Queue (Google App Engine API for Java)

com.google.appengine.api.taskqueue

Interface Queue


  • public interface Queue
    Queue is used to manage a task queue.

    Implementations of this interface must be threadsafe.

    Queues are transactional. If a datastore transaction is in progress when add() or add(TaskOptions) is invoked, the task will only be added to the queue if the datastore transaction successfully commits. If you want to add a task to a queue and have that operation succeed or fail independently of an existing datastore transaction you can invoke add(Transaction, TaskOptions) with a null transaction argument. Note that while the addition of the task to the queue can participate in an existing transaction, the execution of the task cannot participate in this transaction. In other words, when the transaction commits you are guaranteed that your task will be added and run, not that your task executed successfully.

    Queues may be configured in either push or pull mode, but they share the same interface. However, only tasks with TaskOptions.Method.PULL may be added to pull queues. The tasks in push queues must be added with one of the other available methods.

    Pull mode queues do not automatically deliver tasks to the application. The application is required to call leaseTasks to acquire a lease on the task and process them explicitly. Attempting to call leaseTasks on a push queue causes a InvalidQueueModeException to be thrown. When the task processing has finished processing a task that is leased, it should call deleteTask(String). If deleteTask is not called before the lease expires, the task will again be available for lease.

    Queue mode can be switched between push and pull. When switching from push to pull, tasks will stay in the task queue and are available for lease, but url and headers information will be ignored when returning the tasks. When switching from pull to push, existing tasks will remain in the queue but will fail on auto-execution because they lack a url. If the queue mode is once again changed to pull, these tasks will eventually be available for lease.

    • Field Summary

      Fields 
      Modifier and Type Field and Description
      static java.lang.String DEFAULT_QUEUE
      The default queue name.
      static java.lang.String DEFAULT_QUEUE_PATH
      The default queue path.

    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method and Description
      TaskHandle add()
      Submits a task to this queue with an auto generated name with default options.
      java.util.List<TaskHandle> add(java.lang.Iterable<TaskOptions> taskOptions)
      Submits tasks to this queue.
      TaskHandle add(TaskOptions taskOptions)
      Submits a task to this queue.
      java.util.List<TaskHandle> add(Transaction txn, java.lang.Iterable<TaskOptions> taskOptions)
      Submits tasks to this queue in the provided Transaction.
      TaskHandle add(Transaction txn, TaskOptions taskOptions)
      Submits a task to this queue in the provided Transaction.
      java.util.concurrent.Future<TaskHandle> addAsync()
      Asynchronously submits a task to this queue with an auto generated name with default options.
      java.util.concurrent.Future<java.util.List<TaskHandle>> addAsync(java.lang.Iterable<TaskOptions> taskOptions)
      Asynchronously submits tasks to this queue.
      java.util.concurrent.Future<TaskHandle> addAsync(TaskOptions taskOptions)
      Asynchronously submits a task to this queue.
      java.util.concurrent.Future<java.util.List<TaskHandle>> addAsync(Transaction txn, java.lang.Iterable<TaskOptions> taskOptions)
      Asynchronously submits tasks to this queue in the provided Transaction.
      java.util.concurrent.Future<TaskHandle> addAsync(Transaction txn, TaskOptions taskOptions)
      Asynchronously submits a task to this queue in the provided Transaction.
      java.util.List<java.lang.Boolean> deleteTask(java.util.List<TaskHandle> taskHandles)
      Deletes a list of tasks from this Queue.
      boolean deleteTask(java.lang.String taskName)
      Deletes a task from this Queue.
      boolean deleteTask(TaskHandle taskHandle)
      Deletes a task from this Queue.
      java.util.concurrent.Future<java.util.List<java.lang.Boolean>> deleteTaskAsync(java.util.List<TaskHandle> taskHandles)
      Asynchronously deletes a list of tasks from this Queue.
      java.util.concurrent.Future<java.lang.Boolean> deleteTaskAsync(java.lang.String taskName)
      Asynchronously deletes a task from this Queue.
      java.util.concurrent.Future<java.lang.Boolean> deleteTaskAsync(TaskHandle taskHandle)
      Asynchronously deletes a task from this Queue.
      QueueStatistics fetchStatistics()
      Obtain statistics for this Queue.
      java.util.concurrent.Future<QueueStatistics> fetchStatisticsAsync(java.lang.Double deadlineInSeconds)
      Asynchronously obtains statistics for this Queue.
      java.lang.String getQueueName()
      Returns the queue name.
      java.util.List<TaskHandle> leaseTasks(LeaseOptions options)
      Leases tasks from this queue, with lease period and other options specified by options.
      java.util.List<TaskHandle> leaseTasks(long lease, java.util.concurrent.TimeUnit unit, long countLimit)
      Leases up to countLimit tasks from this queue for a period specified by lease and unit.
      java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksAsync(LeaseOptions options)
      Asynchronously leases tasks from this queue, with lease period and other options specified by options.
      java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksAsync(long lease, java.util.concurrent.TimeUnit unit, long countLimit)
      Asynchronously leases up to countLimit tasks from this queue for a period specified by lease and unit.
      java.util.List<TaskHandle> leaseTasksByTag(long lease, java.util.concurrent.TimeUnit unit, long countLimit, java.lang.String tag)
      Leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag.
      java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksByTagAsync(long lease, java.util.concurrent.TimeUnit unit, long countLimit, java.lang.String tag)
      Asynchronously leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag.
      java.util.List<TaskHandle> leaseTasksByTagBytes(long lease, java.util.concurrent.TimeUnit unit, long countLimit, byte[] tag)
      Leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag.
      java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksByTagBytesAsync(long lease, java.util.concurrent.TimeUnit unit, long countLimit, byte[] tag)
      Asynchronously leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag.
      TaskHandle modifyTaskLease(TaskHandle taskHandle, long lease, java.util.concurrent.TimeUnit unit)
      Modify the lease of the specified task in this Queue for a period of time specified by lease and unit.
      void purge()
      Clears all the tasks in this Queue.

