/// <summary>
/// Computes a result, or throws an exception if unable to do so.
/// </summary>
/// <returns></returns>
public T Call()
{
try
{
WaitForStartSignal();
log.DebugFormat("Starting execution of {0} against shard {1}", operation.OperationName, shard);
///If addResult() returns true it means there is no more work to be
///performed. Cancel all the outstanding tasks.
if (exitStrategy.AddResult(operation.Execute(shard), shard))
{
log.DebugFormat("Short-circuiting execution of {0} on other threads after execution against shard {1}",
operation.OperationName, shard);
//It's ok to cancel ourselves because StartAwareFutureTask.cancel()
//will return false if a task has already started executing, and we're
//already executing.
log.DebugFormat("Checking {0} future tasks to see if they need to be cancelled.", futureTasks.Count);
foreach (StartAwareFutureTask <T> ft in futureTasks)
{
log.DebugFormat("Preparing to cancel future task %d.", ft.Id);
//If a task was successfully cancelled that means it had not yet
//started running. Since the task won't run, the task won't be
// able to decrement the CountDownLatch. We need to decrement
//it on behalf of the cancelled task.
if (ft.Cancel(INTERRUPT_IF_RUNNING))
{
log.Debug("Task cancel returned true, decrementing counter on its behalf.");
doneSignal.CountDown();
}
else
{
log.Debug("Task cancel returned false, not decrementing counter on its behalf.");
}
}
}
else
{
log.DebugFormat("No need to short-cirtcuit execution of {0} on other threads after execution against shard {1}",
operation.OperationName, shard);
}
}
finally
{
// counter must get decremented no matter what
log.DebugFormat("Decrementing counter for operation {0} on shard {1}", operation.OperationName, shard);
doneSignal.CountDown();
}
return(default(T));
}
public T Apply <T>(IList <IShard> shards, IShardOperation <T> operation, IExitStrategy <T> exitStrategy,
IExitOperationsCollector exitOperationsCollector)
{
foreach (IShard shard in GetNextOrderingOfShards(shards))
{
if (exitStrategy.AddResult(operation.Execute(shard), shard))
{
log.DebugFormat("Short-circuiting operation {0} after execution against shard {1}",
operation.OperationName, shard);
break;
}
}
return(exitStrategy.CompileResults(exitOperationsCollector));
}