Package com.google.gerrit.server.git

Class MultiProgressMonitor

  • All Implemented Interfaces:
    com.google.gerrit.server.cancellation.RequestStateProvider
    public class MultiProgressMonitor
extends Object
implements com.google.gerrit.server.cancellation.RequestStateProvider
    Progress reporting interface that multiplexes multiple sub-tasks.

    Output is of the format: 

       Task: subA: 1, subB: 75% (3/4) (-)\r
   Task: subA: 2, subB: 75% (3/4), subC: 1 (\)\r
   Task: subA: 2, subB: 100% (4/4), subC: 1 (|)\r
   Task: subA: 4, subB: 100% (4/4), subC: 4, done    \n

    Callers should try to keep task and sub-task descriptions short, since the output should fit on one terminal line. (Note that git clients do not accept terminal control characters, so true multi-line progress messages would be impossible.)

    Whether the client is disconnected or the deadline is exceeded can be checked by checkIfCancelled(RequestStateProvider.OnCancelled). This allows the worker thread to react to cancellations and abort its execution and finish gracefully. After a cancellation has been signaled the worker thread has 10 * maxIntervalNanos to react to the cancellation and finish gracefully. If the worker thread doesn't finish gracefully in time after the cancellation has been signaled, the future executing the task is forcefully cancelled which means that the worker thread gets interrupted and an internal error is returned to the client. To react to cancellations it is recommended that the task opens a RequestStateContext in a try-with-resources block to register the MultiProgressMonitor as a RequestStateProvider. This way the worker thread gets aborted by a RequestCancelledException when the request is cancelled which allows the worker thread to handle the cancellation gracefully by catching this exception (e.g. to return a proper error message). RequestCancelledException is only thrown when the worker thread checks for cancellation via RequestStateContext.abortIfCancelled(). E.g. this is done whenever TraceContext.TraceTimer is opened/closed.

    • Field Detail

      • UNKNOWN

        public static final int UNKNOWN
        Constant indicating the total work units cannot be predicted.
        See Also:
        Constant Field Values

    • Method Detail

      • waitFor

        public <T> T waitFor​(Future<T> workerFuture,
                     long taskTimeoutTime,
                     TimeUnit taskTimeoutUnit,
                     long cancellationTimeoutTime,
                     TimeUnit cancellationTimeoutUnit)
              throws TimeoutException
        Wait for a task managed by a Future.

        Must be called from the main thread, not a worker thread. Once a worker thread calls end(), the future has an additional maxInterval to finish before it is forcefully cancelled and ExecutionException is thrown.

        Parameters:
        workerFuture - a future that returns when worker threads are finished.
        taskTimeoutTime - overall timeout for the task; the future gets a cancellation signal after this timeout is exceeded; non-positive values indicate no timeout.
        taskTimeoutUnit - unit for overall task timeout.
        cancellationTimeoutTime - timeout for the task to react to the cancellation signal; if the task doesn't terminate within this time it is forcefully cancelled; non-positive values indicate no timeout.
        cancellationTimeoutUnit - unit for the cancellation timeout.
        Throws:
        TimeoutException - if this thread or a worker thread was interrupted, the worker was cancelled, or timed out waiting for a worker to call end().

      • beginSubTask

        public MultiProgressMonitor.Task beginSubTask​(String subTask,
                                              int subTaskWork)
        Begin a sub-task.
        Parameters:
        subTask - sub-task name.
        subTaskWork - total work units in sub-task, or UNKNOWN.
        Returns:
        sub-task handle.

      • end

        public void end()
        End the overall task.

        Must be called from a worker thread.

      • checkIfCancelled

        public void checkIfCancelled​(com.google.gerrit.server.cancellation.RequestStateProvider.OnCancelled onCancelled)
        Specified by:
        checkIfCancelled in interface com.google.gerrit.server.cancellation.RequestStateProvider