    • Field Detail

      • DEFAULT_QUEUE

        static final java.lang.String DEFAULT_QUEUE
        The default queue name.
        See Also:
        Constant Field Values

      • DEFAULT_QUEUE_PATH

        static final java.lang.String DEFAULT_QUEUE_PATH
        The default queue path.
        See Also:
        Constant Field Values

    • Method Detail

      • getQueueName

        java.lang.String getQueueName()
        Returns the queue name.

      • add

        java.util.List<TaskHandle> add(java.lang.Iterable<TaskOptions> taskOptions)
        Submits tasks to this queue.

        Submission is not atomic i.e. if this method throws then some tasks may have been added to the queue.

        Parameters:
        taskOptions - An iterable over task definitions.
        Returns:
        A list containing a TaskHandle for each added task.
        Throws:
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        TaskAlreadyExistsException - If any of the provided TaskOptions contained a name of a task that was previously created, and if no other Exception would be thrown. Note that if a TaskAlreadyExistsException is caught, the caller can be guaranteed that for each one of the provided TaskOptions, either the corresponding task was successfully added, or a task with the given name was successfully added in the past.
        TransientFailureException - Attempting the request after this exception may succeed.
        UnsupportedTranslationException - If chosen character encoding is unsupported.
        InvalidQueueModeException - task method is TaskOptions.Method.PULL and queue is push queue or vice versa.

      • addAsync

        java.util.concurrent.Future<TaskHandle> addAsync(TaskOptions taskOptions)
        Asynchronously submits a task to this queue.
        Parameters:
        taskOptions - The definition of the task.
        Returns:
        A Future with a result type of TaskHandle.
        Throws:
        UnsupportedTranslationException - If chosen character encoding is unsupported.

      • addAsync

        java.util.concurrent.Future<java.util.List<TaskHandle>> addAsync(java.lang.Iterable<TaskOptions> taskOptions)
        Asynchronously submits tasks to this queue.

        Submission is not atomic i.e. if this method fails then some tasks may have been added to the queue.

        Parameters:
        taskOptions - An iterable over task definitions.
        Returns:
        A Future whose result is a list containing a TaskHandle for each added task.
        Throws:
        UnsupportedTranslationException - If chosen character encoding is unsupported.

      • addAsync

        java.util.concurrent.Future<TaskHandle> addAsync(Transaction txn,
                                                 TaskOptions taskOptions)
        Asynchronously submits a task to this queue in the provided Transaction.

        A task is added if and only if the transaction is applied successfully.

