, and relocks the database in MODE_X. This is typically
* used if the collection still needs to be created. Upgrading would not be safe as
* it could lead to deadlock, similarly for relocking the database without releasing
* the collection lock. The collection lock will also be reacquired even though it is
* not really needed, as it simplifies invariant checking: the CollectionLock class
* has as invariant that a collection lock is being held.
*/
void relockAsDatabaseExclusive(Lock::DBLock& dbLock);
private:
const ResourceId _id;
Locker* const _lockState;
};
/**
* Like the CollectionLock, but optimized for the local oplog. Always locks in MODE_IX,
* must call serializeIfNeeded() before doing any concurrent operations in order to
* support storage engines without document level locking. It is an error, checked with a
* dassert(), to not have a suitable database lock when taking this lock.
*/
class OplogIntentWriteLock {
MONGO_DISALLOW_COPYING(OplogIntentWriteLock);
public:
explicit OplogIntentWriteLock(Locker* lockState);
~OplogIntentWriteLock();
void serializeIfNeeded();
private:
Locker* const _lockState;
bool _serialized;
};
/**
* Turn on "parallel batch writer mode" by locking the global ParallelBatchWriterMode
* resource in exclusive mode. This mode is off by default.
* Note that only one thread creates a ParallelBatchWriterMode object; the other batch
* writers just call setShouldConflictWithSecondaryBatchApplication(false).
*/
class ParallelBatchWriterMode {
MONGO_DISALLOW_COPYING(ParallelBatchWriterMode);
public:
explicit ParallelBatchWriterMode(Locker* lockState);
~ParallelBatchWriterMode();
private:
ResourceLock _pbwm;
Locker* const _lockState;
const bool _orginalShouldConflict;
};
};
}