| /* |
| * Copyright (C) 2007, 2008, 2013 Apple Inc. All rights reserved. |
| * |
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| * modification, are permitted provided that the following conditions |
| * are met: |
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| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
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| * from this software without specific prior written permission. |
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| |
| #include "config.h" |
| #include "SQLTransactionBackend.h" |
| |
| #include "Database.h" |
| #include "DatabaseAuthorizer.h" |
| #include "DatabaseContext.h" |
| #include "DatabaseThread.h" |
| #include "DatabaseTracker.h" |
| #include "Logging.h" |
| #include "OriginLock.h" |
| #include "SQLError.h" |
| #include "SQLStatement.h" |
| #include "SQLStatementCallback.h" |
| #include "SQLStatementErrorCallback.h" |
| #include "SQLTransaction.h" |
| #include "SQLTransactionCoordinator.h" |
| #include "SQLiteTransaction.h" |
| #include <wtf/StdLibExtras.h> |
| #include <wtf/text/WTFString.h> |
| |
| |
| // How does a SQLTransaction work? |
| // ============================== |
| // The SQLTransaction is a state machine that executes a series of states / steps. |
| // |
| // The work of the transaction states are defined in section of 4.3.2 of the |
| // webdatabase spec: http://dev.w3.org/html5/webdatabase/#processing-model |
| // |
| // the State Transition Graph at a glance: |
| // ====================================== |
| // |
| // Backend . Frontend |
| // (works with SQLiteDatabase) . (works with Script) |
| // =========================== . =================== |
| // . |
| // 1. Idle . |
| // v . |
| // 2. AcquireLock . |
| // v . |
| // 3. OpenTransactionAndPreflight ------------------------------------------. |
| // | . | |
| // `-------------------------------> 8. DeliverTransactionCallback --. | |
| // . | v v |
| // ,-------------------------------------' 9. DeliverTransactionErrorCallback + |
| // | . ^ ^ ^ | |
| // v . | | | | |
| // 4. RunStatements -----------------------------------------------------' | | | |
| // | ^ ^ | ^ | . | | | |
| // |--------' | | | `------------> 10. DeliverStatementCallback +-----' | | |
| // | | | `---------------------------------------------' | | |
| // | | `-----------------> 11. DeliverQuotaIncreaseCallback + | | |
| // | `-----------------------------------------------------' | | |
| // v . | | |
| // 5. PostflightAndCommit --+--------------------------------------------------' | |
| // |----------> 12. DeliverSuccessCallback + | |
| // ,--------------------' . | | |
| // v . | | |
| // 6. CleanupAndTerminate <-----------------------------------------' | |
| // v ^ . | |
| // 0. End | . | |
| // | . | |
| // 7: CleanupAfterTransactionErrorCallback <----------------------------' |
| // . |
| // |
| // the States and State Transitions: |
| // ================================ |
| // 0. SQLTransactionState::End |
| // - the end state. |
| // |
| // 1. SQLTransactionState::Idle |
| // - placeholder state while waiting on frontend/backend, etc. See comment on |
| // "State transitions between SQLTransaction and SQLTransactionBackend" |
| // below. |
| // |
| // 2. SQLTransactionState::AcquireLock (runs in backend) |
| // - this is the start state. |
| // - acquire the "lock". |
| // - on "lock" acquisition, goto SQLTransactionState::OpenTransactionAndPreflight. |
| // |
| // 3. SQLTransactionState::openTransactionAndPreflight (runs in backend) |
| // - Sets up an SQLiteTransaction. |
| // - begin the SQLiteTransaction. |
| // - call the SQLTransactionWrapper preflight if available. |
| // - schedule script callback. |
| // - on error, goto SQLTransactionState::DeliverTransactionErrorCallback. |
| // - goto SQLTransactionState::DeliverTransactionCallback. |
| // |