        Parameters:
        txn - an enclosing Transaction or null, if not null a task cannot be named.
        taskOptions - The definition of the task.
        Returns:
        A Future with a result type of TaskHandle.
        Throws:
        UnsupportedTranslationException - If chosen character encoding is unsupported.

      • addAsync

        java.util.concurrent.Future<java.util.List<TaskHandle>> addAsync(Transaction txn,
                                                                 java.lang.Iterable<TaskOptions> taskOptions)
        Asynchronously submits tasks to this queue in the provided Transaction.

        The tasks are added if and only if the transaction is applied successfully.

        Parameters:
        txn - an enclosing Transaction or null, if not null a task cannot be named.
        taskOptions - An iterable over task definitions.
        Returns:
        A Future whose result is a list containing a TaskHandle for each added task.
        Throws:
        UnsupportedTranslationException - If chosen character encoding is unsupported.

      • deleteTask

        boolean deleteTask(java.lang.String taskName)
        Deletes a task from this Queue. Task is identified by taskName.
        Parameters:
        taskName - name of the task to delete.
        Returns:
        True if the task was successfully deleted. False if the task was not found or was previously deleted.
        Throws:
        java.lang.IllegalArgumentException - if the provided name is null, empty or doesn't match the expected pattern.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        TransientFailureException - Attempting the request after this exception may succeed.

      • deleteTask

        boolean deleteTask(TaskHandle taskHandle)
        Deletes a task from this Queue. Task is identified by a TaskHandle.
        Parameters:
        taskHandle - handle of the task to delete.
        Returns:
        True if the task was successfully deleted. False if the task was not found or was previously deleted.
        Throws:
        java.lang.IllegalArgumentException - if the provided name is null, empty or doesn't match the expected pattern.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        QueueNameMismatchException - if the task handle refers to a different named queue.
        TransientFailureException - Attempting the request after this exception may succeed.

      • deleteTask

        java.util.List<java.lang.Boolean> deleteTask(java.util.List<TaskHandle> taskHandles)
        Deletes a list of tasks from this Queue. The tasks are identified by a list of TaskHandles. This method supports deleting up to 1000 tasks.
        Parameters:
        taskHandles - list of handles of tasks to delete.
        Returns:
        List<Boolean> that represents the result of deleting each task in the same order as the input handles. True if a task was successfully deleted. False if the task was not found or was previously deleted.
        Throws:
        java.lang.IllegalArgumentException - if the provided name is null, empty or doesn't match the expected pattern, or if the size of taskHandles is too large.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        QueueNameMismatchException - if the task handle refers to a different named queue.
        TransientFailureException - Attempting the request after this exception may succeed.

      • deleteTaskAsync

        java.util.concurrent.Future<java.lang.Boolean> deleteTaskAsync(java.lang.String taskName)
        Asynchronously deletes a task from this Queue. Task is identified by taskName.
        Parameters:
        taskName - name of the task to delete.
        Returns:
        A Future whose result is True if the task was successfully deleted, False if the task was not found or was previously deleted.
        Throws:
        java.lang.IllegalArgumentException - if the provided name is null, empty or doesn't match the expected pattern.

      • deleteTaskAsync

        java.util.concurrent.Future<java.lang.Boolean> deleteTaskAsync(TaskHandle taskHandle)
        Asynchronously deletes a task from this Queue. Task is identified by a TaskHandle.
        Parameters:
        taskHandle - handle of the task to delete.
        Returns:
        A Future whose result is True if the task was successfully deleted, False if the task was not found or was previously deleted.
        Throws:
        java.lang.IllegalArgumentException - if the provided name is null, empty or doesn't match the expected pattern.
        QueueNameMismatchException - if the task handle refers to a different named queue.

      • deleteTaskAsync

        java.util.concurrent.Future<java.util.List<java.lang.Boolean>> deleteTaskAsync(java.util.List<TaskHandle> taskHandles)
        Asynchronously deletes a list of tasks from this Queue. The tasks are identified by a list of TaskHandles. This method supports deleting up to 1000 tasks.
        Parameters:
        taskHandles - list of handles of tasks to delete.
        Returns:
        A Future whose result is a List<Boolean> that represents the result of deleting each task in the same order as the input handles. True if a task was successfully deleted. False if the task was not found or was previously deleted.
        Throws:
        java.lang.IllegalArgumentException - if the provided name is null, empty or doesn't match the expected pattern.
        QueueNameMismatchException - if the task handle refers to a different named queue.

