Task 1

The Task class represents a single operation that returns a value and that usually executes asynchronously. Task objects are one of the central components of the task-based asynchronous pattern first introduced in the .NET Framework 4. Because the work performed by a Task object typically executes asynchronously on a thread pool thread rather than synchronously on the main application thread, you can use the Status property, as well as the IsCanceled, IsCompleted, and IsFaulted properties, to determine the state of a task. Most commonly, a lambda expression is used to specify the work that the task is to perform.

Task instances may be created in a variety of ways. The most common approach, which is available starting with the .NET Framework 4.5, is to call the static Task.Run(Func) or Task.Run(Func, CancellationToken) method. These methods provide a simple way to start a task by using default values and without acquiring additional parameters. The following example uses the Task.Run(Func) method to start a task that loops and then displays the number of loop iterations:

Task 1

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An alternative, and the most common way to start a task in the .NET Framework 4, is to call the static TaskFactory.StartNew or TaskFactory.StartNew method. The Task.Factory property returns a TaskFactory object, and the Task.Factory property returns a TaskFactory object. Overloads of their StartNew method let you pass arguments, define task creation options, and specify a task scheduler. The following example uses the TaskFactory.StartNew(Func) method to start a task. It is functionally equivalent to the code in the previous example.

The Task class also provides constructors that initialize the task but that do not schedule it for execution. For performance reasons, the Task.Run and Task.Factory.StartNew methods are the preferred mechanisms for creating and scheduling computational tasks, but for scenarios where task creation and scheduling must be separated, the constructors may be used, and the task's Start method may then be used to schedule the task for execution at a later time.

Starting with desktop apps that target the .NET Framework 4.6, the culture of the thread that creates and invokes a task becomes part of the thread's context. That is, regardless of the current culture of the thread on which the task executes, the current culture of the task is the culture of the calling thread. For apps that target versions of the .NET Framework prior to the .NET Framework 4.6, the culture of the task is the culture of the thread on which the task executes. For more information, see the "Culture and task-based asynchronous operations" section in the CultureInfo topic. Note that Store apps follow the Windows Runtime in setting and getting the default culture.

For operations that do not return a value, you use the Task class. Starting with C# 7.0, for a more lightweight task that is a value type rather than a reference type, use the System.Threading.Tasks.ValueTask structure.

Creates a continuation that executes based on the specified task continuation options when the target Task completes and returns a value. The continuation receives caller-supplied state information and a cancellation token and uses the specified scheduler.

The async with statement will wait for all tasks in the group to finish.While waiting, new tasks may still be added to the group(for example, by passing tg into one of the coroutinesand calling tg.create_task() in that coroutine).Once the last task has finished and the async with block is exited,no new tasks may be added to the group.

Once all tasks have finished, if any tasks have failedwith an exception other than asyncio.CancelledError,those exceptions are combined in anExceptionGroup or BaseExceptionGroup(as appropriate; see their documentation)which is then raised.

Two base exceptions are treated specially:If any task fails with KeyboardInterrupt or SystemExit,the task group still cancels the remaining tasks and waits for them,but then the initial KeyboardInterrupt or SystemExitis re-raised instead of ExceptionGroup or BaseExceptionGroup.

If the body of the async with statement exits with an exception(so __aexit__() is called with an exception set),this is treated the same as if one of the tasks failed:the remaining tasks are cancelled and then waited for,and non-cancellation exceptions are grouped into anexception group and raised.The exception passed into __aexit__(),unless it is asyncio.CancelledError,is also included in the exception group.The same special case is made forKeyboardInterrupt and SystemExit as in the previous paragraph.

A new alternative to create and run tasks concurrently andwait for their completion is asyncio.TaskGroup. TaskGroupprovides stronger safety guarantees than gather for scheduling a nesting of subtasks:if a task (or a subtask, a task scheduled by a task)raises an exception, TaskGroup will, while gather will not,cancel the remaining scheduled tasks).

When using this factory (via loop.set_task_factory(asyncio.eager_task_factory)),coroutines begin execution synchronously during Task construction.Tasks are only scheduled on the event loop if they block.This can be a performance improvement as the overhead of loop schedulingis avoided for coroutines that complete synchronously.

If long_running_task takes more than 10 seconds to complete,the context manager will cancel the current task and handlethe resulting asyncio.CancelledError internally, transforming itinto a TimeoutError which can be caught and handled.

An optional keyword-only eager_start argument allows eagerly startingthe execution of the asyncio.Task at task creation time.If set to True and the event loop is running, the task will startexecuting the coroutine immediately, until the first time the coroutineblocks. If the coroutine returns or raises without blocking, the taskwill be finished eagerly and will skip scheduling to the event loop.

Note that if this number is greater than zero but the Task isstill executing, cancelled() will still return False.This is because this number can be lowered by calling uncancel(),which can lead to the task not being cancelled after all if thecancellation requests go down to zero.

Each task belongs to a Project. You can use the various methods on TaskContainer to create and lookup task instances. For example, TaskContainer.create(String) creates an empty task with the given name. You can also use thetask keyword in your build file:

Each task has a name, which can be used to refer to the task within its owning project, and a fully qualifiedpath, which is unique across all tasks in all projects. The path is the concatenation of the owning project's pathand the task's name. Path elements are separated using the ":"character.

A Task is made up of a sequence of Action objects. When the task is executed, each of theactions is executed in turn, by calling Action.execute(T). You can add actions to a task by calling doFirst(Action) or doLast(Action).

Groovy closures can also be used to provide a task action. When the action is executed, the closure is called withthe task as parameter. You can add action closures to a task by calling doFirst(groovy.lang.Closure) ordoLast(groovy.lang.Closure).

There are 2 special exceptions which a task action can throw to abort execution and continue without failing thebuild. A task action can abort execution of the action and continue to the next action of the task by throwing aStopActionException. A task action can abort execution of the task and continue to thenext task by throwing a StopExecutionException. Using these exceptions allows you tohave precondition actions which skip execution of the task, or part of the task, if not true.

A task may have dependencies on other tasks or might be scheduled to always run after another task.Gradle ensures that all task dependencies and ordering rules are honored when executing tasks, so that the task is executed afterall of its dependencies and any "must run after" tasks have been executed.

Dependencies to a task are controlled using dependsOn(Object...) or setDependsOn(Iterable),and mustRunAfter(Object...), setMustRunAfter(Iterable), shouldRunAfter(Object...) andsetShouldRunAfter(Iterable) are used to specify ordering between tasks. You can use objects of any ofthe following types to specify dependencies and ordering:

Execute the task only if the given closure returns true. The closure will be evaluated at task executiontime, not during configuration. The closure will be passed a single parameter, this task. If the closure returnsfalse, the task will be skipped.

The presence of incompatible tasks in the task graph will cause the configuration state to be discardedat the end of the build unless the global configuration-cache-problems option is set to warn,in which case the configuration state would still be cached in a best-effort manner as usual for the option.

Checks if the task actually did any work. Even if a Task executes, it may determine that it has nothing todo. For example, a compilation task may determine that source files have not changed since the last time a thetask was run.

Returns a directory which this task can use to write temporary files to. Each task instance is provided with aseparate temporary directory. There are no guarantees that the contents of this directory will be kept beyond theexecution of the task.

For each supplied task, this action adds a task 'ordering', and does not specify a 'dependency' between the tasks.As such, it is still possible to execute 'taskY' without first executing the 'taskX' in the example. 006ab0faaa