| // 4. SQLTransactionState::DeliverTransactionCallback (runs in frontend) |
| // - invoke the script function callback() if available. |
| // - on error, goto SQLTransactionState::DeliverTransactionErrorCallback. |
| // - goto SQLTransactionState::RunStatements. |
| // |
| // 5. SQLTransactionState::DeliverTransactionErrorCallback (runs in frontend) |
| // - invoke the script function errorCallback if available. |
| // - goto SQLTransactionState::CleanupAfterTransactionErrorCallback. |
| // |
| // 6. SQLTransactionState::RunStatements (runs in backend) |
| // - while there are statements { |
| // - run a statement. |
| // - if statementCallback is available, goto SQLTransactionState::DeliverStatementCallback. |
| // - on error, |
| // goto SQLTransactionState::DeliverQuotaIncreaseCallback, or |
| // goto SQLTransactionState::DeliverStatementCallback, or |
| // goto SQLTransactionState::deliverTransactionErrorCallback. |
| // } |
| // - goto SQLTransactionState::PostflightAndCommit. |
| // |
| // 7. SQLTransactionState::DeliverStatementCallback (runs in frontend) |
| // - invoke script statement callback (assume available). |
| // - on error, goto SQLTransactionState::DeliverTransactionErrorCallback. |
| // - goto SQLTransactionState::RunStatements. |
| // |
| // 8. SQLTransactionState::DeliverQuotaIncreaseCallback (runs in frontend) |
| // - give client a chance to increase the quota. |
| // - goto SQLTransactionState::RunStatements. |
| // |
| // 9. SQLTransactionState::PostflightAndCommit (runs in backend) |
| // - call the SQLTransactionWrapper postflight if available. |
| // - commit the SQLiteTansaction. |
| // - on error, goto SQLTransactionState::DeliverTransactionErrorCallback. |
| // - if successCallback is available, goto SQLTransactionState::DeliverSuccessCallback. |
| // else goto SQLTransactionState::CleanupAndTerminate. |
| // |
| // 10. SQLTransactionState::DeliverSuccessCallback (runs in frontend) |
| // - invoke the script function successCallback() if available. |
| // - goto SQLTransactionState::CleanupAndTerminate. |
| // |
| // 11. SQLTransactionState::CleanupAndTerminate (runs in backend) |
| // - stop and clear the SQLiteTransaction. |
| // - release the "lock". |
| // - goto SQLTransactionState::End. |
| // |
| // 12. SQLTransactionState::CleanupAfterTransactionErrorCallback (runs in backend) |
| // - rollback the SQLiteTransaction. |
| // - goto SQLTransactionState::CleanupAndTerminate. |
| // |
| // State transitions between SQLTransaction and SQLTransactionBackend |
| // ================================================================== |
| // As shown above, there are state transitions that crosses the boundary between |
| // the frontend and backend. For example, |
| // |
| // OpenTransactionAndPreflight (state 3 in the backend) |
| // transitions to DeliverTransactionCallback (state 8 in the frontend), |
| // which in turn transitions to RunStatements (state 4 in the backend). |
| // |
| // This cross boundary transition is done by posting transition requests to the |
| // other side and letting the other side's state machine execute the state |
| // transition in the appropriate thread (i.e. the script thread for the frontend, |
| // and the database thread for the backend). |
| // |
| // Logically, the state transitions work as shown in the graph above. But |
| // physically, the transition mechanism uses the Idle state (both in the frontend |
| // and backend) as a waiting state for further activity. For example, taking a |
| // closer look at the 3 state transition example above, what actually happens |
| // is as follows: |
| // |
| // Step 1: |
| // ====== |
| // In the frontend thread: |
| // - waiting quietly is Idle. Not doing any work. |
| // |
| // In the backend: |
| // - is in OpenTransactionAndPreflight, and doing its work. |
