114 lines
6.3 KiB
XML
114 lines
6.3 KiB
XML
<?xml version="1.0" encoding="UTF-8" ?>
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<class name="WorkerThreadPool" inherits="Object" version="4.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="../class.xsd">
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<brief_description>
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A singleton that allocates some [Thread]s on startup, used to offload tasks to these threads.
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</brief_description>
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<description>
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The [WorkerThreadPool] singleton allocates a set of [Thread]s (called worker threads) on project startup and provides methods for offloading tasks to them. This can be used for simple multithreading without having to create [Thread]s.
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Tasks hold the [Callable] to be run by the threads. [WorkerThreadPool] can be used to create regular tasks, which will be taken by one worker thread, or group tasks, which can be distributed between multiple worker threads. Group tasks execute the [Callable] multiple times, which makes them useful for iterating over a lot of elements, such as the enemies in an arena.
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Here's a sample on how to offload an expensive function to worker threads:
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[codeblocks]
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[gdscript]
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var enemies = [] # An array to be filled with enemies.
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func process_enemy_ai(enemy_index):
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var processed_enemy = enemies[enemy_index]
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# Expensive logic...
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func _process(delta):
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var task_id = WorkerThreadPool.add_group_task(process_enemy_ai, enemies.size())
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# Other code...
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WorkerThreadPool.wait_for_group_task_completion(task_id)
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# Other code that depends on the enemy AI already being processed.
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[/gdscript]
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[csharp]
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private List<Node> _enemies = new List<Node>(); // A list to be filled with enemies.
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private void ProcessEnemyAI(int enemyIndex)
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{
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Node processedEnemy = _enemies[enemyIndex];
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// Expensive logic here.
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}
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public override void _Process(double delta)
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{
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long taskId = WorkerThreadPool.AddGroupTask(Callable.From<int>(ProcessEnemyAI), _enemies.Count);
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// Other code...
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WorkerThreadPool.WaitForGroupTaskCompletion(taskId);
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// Other code that depends on the enemy AI already being processed.
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}
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[/csharp]
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[/codeblocks]
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The above code relies on the number of elements in the [code]enemies[/code] array remaining constant during the multithreaded part.
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[b]Note:[/b] Using this singleton could affect performance negatively if the task being distributed between threads is not computationally expensive.
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</description>
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<tutorials>
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<link title="Using multiple threads">$DOCS_URL/tutorials/performance/using_multiple_threads.html</link>
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<link title="Thread-safe APIs">$DOCS_URL/tutorials/performance/thread_safe_apis.html</link>
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</tutorials>
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<methods>
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<method name="add_group_task">
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<return type="int" />
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<param index="0" name="action" type="Callable" />
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<param index="1" name="elements" type="int" />
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<param index="2" name="tasks_needed" type="int" default="-1" />
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<param index="3" name="high_priority" type="bool" default="false" />
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<param index="4" name="description" type="String" default="""" />
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<description>
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Adds [param action] as a group task to be executed by the worker threads. The [Callable] will be called a number of times based on [param elements], with the first thread calling it with the value [code]0[/code] as a parameter, and each consecutive execution incrementing this value by 1 until it reaches [code]element - 1[/code].
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The number of threads the task is distributed to is defined by [param tasks_needed], where the default value [code]-1[/code] means it is distributed to all worker threads. [param high_priority] determines if the task has a high priority or a low priority (default). You can optionally provide a [param description] to help with debugging.
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Returns a group task ID that can be used by other methods.
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</description>
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</method>
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<method name="add_task">
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<return type="int" />
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<param index="0" name="action" type="Callable" />
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<param index="1" name="high_priority" type="bool" default="false" />
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<param index="2" name="description" type="String" default="""" />
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<description>
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Adds [param action] as a task to be executed by a worker thread. [param high_priority] determines if the task has a high priority or a low priority (default). You can optionally provide a [param description] to help with debugging.
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Returns a task ID that can be used by other methods.
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</description>
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</method>
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<method name="get_group_processed_element_count" qualifiers="const">
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<return type="int" />
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<param index="0" name="group_id" type="int" />
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<description>
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Returns how many times the [Callable] of the group task with the given ID has already been executed by the worker threads.
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[b]Note:[/b] If a thread has started executing the [Callable] but is yet to finish, it won't be counted.
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</description>
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</method>
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<method name="is_group_task_completed" qualifiers="const">
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<return type="bool" />
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<param index="0" name="group_id" type="int" />
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<description>
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Returns [code]true[/code] if the group task with the given ID is completed.
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</description>
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</method>
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<method name="is_task_completed" qualifiers="const">
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<return type="bool" />
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<param index="0" name="task_id" type="int" />
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<description>
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Returns [code]true[/code] if the task with the given ID is completed.
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</description>
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</method>
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<method name="wait_for_group_task_completion">
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<return type="void" />
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<param index="0" name="group_id" type="int" />
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<description>
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Pauses the thread that calls this method until the group task with the given ID is completed.
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</description>
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</method>
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<method name="wait_for_task_completion">
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<return type="int" enum="Error" />
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<param index="0" name="task_id" type="int" />
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<description>
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Pauses the thread that calls this method until the task with the given ID is completed.
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Returns [constant @GlobalScope.OK] if the task could be successfully awaited.
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Returns [constant @GlobalScope.ERR_INVALID_PARAMETER] if a task with the passed ID does not exist (maybe because it was already awaited and disposed of).
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Returns [constant @GlobalScope.ERR_BUSY] if the call is made from another running task and, due to task scheduling, the task to await is at a lower level in the call stack and therefore can't progress. This is an advanced situation that should only matter when some tasks depend on others.
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</description>
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</method>
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</methods>
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</class>
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