A context models a program's call tree, and is used as a mechanism to propagate cancellation requests to every thread created within a scope.

Every thread is provided its own context, which is derived from its scope.

A thread can query whether its context has been cancelled, which is a suggestion to perform a graceful termination.

Perform an IO action in the global context. The global context cannot be cancelled.

A scope delimits the lifetime of all threads created within it.

Open a scope, perform an IO action with it, then close the scope.

When the scope is closed, all remaining threads created within it are killed.

Throws:

• The exception thrown by the callback to scoped itself, if any.
• ThreadFailed containing the first exception a thread created with fork throws, if any.

Examples

scoped \scope -> do
  fork_ scope worker1
  fork_ scope worker2
  wait scope

Wait until all threads created within a scope finish.

STM variant of wait.

Variant of wait that waits for up to the given duration. This is useful for giving threads some time to fulfill a cancellation request before killing them.

A running thread.

Create a thread within a scope to compute a value concurrently.

If the thread throws an exception, the exception is wrapped in ThreadFailed and immediately propagated up the call tree to the thread that opened its scope, unless that exception is a CancelToken that fulfills a cancellation request.

Throws:

• Calls error if the scope is closed.

Variant of fork that does not return a handle to the created thread.

Throws:

• Calls error if the scope is closed.

Variant of fork that provides the thread a function that unmasks asynchronous exceptions.

Throws:

• Calls error if the scope is closed.

Variant of forkWithUnmask that does not return a handle to the created thread.

Throws:

• Calls error if the scope is closed.

Create a thread within a scope to compute a value concurrently.

Throws:

• Calls error if the scope is closed.

Variant of async that provides the thread a function that unmasks asynchronous exceptions.

Throws:

• Calls error if the scope is closed.

Wait for a thread to finish.

Throws:

• ThreadFailed if the thread threw an exception and was created with fork.

STM variant of await.

Throws:

• ThreadFailed if the thread threw an exception and was created with fork.

Variant of await that waits for up to the given duration.

Throws:

• ThreadFailed if the thread threw an exception and was created with fork.

Cancel all contexts derived from a scope.

Return whether the current context is cancelled.

Threads running in a cancelled context should terminate as soon as possible. The cancel token may be thrown to fulfill the cancellation request in case the thread is unable or unwilling to terminate normally with a value.

STM variant of cancelled; blocks until the current context is cancelled.

A cancel token represents a request for cancellation; this request can be fulfilled by throwing the token as an exception.

A length of time with microsecond precision. Numeric literals are treated as seconds.

One microsecond.

One millisecond.

One second.

Wait for an STM action to return an IO action, or if the given duration elapses, return the given IO action instead.

Context-aware, duration-based threadDelay.

Throws:

• Throws CancelToken if the current context is cancelled.

A thread failed, either by throwing or being thrown an exception.