| // - when done, it transits to the backend DeliverTransactionCallback. |
| // - the backend DeliverTransactionCallback sends a request to the frontend |
| // to transit to DeliverTransactionCallback, and then itself transits to |
| // Idle. |
| // |
| // Step 2: |
| // ====== |
| // In the frontend thread: |
| // - transits to DeliverTransactionCallback and does its work. |
| // - when done, it transits to the frontend RunStatements. |
| // - the frontend RunStatements sends a request to the backend to transit |
| // to RunStatements, and then itself transits to Idle. |
| // |
| // In the backend: |
| // - waiting quietly in Idle. |
| // |
| // Step 3: |
| // ====== |
| // In the frontend thread: |
| // - waiting quietly is Idle. Not doing any work. |
| // |
| // In the backend: |
| // - transits to RunStatements, and does its work. |
| // ... |
| // |
| // So, when the frontend or backend are not active, they will park themselves in |
| // their Idle states. This means their m_nextState is set to Idle, but they never |
| // actually run the corresponding state function. Note: for both the frontend and |
| // backend, the state function for Idle is unreachableState(). |
| // |
| // The states that send a request to their peer across the front/back boundary |
| // are implemented with just 2 functions: SQLTransaction::sendToBackendState() |
| // and SQLTransactionBackend::sendToFrontendState(). These state functions do |
| // nothing but sends a request to the other side to transit to the current |
| // state (indicated by m_nextState), and then transits itself to the Idle state |
| // to wait for further action. |
| |
| |
| // The Life-Cycle of a SQLTransaction i.e. Who's keeping the SQLTransaction alive? |
| // ============================================================================== |
| // The RefPtr chain goes something like this: |
| // |
| // At birth (in DatabaseBackend::runTransaction()): |
| // ==================================================== |
| // DatabaseBackend // Deque<RefPtr<SQLTransactionBackend>> m_transactionQueue points to ... |
| // --> SQLTransactionBackend // RefPtr<SQLTransaction> m_frontend points to ... |
| // --> SQLTransaction // RefPtr<SQLTransactionBackend> m_backend points to ... |
| // --> SQLTransactionBackend // which is a circular reference. |
| // |
| // Note: there's a circular reference between the SQLTransaction front-end and |
| // back-end. This circular reference is established in the constructor of the |
| // SQLTransactionBackend. The circular reference will be broken by calling |
| // doCleanup() to nullify m_frontend. This is done at the end of the transaction's |
| // clean up state (i.e. when the transaction should no longer be in use thereafter), |
| // or if the database was interrupted. See comments on "What happens if a transaction |
| // is interrupted?" below for details. |
| // |
| // After scheduling the transaction with the DatabaseThread (DatabaseBackend::scheduleTransaction()): |
| // ====================================================================================================== |
| // DatabaseThread // MessageQueue<DatabaseTask> m_queue points to ... |
| // --> DatabaseTransactionTask // RefPtr<SQLTransactionBackend> m_transaction points to ... |
| // --> SQLTransactionBackend // RefPtr<SQLTransaction> m_frontend points to ... |
| // --> SQLTransaction // RefPtr<SQLTransactionBackend> m_backend points to ... |
| // --> SQLTransactionBackend // which is a circular reference. |
| // |
| // When executing the transaction (in DatabaseThread::databaseThread()): |
| // ==================================================================== |
| // std::unique_ptr<DatabaseTask> task; // points to ... |
| // --> DatabaseTransactionTask // RefPtr<SQLTransactionBackend> m_transaction points to ... |
| // --> SQLTransactionBackend // RefPtr<SQLTransaction> m_frontend; |