      • leaseTasks

        java.util.List<TaskHandle> leaseTasks(long lease,
                                      java.util.concurrent.TimeUnit unit,
                                      long countLimit)
        Leases up to countLimit tasks from this queue for a period specified by lease and unit. If fewer tasks than countLimit are available, all available tasks in this Queue will be returned. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested. It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week. If you generate more than 10 LeaseTasks requests per second, only the first 10 requests will return results. The others will return no results.
        Parameters:
        lease - Number of units in the lease period
        unit - Time unit of the lease period
        countLimit - maximum number of tasks to lease
        Returns:
        A list of TaskHandle for each leased task.
        Throws:
        InvalidQueueModeException - if the target queue is not in pull mode.
        java.lang.IllegalArgumentException - if lease < 0, countLimit <= 0, or either is too large.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        TransientFailureException - Attempting the request after this exception may succeed.

      • leaseTasksByTagBytes

        java.util.List<TaskHandle> leaseTasksByTagBytes(long lease,
                                                java.util.concurrent.TimeUnit unit,
                                                long countLimit,
                                                byte[] tag)
        Leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag. If tag is null, tasks having the same tag as the task with earliest eta will be returned. If fewer such tasks than countLimit are available, all available such tasks in this Queue will be returned. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested. It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.
        Parameters:
        lease - Number of units in the lease period
        unit - Time unit of the lease period
        countLimit - maximum number of tasks to lease
        tag - User defined tag required for returned tasks. If null, the tag of the task with earliest eta will be used.
        Returns:
        A list of TaskHandle for each leased task.
        Throws:
        InvalidQueueModeException - if the target queue is not in pull mode.
        java.lang.IllegalArgumentException - if lease < 0, countLimit <= 0, or either is too large.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        TransientFailureException - Attempting the request after this exception may succeed.

      • leaseTasksByTag

        java.util.List<TaskHandle> leaseTasksByTag(long lease,
                                           java.util.concurrent.TimeUnit unit,
                                           long countLimit,
                                           java.lang.String tag)
        Leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag. If tag is null, tasks having the same tag as the task with earliest eta will be returned. If fewer such tasks than countLimit are available, all available such tasks in this Queue will be returned. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested.

        It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.

        Parameters:
        lease - Number of units in the lease period
        unit - Time unit of the lease period
        countLimit - maximum number of tasks to lease
        tag - User defined String tag required for returned tasks. If null, the tag of the task with earliest eta will be used.
        Returns:
        A list of TaskHandle for each leased task.
        Throws:
        InvalidQueueModeException - if the target queue is not in pull mode.
        java.lang.IllegalArgumentException - if lease < 0, countLimit <= 0, or either is too large.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        TransientFailureException - Attempting the request after this exception may succeed.

      • leaseTasks

        java.util.List<TaskHandle> leaseTasks(LeaseOptions options)
        Leases tasks from this queue, with lease period and other options specified by options. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested.

        If options specifies a tag, only tasks having that tag will be returned. If options specifies no tag, but does specify groupByTag, only tasks having the same tag as the task with earliest eta will be returned.

        It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.

        Parameters:
        options - Specific options for this lease request
        Returns:
        A list of TaskHandle for each leased task.
        Throws:
        InvalidQueueModeException - if the target queue is not in pull mode.
        java.lang.IllegalArgumentException - if lease period or countLimit is null or either is too large.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist. (see queue.xml)
        TransientFailureException - Attempting the request after this exception may succeed.

      • leaseTasksAsync

        java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksAsync(long lease,
                                                                        java.util.concurrent.TimeUnit unit,
                                                                        long countLimit)
        Asynchronously leases up to countLimit tasks from this queue for a period specified by lease and unit. If fewer tasks than countLimit are available, all available tasks in this Queue will be returned. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested. It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.
        Parameters:
        lease - Number of units in the lease period
        unit - Time unit of the lease period
        countLimit - maximum number of tasks to lease
        Returns:
        A Future whose result is a list of TaskHandle for each leased task.
        Throws:
        java.lang.IllegalArgumentException - if lease < 0, countLimit <= 0, or either is too large.

