com::sleepycat::collections::TransactionRunner Class Reference

Public Member Functions
	TransactionRunner (Environment env)
	TransactionRunner (Environment env, int maxRetries, TransactionConfig config)
int	getMaxRetries ()
void	setMaxRetries (int maxRetries)
boolean	getAllowNestedTransactions ()
void	setAllowNestedTransactions (boolean allowNestedTxn)
TransactionConfig	getTransactionConfig ()
void	setTransactionConfig (TransactionConfig config)
void	run (TransactionWorker worker) throws DatabaseException, Exception
Static Public Attributes
static final int	DEFAULT_MAX_RETRIES = 10

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Detailed Description

Starts a transaction, calls TransactionWorker#doWork, and handles transaction retry and exceptions. To perform a transaction, the user implements the TransactionWorker interface and passes an instance of that class to the run method.

A single TransactionRunner instance may be used by any number of threads for any number of transactions.

The behavior of the run() method depends on whether the environment is transactional, whether nested transactions are enabled, and whether a transaction is already active.

• When the run() method is called in a transactional environment and no transaction is active for the current thread, a new transaction is started before calling doWork(). If DeadlockException is thrown by doWork(), the transaction will be aborted and the process will be repeated up to the maximum number of retries. If another exception is thrown by doWork() or the maximum number of retries has occurred, the transaction will be aborted and the exception will be rethrown by the run() method. If no exception is thrown by doWork(), the transaction will be committed. The run() method will not attempt to commit or abort a transaction if it has already been committed or aborted by doWork().

• When the run() method is called and a transaction is active for the current thread, and nested transactions are enabled, a nested transaction is started before calling doWork(). The transaction that is active when calling the run() method will become the parent of the nested transaction. The nested transaction will be committed or aborted by the run() method following the same rules described above. Note that nested transactions may not be enabled for the JE product, since JE does not support nested transactions.

• When the run() method is called in a non-transactional environment, the doWork() method is called without starting a transaction. The run() method will return without committing or aborting a transaction, and any exceptions thrown by the doWork() method will be thrown by the run() method.

• When the run() method is called and a transaction is active for the current thread and nested transactions are not enabled (the default) the same rules as above apply. All the operations performed by the doWork() method will be part of the currently active transaction.

In a transactional environment, the rules described above support nested calls to the run() method and guarantee that the outermost call will cause the transaction to be committed or aborted. This is true whether or not nested transactions are supported or enabled. Note that nested transactions are provided as an optimization for improving concurrency but do not change the meaning of the outermost transaction. Nested transactions are not currently supported by the JE product.

Author:

Mark Hayes

Definition at line 75 of file TransactionRunner.java.

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Constructor & Destructor Documentation

com::sleepycat::collections::TransactionRunner::TransactionRunner (  Environment  env  )  [inline]

Creates a transaction runner for a given Berkeley DB environment. The default maximum number of retries (DEFAULT_MAX_RETRIES) and a null (default) TransactionConfig will be used. Parameters: env  is the environment for running transactions. Definition at line 93 of file TransactionRunner.java. References DEFAULT_MAX_RETRIES.

com::sleepycat::collections::TransactionRunner::TransactionRunner (  Environment  env, int  maxRetries, TransactionConfig  config )  [inline]

Creates a transaction runner for a given Berkeley DB environment and with a given number of maximum retries. Parameters: env  is the environment for running transactions. maxRetries  is the maximum number of retries that will be performed when deadlocks are detected. config  the transaction configuration used for calling Environment#beginTransaction, or null to use the default configuration. The configuration object is not cloned, and any modifications to it will impact subsequent transactions. Definition at line 112 of file TransactionRunner.java.

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Member Function Documentation

boolean com::sleepycat::collections::TransactionRunner::getAllowNestedTransactions (   )  [inline]

Returns whether nested transactions will be created if run() is called when a transaction is already active for the current thread. By default this property is false. Note that this method always returns false in the JE product, since nested transactions are not supported by JE. Definition at line 149 of file TransactionRunner.java.

int com::sleepycat::collections::TransactionRunner::getMaxRetries (   )  [inline]

Returns the maximum number of retries that will be performed when deadlocks are detected. Definition at line 125 of file TransactionRunner.java.

TransactionConfig com::sleepycat::collections::TransactionRunner::getTransactionConfig (   )  [inline]

Returns the transaction configuration used for calling Environment#beginTransaction. If this property is null, the default configuration is used. The configuration object is not cloned, and any modifications to it will impact subsequent transactions. Returns: the transaction configuration. Definition at line 182 of file TransactionRunner.java.

void com::sleepycat::collections::TransactionRunner::run (  TransactionWorker  worker  )  throws DatabaseException, Exception [inline]

Calls the TransactionWorker#doWork method and, for transactional environments, may begin and end a transaction. If the environment given is non-transactional, a transaction will not be used but the doWork() method will still be called. See the class description for more information. Exceptions: DeadlockException  when it is thrown by doWork() and the maximum number of retries has occurred. The transaction will have been aborted by this method. Exception  when any other exception is thrown by doWork(). The exception will first be unwrapped by calling ExceptionUnwrapper#unwrap. The transaction will have been aborted by this method. Definition at line 218 of file TransactionRunner.java. References com::sleepycat::collections::CurrentTransaction::abortTransaction(), com::sleepycat::collections::CurrentTransaction::beginTransaction(), com::sleepycat::collections::CurrentTransaction::commitTransaction(), and com::sleepycat::collections::CurrentTransaction::getTransaction(). Referenced by collections::hello::HelloDatabaseWorld::main(), and collections::access::AccessExample::run().

void com::sleepycat::collections::TransactionRunner::setAllowNestedTransactions (  boolean  allowNestedTxn  )  [inline]

Changes whether nested transactions will be created if run() is called when a transaction is already active for the current thread. Calling this method does not impact transactions already running. Note that true may not be passed to this method in the JE product, since nested transactions are not supported by JE. Definition at line 163 of file TransactionRunner.java.

void com::sleepycat::collections::TransactionRunner::setMaxRetries (  int  maxRetries  )  [inline]

Changes the maximum number of retries that will be performed when deadlocks are detected. Calling this method does not impact transactions already running. Definition at line 135 of file TransactionRunner.java.

void com::sleepycat::collections::TransactionRunner::setTransactionConfig (  TransactionConfig  config  )  [inline]

Changes the transaction configuration used for calling Environment#beginTransaction. If this property is null, the default configuration is used. The configuration object is not cloned, and any modifications to it will impact subsequent transactions. Parameters: config  the transaction configuration. Definition at line 197 of file TransactionRunner.java.

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Field Documentation

final int com::sleepycat::collections::TransactionRunner::DEFAULT_MAX_RETRIES = 10 [static]

The default maximum number of retries. Definition at line 78 of file TransactionRunner.java. Referenced by TransactionRunner().

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The documentation for this class was generated from the following file:

• /home/huihoo/src/db/db-4.4.16/java/src/com/sleepycat/collections/TransactionRunner.java

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