| // --> SQLTransaction // RefPtr<SQLTransactionBackend> m_backend points to ... |
| // --> SQLTransactionBackend // which is a circular reference. |
| // |
| // At the end of cleanupAndTerminate(): |
| // =================================== |
| // At the end of the cleanup state, the SQLTransactionBackend::m_frontend is nullified. |
| // If by then, a JSObject wrapper is referring to the SQLTransaction, then the reference |
| // chain looks like this: |
| // |
| // JSObjectWrapper |
| // --> SQLTransaction // in RefPtr<SQLTransactionBackend> m_backend points to ... |
| // --> SQLTransactionBackend // which no longer points back to its SQLTransaction. |
| // |
| // When the GC collects the corresponding JSObject, the above chain will be cleaned up |
| // and deleted. |
| // |
| // If there is no JSObject wrapper referring to the SQLTransaction when the cleanup |
| // states nullify SQLTransactionBackend::m_frontend, the SQLTransaction will deleted then. |
| // However, there will still be a DatabaseTask pointing to the SQLTransactionBackend (see |
| // the "When executing the transaction" chain above). This will keep the |
| // SQLTransactionBackend alive until DatabaseThread::databaseThread() releases its |
| // task std::unique_ptr. |
| // |
| // What happens if a transaction is interrupted? |
| // ============================================ |
| // If the transaction is interrupted half way, it won't get to run to state |
| // CleanupAndTerminate, and hence, would not have called SQLTransactionBackend's |
| // doCleanup(). doCleanup() is where we nullify SQLTransactionBackend::m_frontend |
| // to break the reference cycle between the frontend and backend. Hence, we need |
| // to cleanup the transaction by other means. |
| // |
| // Note: calling SQLTransactionBackend::notifyDatabaseThreadIsShuttingDown() |
| // is effectively the same as calling SQLTransactionBackend::doClean(). |
| // |
| // In terms of who needs to call doCleanup(), there are 5 phases in the |
| // SQLTransactionBackend life-cycle. These are the phases and how the clean |
| // up is done: |
| // |
| // Phase 1. After Birth, before scheduling |
| // |
| // - To clean up, DatabaseThread::databaseThread() will call |
| // DatabaseBackend::close() during its shutdown. |
| // - DatabaseBackend::close() will iterate |
| // DatabaseBackend::m_transactionQueue and call |
| // notifyDatabaseThreadIsShuttingDown() on each transaction there. |
| // |
| // Phase 2. After scheduling, before state AcquireLock |
| // |
| // - If the interruption occures before the DatabaseTransactionTask is |
| // scheduled in DatabaseThread::m_queue but hasn't gotten to execute |
| // (i.e. DatabaseTransactionTask::performTask() has not been called), |
| // then the DatabaseTransactionTask may get destructed before it ever |
| // gets to execute. |
| // - To clean up, the destructor will check if the task's m_wasExecuted is |
| // set. If not, it will call notifyDatabaseThreadIsShuttingDown() on |
| // the task's transaction. |
| // |
| // Phase 3. After state AcquireLock, before "lockAcquired" |
| // |
| // - In this phase, the transaction would have been added to the |
| // SQLTransactionCoordinator's CoordinationInfo's pendingTransactions. |
| // - To clean up, during shutdown, DatabaseThread::databaseThread() calls |
| // SQLTransactionCoordinator::shutdown(), which calls |
| // notifyDatabaseThreadIsShuttingDown(). |
| // |
| // Phase 4: After "lockAcquired", before state CleanupAndTerminate |
| // |
| // - In this phase, the transaction would have been added either to the |
| // SQLTransactionCoordinator's CoordinationInfo's activeWriteTransaction |
| // or activeReadTransactions. |
| // - To clean up, during shutdown, DatabaseThread::databaseThread() calls |
| // SQLTransactionCoordinator::shutdown(), which calls |
| // notifyDatabaseThreadIsShuttingDown(). |
