【Flink】Flink 1.12.2 TaskSlot

1.概述

转载：Flink 1.12.2 源码浅析 : TaskSlot

属于同一slot的多个{@link TaskSlotPayload tasks}的容器。

TaskSlot 可以处于以下状态之一：

1. 空闲[Free]-slot为空，未分配给作业
2. 释放中[Releasing]-slot变空后即将释放。
3. 已分配[Allocated]-已为作业分配slot。
4. 活动[Active]-slot正由job manager使用， job manager 是分配job 的负责人

• 只有在task slot处于空闲状态时才能分配它。

• 分配的task slot可以转换为活动状态。

• 活动slot允许从相应作业添加具有正确分配id的任务。

• 活动slot可以标记为非活动，从而将状态设置回已分配状态。

• 分配的或活动的slot只有在为空时才能释放。

• 如果它不是空的，那么它的状态可以设置为releasing，表示一旦它变空就可以被释放。

二 . 属性

    /**
     *  task slot的下标索引
     * Index of the task slot.
     * */
    private final int index;

    /**
     * 此插槽的资源特征。
     * Resource characteristics for this slot.
     * */
    private final ResourceProfile resourceProfile;

    /**
     * 在这个slot中运行的task
     * Tasks running in this slot.
     * */
    private final Map<ExecutionAttemptID, T> tasks;

    /**
     * 内存管理
     */
    private final MemoryManager memoryManager;

    /**
     * slot的状态:
     * 1. ACTIVE, // Slot is in active use by a job manager responsible for a job
     * 2. ALLOCATED, // Slot has been allocated for a job but not yet given to a job manager
     * 3. RELEASING // Slot is not empty but tasks are failed. Upon removal of all tasks, it will be released
     *
     * State of this slot. */
    private TaskSlotState state;

    /**
     * 已分配插槽的 job id。
     * Job id to which the slot has been allocated.
     * */
    private final JobID jobId;

    /**
     * 此插槽的Allocation id。
     * Allocation id of this slot.
     * */
    private final AllocationID allocationId;

    /**
     * 当插槽被释放和关闭时，关闭操作完成。
     * The closing future is completed when the slot is freed and closed.
     * */
    private final CompletableFuture<Void> closingFuture;

    /** 
     * {@link Executor}用于后台操作，例如验证所有已释放的托管内存
     * {@link Executor} for background actions, e.g. verify all managed memory released. 
     * */
    private final Executor asyncExecutor;

Slot的状态

ACTIVE : Slot 已经被 job manager 使用
ALLOCATED : Slot 已经被分配,但是尚未分配Job manager使用.
RELEASING : Slot 不为空,但task失败. 在移除所有任务后，它将被释放 .

三. 方法

3.1. 任务相关

3.1.1. 获取标识

    /**
     * Generate the slot offer from this TaskSlot.
     *
     * @return The sot offer which this task slot can provide
     */
    public SlotOffer generateSlotOffer() {
        Preconditions.checkState(
                TaskSlotState.ACTIVE == state || TaskSlotState.ALLOCATED == state,
                "The task slot is not in state active or allocated.");
        Preconditions.checkState(allocationId != null, "The task slot are not allocated");

        return new SlotOffer(allocationId, index, resourceProfile);
    }

3.1.2. 添加任务

将给定任务添加到任务slot。
仅当还没有另一个具有相同执行尝试ID的任务添加到任务slot时，才有可能。
在这种情况下，该方法返回true。
否则，任务slot将保持不变，并返回false。
如果任务slot状态未激活，则会抛出{@link IllegalStateException}。
如果任务的作业ID和分配ID与为其分配了任务slot的作业ID和分配ID不匹配，则会抛出{@link IllegalArgumentException}。

    /**
     * 将给定任务添加到任务slot。
     * 仅当还没有另一个具有相同执行尝试ID的任务添加到任务slot时，才有可能。
     * 在这种情况下，该方法返回true。
     * 否则，任务slot将保持不变，并返回false。
     *
     * 如果任务slot状态未激活，则会抛出{@link IllegalStateException}。
     *
     * 如果任务的作业ID和分配ID与为其分配了任务slot的作业ID和分配ID不匹配，则会抛出{@link IllegalArgumentException}。
     *
     * Add the given task to the task slot. This is only possible if there is not already another
     * task with the same execution attempt id added to the task slot. In this case, the method
     * returns true. Otherwise the task slot is left unchanged and false is returned.
     *
     * 
In case that the task slot state is not active an {@link IllegalStateException} is thrown.
     * In case that the task's job id and allocation id don't match with the job id and allocation
     * id for which the task slot has been allocated, an {@link IllegalArgumentException} is thrown.
     *
     * @param task to be added to the task slot
     * @throws IllegalStateException if the task slot is not in state active
     * @return true if the task was added to the task slot; otherwise false
     */
    public boolean add(T task) {
        // Check that this slot has been assigned to the job sending this task
        Preconditions.checkArgument(
                task.getJobID().equals(jobId),
                "The task's job id does not match the "
                        + "job id for which the slot has been allocated.");
        Preconditions.checkArgument(
                task.getAllocationId().equals(allocationId),
                "The task's allocation "
                        + "id does not match the allocation id for which the slot has been allocated.");
        Preconditions.checkState(
                TaskSlotState.ACTIVE == state, "The task slot is not in state active.");

        T oldTask = tasks.put(task.getExecutionId(), task);

        if (oldTask != null) {
            tasks.put(task.getExecutionId(), oldTask);
            return false;
        } else {
            return true;
        }
    }

3.1.3. 获取任务

    /**
     * Get all tasks running in this task slot.
     *
     * @return Iterator to all currently contained tasks in this task slot.
     */
    public Iterator<T> getTasks() {
        return tasks.values().iterator();
    }

3.1.4. 移除任务

删除由给定的execution attempt id标识的任务。

    /**
     * Remove the task identified by the given execution attempt id.
     *
     * @param executionAttemptId identifying the task to be removed
     * @return The removed task if there was any; otherwise null.
     */
    public T remove(ExecutionAttemptID executionAttemptId) {
        return tasks.remove(executionAttemptId);
    }

3.1.5. 清理所有task

    /** Removes all tasks from this task slot. */
    public void clear() {
        tasks.clear();
    }

3.2. 状态相关

名称	描述
isActive	状态是否为ACTIVE
isAllocated	状态为ACTIVE或者ALLOCATED
isReleasing	状态是否为RELEASING
markActive	标记状态为ACTIVE
markInactive	标记状态为ALLOCATED
closeAsync	关闭,标记状态为RELEASING

3.3. get/set相关

index: int
resourceProfile: ResourceProfile
memoryManager: MemoryManager
state: TaskSlotState
jobId: JobID
allocationId: AllocationID
empty: boolean
releasing: boolean
tasks: Iterator<T>