main

Author: sharpchen

…ogramming/Task/Create & Wait & Cancel.md …llel Programming/Task/Create & Cancel.mddocs/document/Modern CSharp/docs/Parallel Programming/Task/Create & Wait & Cancel.md renamed to docs/document/Modern CSharp/docs/Parallel Programming/Task/Create & Cancel.md docs/document/Modern CSharp/docs/Parallel Programming/Task/Create & Wait & Cancel.md renamed to docs/document/Modern CSharp/docs/Parallel Programming/Task/Create & Cancel.md

@@ -1,12 +1,12 @@
-# Create & Wait & Cancel
+# Start & Cancel
 
 ## Create & Start
 
 Task can be created from the following sources:
 
 - constructors of `Task` and `Task<T>`
 - Task creation methods like `Task.Run` and `TaskFactory.StartNew`
-- `async` methods
+- `async` delegates
 
 ```cs
 var task = new Task(() => Console.WriteLine("hello"));
@@ -28,9 +28,9 @@ _ = Task.Factory.StartNew(() => Console.WriteLine("hello"));
 _ = Task.Run(() => Console.WriteLine("hello"));
 
 
-Foo(); // started automatically
+fooAsync(); // started automatically
 
-static async void Foo()
+ var fooAsync = async () =>
 {
     await Task.Run(() => Console.WriteLine("foo"));
 }
@@ -129,7 +129,7 @@ Task<int> t2 = await Task.Factory.StartNew(async () =>
 ```
 
 > [!TIP]
-> `Task.Run` does not require unwrap.
+> `Task.Run` has a implicit auto-unwrap for some of its overloads
 >```cs
 >Task<int> t = Task.Run(async () =>
 >{
@@ -149,6 +149,21 @@ Task<int> task = Task.FromResult(42);
 Console.WriteLine(task.Result); // Outputs: 42
 ```
 
+### Create as Continued Task
+
+`Task.ContinueWith` creates a task after the previous task has terminated with certain condition, and it starts simultaneously.
+Such condition can be specified by `TaskContinuationOptions` in its overloads.
+
+```cs
+Task.Run(async () =>
+{
+    await Task.Delay(100);
+}).ContinueWith(prev =>
+{
+    Console.WriteLine("Continued task started automatically!");
+}).Wait();
+```
+
 ### `Task.Run` vs `TaskFactory.StartNew`
 
 - `Task.Run`
@@ -180,58 +195,10 @@ _ = Task.Factory.StartNew(
 );
 ```
 
-## Blocking & Non-Blocking Wait
-
-Waiting a task means the execution of code is synchronous but there's a essential difference between Blocking Wait & Non-Blocking Wait
-
-- accessing for `task.Result` causing the blocking wait that blocks the main thread
-    ```cs
-    Task<int> task = new(() => 123);
-
-    task.Start();
-
-    Console.WriteLine(task.Result); // compiler knows it should wait the task blockingly // [!code highlight] 
-    // 123
-    ```
-- `await` operator waits the task without blocking the calling thread.
-    ```cs
-    int foo = await Foo(); // does not block the main thread but still synchronous
-    static async Task<int> Foo 
-    {
-        await Task.Delay(500);
-        return 123;
-    }
-    ```
-
-- `task.Wait`: to wait the task itself.
-- `Task.Wait*`: utils to wait a batch of tasks in a **blocking** manner.
-- `Task.When*`: utils to wait a batch of tasks in a **non-blocking** manner.
-
-
-A task must be started before awaiting, or the thread would be blocked forever.
-A task from `async` method is started implicitly so no worry here.
-
-To wait a task synchronously, use `await` operator before a started task object.
-
-```cs
-var task = new Task(() => Console.WriteLine("hello"));
-task.Start(); // must get it started!!! // [!code highlight] 
-await task;
-```
-
-Starting a simple task manually is quiet trivial so one should prefer `Task.Run` or `Task.Factory.StartNew`
-
-```cs
-await Task.Factory.StartNew((object? foo) =>
-{
-    Console.WriteLine(((dynamic)foo).Foo);
-}, new { Foo = 345 });
-
-await Task.Run(() => { Console.WriteLine("hello"); });
-```
-
 ## Creation Options
 
+<!--TODO: creation options-->
+
 ## Task Cancellation
 
 ### What Manage it & What Represents it
@@ -265,7 +232,7 @@ Task task = new(() =>
     {
         if (token.IsCancellationRequested)
         {
-            throw new OperationCanceledException(); // does not terminate the whole program // [!code highlight] 
+            throw new OperationCanceledException(token); // does not terminate the whole program // [!code highlight] 
         }
         Console.WriteLine("working with task");
     }
@@ -301,7 +268,27 @@ So this checking on whether cancellation suceeded requires a validation on the t
 <!--TODO: add example-->
 
 ```cs
+using CancellationTokenSource cts = new(5000);
+CancellationToken token = cts.Token;
+
+Task task = Task.Factory.StartNew(() =>
+{
+    while (true)
+    {
+        Console.WriteLine("operation...");
+        token.ThrowIfCancellationRequested();
+        Thread.Sleep(1000);
+    }
+}, cts.Token); // it's oke, all tokens from same source are identical
 
+try
+{
+    task.Wait();
+}
+catch (AggregateException)
+{
+    Console.WriteLine(task.Status); // Canceled
+}
 ```
 
 > [!NOTE]
@@ -364,6 +351,8 @@ Console.WriteLine("task finished");
 
 After cancellation simply means chaining a event after previous task, and allowing access to previous task in the callback so you can do things conditionally.
 