| // |
| // Phase 5: After state CleanupAndTerminate |
| // |
| // - This is how a transaction ends normally. |
| // - state CleanupAndTerminate calls doCleanup(). |
| |
| namespace WebCore { |
| |
| SQLTransactionBackend::SQLTransactionBackend(SQLTransaction& frontend) |
| : m_frontend(frontend) |
| { |
| m_requestedState = SQLTransactionState::AcquireLock; |
| } |
| |
| SQLTransactionBackend::~SQLTransactionBackend() |
| { |
| ASSERT(!m_frontend.m_sqliteTransaction); |
| } |
| |
| void SQLTransactionBackend::doCleanup() |
| { |
| ASSERT(m_frontend.database().databaseThread().getThread() == &Thread::current()); |
| |
| m_frontend.releaseOriginLockIfNeeded(); |
| |
| LockHolder locker(m_frontend.m_statementMutex); |
| m_frontend.m_statementQueue.clear(); |
| |
| if (m_frontend.m_sqliteTransaction) { |
| // In the event we got here because of an interruption or error (i.e. if |
| // the transaction is in progress), we should roll it back here. Clearing |
| // m_sqliteTransaction invokes SQLiteTransaction's destructor which does |
| // just that. We might as well do this unconditionally and free up its |
| // resources because we're already terminating. |
| m_frontend.m_sqliteTransaction = nullptr; |
| } |
| |
| // Release the lock on this database |
| if (m_frontend.m_lockAcquired) |
| m_frontend.m_database->transactionCoordinator()->releaseLock(m_frontend); |
| |
| // Do some aggresive clean up here except for m_database. |
| // |
| // We can't clear m_database here because the frontend may asynchronously |
| // invoke SQLTransactionBackend::requestTransitToState(), and that function |
| // uses m_database to schedule a state transition. This may occur because |
| // the frontend (being in another thread) may already be on the way to |
| // requesting our next state before it detects an interruption. |
| // |
| // There is no harm in letting it finish making the request. It'll set |
| // m_requestedState, but we won't execute a transition to that state because |
| // we've already shut down the transaction. |
| // |
| // We also can't clear m_currentStatementBackend and m_transactionError. |
| // m_currentStatementBackend may be accessed asynchronously by the |
| // frontend's deliverStatementCallback() state. Similarly, |
| // m_transactionError may be accessed by deliverTransactionErrorCallback(). |
| // This occurs if requests for transition to those states have already been |
| // registered with the frontend just prior to a clean up request arriving. |
| // |
| // So instead, let our destructor handle their clean up since this |
| // SQLTransactionBackend is guaranteed to not destruct until the frontend |
| // is also destructing. |
| |
| m_frontend.m_wrapper = nullptr; |
| } |
| |
| SQLTransactionBackend::StateFunction SQLTransactionBackend::stateFunctionFor(SQLTransactionState state) |
| { |
| static const StateFunction stateFunctions[] = { |
| &SQLTransactionBackend::unreachableState, // 0. end |
| &SQLTransactionBackend::unreachableState, // 1. idle |
| &SQLTransactionBackend::acquireLock, // 2. |
| &SQLTransactionBackend::openTransactionAndPreflight, // 3. |
| &SQLTransactionBackend::runStatements, // 4. |
| &SQLTransactionBackend::unreachableState, // 5. postflightAndCommit |
| &SQLTransactionBackend::cleanupAndTerminate, // 6. |
| &SQLTransactionBackend::cleanupAfterTransactionErrorCallback, // 7. |
| &SQLTransactionBackend::unreachableState, // 8. deliverTransactionCallback |
| &SQLTransactionBackend::unreachableState, // 9. deliverTransactionErrorCallback |
| &SQLTransactionBackend::unreachableState, // 10. deliverStatementCallback |
| &SQLTransactionBackend::unreachableState, // 11. deliverQuotaIncreaseCallback |
| &SQLTransactionBackend::unreachableState // 12. deliverSuccessCallback |
| }; |
| |
| ASSERT(WTF_ARRAY_LENGTH(stateFunctions) == static_cast<int>(SQLTransactionState::NumberOfStates)); |
