• Zhiyi Zhang's avatar
    rtworkq: Avoid possible scenarios that an async callback could be called twice. · 7865026f
    Zhiyi Zhang authored
    Consider a thread A running waiting_item_cancelable_callback() and a thread B running queue_cancel_item(),
    which is the scenario from canceling a work item right after it gets submitted by RtwqPutWaitingWorkItem().
    When the invoke_async_callback() call in queue_cancel_item() for item key with WAIT_ITEM_KEY_MASK in
    thread B runs before the queue_release_pending_item() in waiting_item_cancelable_callback() in thread
    A, the async callback is called the first time in queue_cancel_item() with RTWQ_E_OPERATION_CANCELLED,
    then a second time in waiting_item_cancelable_callback(). We should check in queue_release_pending_item()
    whether an item is already removed by queue_cancel_item() before calling async callbacks.
    
    A different scenario could happen for scheduled_item_cancelable_callback() with the function ends
    up calling its async callback even after it has been canceled by queue_cancel_item().
    7865026f
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