+<!--TODO: faulted example is not right, the task is not canceled correctly-->
+
 ```cs
 var cts = new CancellationTokenSource();
 var token = cts.Token;
@@ -395,6 +384,22 @@ Console.WriteLine("task finished");
 
 You may wanted to combine tokens from different sources to perform a simultaneous cancellation even they're from different sources.
 
+### Common Practice
+
+```cs
+using (CancellationTokenSource cts = new(timeout))
+{
+    try
+    {
+        await task(foo, cts.Token);
+    }
+    catch (OperationCanceledException)
+    {
+        Console.WriteLine("canceled");
+    }
+}
+```
+
 ## Sleeping on Thread
 
 - `Thread.Sleep`: pauses the thread and allows the scheduler to run another thread while sleeping, for the efficiency.

docs/document/Modern CSharp/docs/Parallel Programming/Task/Exception Handling.md

@@ -17,14 +17,22 @@ Task task2 = Task.Run(() =>
 // program was not terminated
 ```
 
+## What Might be Thrown
+
+<!--TODO:might throw TaskCanceledException in some cases, does OperationCancelledException thrown?-->
+Exception can be thrown and catched from a task for the following scenarios:
+
+- `AggregateException` can be thrown from:
+    - `task.Wait();`
+    - `Task.Wait*`
+    - `task.Result`
+- Direct exception can be thrown from:
+    - `await Task.When*`
+    - `await task`
+    - `task.GetAwaiter().GetResult()`
 
 ## Catch in Statement
 
-Exception can be thrown and catched from a task for the following scenarios:
-- `await task;`
-- `task.Wait();`
-- `task.Result`
-- `task.GetAwaiter().GetResult()`
 
 Exception yield from tasks is **always** a composite exception `AggregateException` **unless the exception is `OperationCancelledException` and the task has cancelled.**
 
@@ -88,13 +96,14 @@ catch (AggregateException ex)
 }
 ```
 
-## Access Exception From Task
+
+## Handle in Continued Tasks
 
 Task object itself can hold an `AggregateException` as a property.
 So you may handle them in a continued task or a post operation.
 
 ```cs
-_ = Task.Run(() => throw new AccessViolationException()).ContinueWith(prev =>
+_ = Task.Factory.StartNew(() => throw new AccessViolationException()).ContinueWith(prev =>
 {
     prev.Exception?.Handle(iex =>
     {

docs/document/Modern CSharp/docs/Parallel Programming/Task/Task Status.md

@@ -1,5 +1,7 @@
 # Task Status
 
+**One should always access tasks status in either `try..catch` statement or continued tasks**
+
 ## Created
 
 Status `Created` is assigned when on task creation but usually seen on tasks created from constructors since other creation methods always start implicitly
@@ -9,23 +11,29 @@ Task task = new Task(() => { });
 Console.WriteLine(task.Status); // Created
 ```
 
+## WaitingForActivation
+
 ## WaitingForRun
 
-A task has been scheduled by scheduler but has not yet behun execution
+A task has been scheduled by scheduler but has not yet begun execution
 
-## RunToCompletion
+## RanToCompletion
 
-Implying a task has completed successfully.
-A task ran to end or terminated by returing a value has status `RunToCompletion`
+A task ran to end or terminated by `return` or ran to end has status `RanToCompletion`
 
 ## Canceled
 
-A successful cancellation happens **when all of the following were satisfied**
-- `OperationCanceledException`(or its derived exception type) is thrown
+A successful cancellation happens **when all of the three conditions were satisfied**
+- `OperationCanceledException`(or its derived exception type such as `TaskCanceledException`) is thrown
 - `token.IsCancellationRequested` is true
-- `token` in closure passed to `OperationCanceledException` equals `token` as parameter
+- `token` in closure passed to `OperationCanceledException` equals `token` as parameter on task creation
+
+There's a special case that can result in Canceled status when a task requires unwrap.
+If the inner task creation was Faulted because of a thrown of `OperationCanceledException`, the unwrap process would set the status of outer task to Canceled.
+Otherwise it would just remain Faulted.
 
 ```cs
+// compiler would choose a Task.Run(Func<Task> function) here
 var task = Task.Run(() =>
 {
     throw new OperationCanceledException(); // [!code highlight] 
@@ -39,18 +47,37 @@ catch (AggregateException)
 {
     Console.WriteLine(task.Status); // Cancelled // [!code highlight] 
 }
+// Explicit unwrap have the same behavior
+// async was marked here because TaskFactory.StartNew does not have such overload resolution like Task.Run
+Task task2 = Task.Factory.StartNew(async () =>
+{
+    await Task.Delay(100);
+    throw new Exception(); // it's another type of Exception this time // [!code highlight] 
+}).Unwrap();
+
+try
+{
+    task2.Wait();
+}
+catch (AggregateException)
+{
+    Console.WriteLine(task2.Status); // Faulted // [!code highlight] 
+}
 ```
 
 ## Faulted
 
-Faulted happens on:
+Faulted happens on one of the scenarios:
 
 - Any exception besides `OperationCanceledException` was thrown.
 - `OperationCanceledException` is thrown && (`token.IsCancellationRequested` is false || `token` in closure passed to `OperationCanceledException` != `token` as parameter)
+- Any exception is not `OperationCanceledException` was thrown on task creation. A wait on the task created anyway results Faulted.
+
 
 ```cs
-var task = Task.Run(() =>
+Task task = Task.Factory.StartNew(async () =>
 {
+    await Task.Delay(100);
     throw new Exception(); // not an OperationCanceledException // [!code highlight] 
 });