| ASSERT(state < SQLTransactionState::NumberOfStates); |
| |
| return stateFunctions[static_cast<int>(state)]; |
| } |
| |
| void SQLTransactionBackend::computeNextStateAndCleanupIfNeeded() |
| { |
| // Only honor the requested state transition if we're not supposed to be |
| // cleaning up and shutting down: |
| if (m_frontend.m_database->opened()) { |
| setStateToRequestedState(); |
| ASSERT(m_nextState == SQLTransactionState::AcquireLock |
| || m_nextState == SQLTransactionState::OpenTransactionAndPreflight |
| || m_nextState == SQLTransactionState::RunStatements |
| || m_nextState == SQLTransactionState::PostflightAndCommit |
| || m_nextState == SQLTransactionState::CleanupAndTerminate |
| || m_nextState == SQLTransactionState::CleanupAfterTransactionErrorCallback); |
| |
| LOG(StorageAPI, "State %s\n", nameForSQLTransactionState(m_nextState)); |
| return; |
| } |
| |
| // If we get here, then we should be shutting down. Do clean up if needed: |
| if (m_nextState == SQLTransactionState::End) |
| return; |
| m_nextState = SQLTransactionState::End; |
| |
| // If the database was stopped, don't do anything and cancel queued work |
| LOG(StorageAPI, "Database was stopped or interrupted - cancelling work for this transaction"); |
| |
| // The current SQLite transaction should be stopped, as well |
| if (m_frontend.m_sqliteTransaction) { |
| m_frontend.m_sqliteTransaction->stop(); |
| m_frontend.m_sqliteTransaction = nullptr; |
| } |
| |
| // Terminate the frontend state machine. This also gets the frontend to |
| // call computeNextStateAndCleanupIfNeeded() and clear its wrappers |
| // if needed. |
| m_frontend.requestTransitToState(SQLTransactionState::End); |
| |
| // Redirect to the end state to abort, clean up, and end the transaction. |
| doCleanup(); |
| } |
| |
| void SQLTransactionBackend::notifyDatabaseThreadIsShuttingDown() |
| { |
| ASSERT(m_frontend.database().databaseThread().getThread() == &Thread::current()); |
| |
| // If the transaction is in progress, we should roll it back here, since this |
| // is our last opportunity to do something related to this transaction on the |
| // DB thread. Amongst other work, doCleanup() will clear m_sqliteTransaction |
| // which invokes SQLiteTransaction's destructor, which will do the roll back |
| // if necessary. |
| doCleanup(); |
| } |
| |
| void SQLTransactionBackend::acquireLock() |
| { |
| m_frontend.acquireLock(); |
| } |
| |
| void SQLTransactionBackend::openTransactionAndPreflight() |
| { |
| m_frontend.openTransactionAndPreflight(); |
| } |
| |
| void SQLTransactionBackend::runStatements() |
| { |
| m_frontend.runStatements(); |
| } |
| |
| void SQLTransactionBackend::cleanupAndTerminate() |
| { |
| m_frontend.cleanupAndTerminate(); |
| } |
| |
| void SQLTransactionBackend::cleanupAfterTransactionErrorCallback() |
| { |
| m_frontend.cleanupAfterTransactionErrorCallback(); |
| } |
| |
| // requestTransitToState() can be called from the frontend. Hence, it should |
| // NOT be modifying SQLTransactionBackend in general. The only safe field to |
| // modify is m_requestedState which is meant for this purpose. |
| void SQLTransactionBackend::requestTransitToState(SQLTransactionState nextState) |
| { |
| LOG(StorageAPI, "Scheduling %s for transaction %p\n", nameForSQLTransactionState(nextState), this); |
| m_requestedState = nextState; |
| ASSERT(m_requestedState != SQLTransactionState::End); |
| m_frontend.m_database->scheduleTransactionStep(m_frontend); |
| } |
| |
| // This state function is used as a stub function to plug unimplemented states |
| // in the state dispatch table. They are unimplemented because they should |
| // never be reached in the course of correct execution. |
| void SQLTransactionBackend::unreachableState() |
| { |
| ASSERT_NOT_REACHED(); |
| } |
| |
| } // namespace WebCore |