      • leaseTasksByTagBytesAsync

        java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksByTagBytesAsync(long lease,
                                                                                  java.util.concurrent.TimeUnit unit,
                                                                                  long countLimit,
                                                                                  byte[] tag)
        Asynchronously leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag. If tag is null, tasks having the same tag as the task with earliest eta will be returned. If fewer such tasks than countLimit are available, all available such tasks in this Queue will be returned. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested. It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.
        Parameters:
        lease - Number of units in the lease period
        unit - Time unit of the lease period
        countLimit - maximum number of tasks to lease
        tag - User defined tag required for returned tasks. If null, the tag of the task with earliest eta will be used.
        Returns:
        A Future whose result is a list of TaskHandle for each leased task.
        Throws:
        java.lang.IllegalArgumentException - if lease < 0, countLimit <= 0, or either is too large.

      • leaseTasksByTagAsync

        java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksByTagAsync(long lease,
                                                                             java.util.concurrent.TimeUnit unit,
                                                                             long countLimit,
                                                                             java.lang.String tag)
        Asynchronously leases up to countLimit tasks from this queue for a period specified by lease and unit, having tag tag. If tag is null, tasks having the same tag as the task with earliest eta will be returned. If fewer such tasks than countLimit are available, all available such tasks in this Queue will be returned. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested.

        It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.

        Parameters:
        lease - Number of units in the lease period
        unit - Time unit of the lease period
        countLimit - maximum number of tasks to lease
        tag - User defined String tag required for returned tasks. If null, the tag of the task with earliest eta will be used.
        Returns:
        A Future whose result is a list of TaskHandle for each leased task.
        Throws:
        java.lang.IllegalArgumentException - if lease < 0, countLimit <= 0, or either is too large.

      • leaseTasksAsync

        java.util.concurrent.Future<java.util.List<TaskHandle>> leaseTasksAsync(LeaseOptions options)
        Asynchronously leases tasks from this queue, with lease period and other options specified by options. The available tasks are those in the queue having the earliest eta such that eta is prior to the time at which the lease is requested.

        If options specifies a tag, only tasks having that tag will be returned. If options specifies no tag, but does specify groupByTag, only tasks having the same tag as the task with earliest eta will be returned.

        It is guaranteed that the leased tasks will be unavailable for lease to others in the lease period. You must call deleteTask to prevent the task from being leased again after the lease period. This method supports leasing a maximum of 1000 tasks for no more than one week.

        Parameters:
        options - Specific options for this lease request
        Returns:
        A Future whose result is a list of TaskHandle for each leased task.
        Throws:
        java.lang.IllegalArgumentException - if lease period or countLimit is null or either is too large.

      • purge

        void purge()
        Clears all the tasks in this Queue. This function returns immediately. Some delay may apply on the server before the Queue is actually purged. Tasks being executed at the time the purge call is made will continue executing, other tasks in this Queue will continue being dispatched and executed before the purge call takes effect.
        Throws:
        java.lang.IllegalStateException - If the Queue does not exist. (see queue.xml)
        TransientFailureException - Attempting the request after this exception may succeed.
        InternalFailureException

      • modifyTaskLease

        TaskHandle modifyTaskLease(TaskHandle taskHandle,
                           long lease,
                           java.util.concurrent.TimeUnit unit)
        Modify the lease of the specified task in this Queue for a period of time specified by lease and unit. A lease time of 0 will relinquish the lease on the task and make it available to be leased by calling leaseTasks.
        Parameters:
        taskHandle - handle of the task that is having its lease modified.
        lease - Number of units in the lease period.
        unit - Time unit of the lease period.
        Returns:
        Updated TaskHandle with the new lease period.
        Throws:
        InvalidQueueModeException - if the target queue is not in pull mode.
        java.lang.IllegalArgumentException - if lease < 0 or too large.
        InternalFailureException
        java.lang.IllegalStateException - If the queue does not exist, or the task lease has expired or the queue has been paused.
        TransientFailureException - Attempting the request after this exception may succeed.

      • fetchStatisticsAsync

        java.util.concurrent.Future<QueueStatistics> fetchStatisticsAsync(java.lang.Double deadlineInSeconds)
        Asynchronously obtains statistics for this Queue.
        Parameters:
        deadlineInSeconds - the maximum duration, in seconds, that the fetch statistics request can run. A default deadline will be used if null is supplied.
        Returns:
        A Future with a result type of QueueStatistics.
        Throws:
        java.lang.IllegalArgumentException - if deadlineInSeconds <= 0.