org.apache.flume.channel

Class ChannelUtils

java.lang.Object

org.apache.flume.channel.ChannelUtils

public class ChannelUtils
extends Object

A collection of utilities for interacting with Channel objects. Use of these utilities prevents error-prone replication of required transaction usage semantics, and allows for more concise code.

However, as a side-effect of its generality, and in particular of its use of Callable, any checked exceptions thrown by user-created transactors will be silently wrapped with ChannelException before being propagated. Only direct use of transact(Channel,Callable) suffers from this issue, even though all other methods are based upon it, because none of the other methods are capable of producing or allowing checked exceptions in the first place.

Method Summary

Methods

Modifier and Type	Method and Description
static void	put(Channel channel, Collection<Event> events) A convenience method for multiple-event put transactions.
static void	put(Channel channel, Event event) A convenience method for single-event put transactions.
static Event	take(Channel channel) A convenience method for single-event take transactions.
static List<Event>	take(Channel channel, int max) A convenience method for multiple-event take transactions.
static <T> T	transact(Channel channel, Callable<T> transactor) A general optimistic implementation of Transaction client semantics.
static void	transact(Channel channel, Runnable transactor) A convenience method for transactions that don't require a return value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

put

public static void put(Channel channel,
       Event event)
                throws ChannelException

A convenience method for single-event put transactions.

Throws:

ChannelException

See Also:

transact(Channel,Callable)

put

public static void put(Channel channel,
       Collection<Event> events)
                throws ChannelException

A convenience method for multiple-event put transactions.

Throws:

ChannelException

See Also:

transact(Channel,Callable)

take

public static Event take(Channel channel)
                  throws ChannelException

A convenience method for single-event take transactions.

Returns:

a single event, or null if the channel has none available

Throws:

ChannelException

See Also:

transact(Channel,Callable)

take

public static List<Event> take(Channel channel,
               int max)
                        throws ChannelException

A convenience method for multiple-event take transactions.

Returns:

a list of at most max events

Throws:

ChannelException

See Also:

transact(Channel,Callable)

transact

public static void transact(Channel channel,
            Runnable transactor)
                     throws ChannelException

A convenience method for transactions that don't require a return value. Simply wraps the transactor using Executors.callable(java.lang.Runnable, T) and passes that to transact(Channel,Callable).

Throws:

ChannelException

See Also:

transact(Channel,Callable), Executors.callable(Runnable)

transact

public static <T> T transact(Channel channel,
             Callable<T> transactor)
                  throws ChannelException

A general optimistic implementation of Transaction client semantics. It gets a new transaction object from the channel, calls begin() on it, and then invokes the supplied transactor object. If an exception is thrown, then the transaction is rolled back; otherwise the transaction is committed and the value returned by the transactor is returned. In either case, the transaction is closed before the function exits. All secondary exceptions (i.e. those thrown by Transaction.rollback() or Transaction.close() while recovering from an earlier exception) are logged, allowing the original exception to be propagated instead.

This implementation is optimistic in that it expects transaction rollback to be infrequent: it will rollback a transaction only when the supplied transactor throws an exception, and exceptions are a fairly heavyweight mechanism for handling frequently-occurring events.

Returns:

the value returned by transactor.call()

Throws:

ChannelException