Thread

Inherits: RefCounted < Object

A unit of execution in a process.

Description

A unit of execution in a process. Can run methods on Objects simultaneously. The use of synchronization via Mutex or Semaphore is advised if working with shared objects.

Warning:

To ensure proper cleanup without crashes or deadlocks, when a Thread‘s reference count reaches zero and it is therefore destroyed, the following conditions must be met:

• It must not have any Mutex objects locked.

• It must not be waiting on any Semaphore objects.

• wait_to_finish should have been called on it.

Tutorials

• Using multiple threads

• Thread-safe APIs

• 3D Voxel Demo

Methods

Enumerations

enum Priority:

Priority PRIORITY_LOW = 0

A thread running with lower priority than normally.

Priority PRIORITY_NORMAL = 1

A thread with a standard priority.

Priority PRIORITY_HIGH = 2

A thread running with higher priority than normally.

Method Descriptions

String get_id ( ) const

Returns the current Thread‘s ID, uniquely identifying it among all threads. If the Thread has not started running or if wait_to_finish has been called, this returns an empty string.

bool is_alive ( ) const

Returns true if this Thread is currently running the provided function. This is useful for determining if wait_to_finish can be called without blocking the calling thread.

To check if a Thread is joinable, use is_started.

bool is_started ( ) const

Returns true if this Thread has been started. Once started, this will return true until it is joined using wait_to_finish. For checking if a Thread is still executing its task, use is_alive.

void set_thread_safety_checks_enabled ( bool enabled ) static

Sets whether the thread safety checks the engine normally performs in methods of certain classes (e.g., Node) should happen on the current thread.

The default, for every thread, is that they are enabled (as if called with enabled being true).

Those checks are conservative. That means that they will only succeed in considering a call thread-safe (and therefore allow it to happen) if the engine can guarantee such safety.

Because of that, there may be cases where the user may want to disable them (enabled being false) to make certain operations allowed again. By doing so, it becomes the user’s responsibility to ensure thread safety (e.g., by using Mutex) for those objects that are otherwise protected by the engine.

Note: This is an advanced usage of the engine. You are advised to use it only if you know what you are doing and there is no safer way.

Note: This is useful for scripts running on either arbitrary Thread objects or tasks submitted to the WorkerThreadPool. It doesn’t apply to code running during Node group processing, where the checks will be always performed.

Note: Even in the case of having disabled the checks in a WorkerThreadPool task, there’s no need to re-enable them at the end. The engine will do so.

Error start ( Callable callable, Priority priority=1 )

Starts a new Thread that calls callable.

If the method takes some arguments, you can pass them using Callable.bind.

The priority of the Thread can be changed by passing a value from the Priority enum.

Returns @GlobalScope.OK on success, or @GlobalScope.ERR_CANT_CREATE on failure.

Variant wait_to_finish ( )

Joins the Thread and waits for it to finish. Returns the output of the Callable passed to start.

Should either be used when you want to retrieve the value returned from the method called by the Thread or before freeing the instance that contains the Thread.

To determine if this can be called without blocking the calling thread, check if is_alive is false.

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© Copyright 2014-present Juan Linietsky, Ariel Manzur and the Godot community (CC BY 3.0). Revision 53e837c6.

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