wehub-resource-sync
47 lines
1.6 KiB
ReStructuredText
47 lines
1.6 KiB
ReStructuredText
Nested Remote Functions
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=======================
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Remote functions can call other remote functions, resulting in nested tasks.
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For example, consider the following.
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.. literalinclude:: ../doc_code/nested-tasks.py
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:language: python
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:start-after: __nested_start__
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:end-before: __nested_end__
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Then calling ``g`` and ``h`` produces the following behavior.
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.. code-block:: bash
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>>> ray.get(g.remote())
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[ObjectRef(b1457ba0911ae84989aae86f89409e953dd9a80e),
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ObjectRef(7c14a1d13a56d8dc01e800761a66f09201104275),
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ObjectRef(99763728ffc1a2c0766a2000ebabded52514e9a6),
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ObjectRef(9c2f372e1933b04b2936bb6f58161285829b9914)]
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>>> ray.get(h.remote())
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[1, 1, 1, 1]
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**One limitation** is that the definition of ``f`` must come before the
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definitions of ``g`` and ``h`` because as soon as ``g`` is defined, it
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will be pickled and shipped to the workers, and so if ``f`` hasn't been
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defined yet, the definition will be incomplete.
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Yielding Resources While Blocked
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--------------------------------
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Ray will release CPU resources when being blocked. This prevents
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deadlock cases where the nested tasks are waiting for the CPU
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resources held by the parent task.
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Consider the following remote function.
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.. literalinclude:: ../doc_code/nested-tasks.py
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:language: python
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:start-after: __yield_start__
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:end-before: __yield_end__
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When a ``g`` task is executing, it will release its CPU resources when it gets
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blocked in the call to ``ray.get``. It will reacquire the CPU resources when
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``ray.get`` returns. It will retain its GPU resources throughout the lifetime of
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the task because the task will most likely continue to use GPU memory.
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