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# furnished to do so, subject to the following conditions:
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# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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from contextlib import contextmanager

import torch


class StreamFork:
    def __init__(self, aux_stream: torch.cuda.Stream | None):
        self.aux_stream = aux_stream
        self.fork_event = torch.cuda.Event() if aux_stream is not None else None
        self.join_event = torch.cuda.Event() if aux_stream is not None else None
        self._active = False
        self._current: torch.cuda.Stream | None = None

    @contextmanager
    def scope(self, *, enable: bool):
        self._active = enable and self.aux_stream is not None
        if self._active:
            self._current = torch.cuda.current_stream()
            self.fork_event.record(self._current)
        try:
            yield self
        finally:
            if self._active:
                self.join_event.wait(self._current)
                self._active = False
                self._current = None

    @contextmanager
    def branch(self):
        if not self._active:
            yield
            return
        with torch.cuda.stream(self.aux_stream):
            self.fork_event.wait(self.aux_stream)
            yield
            self.join_event.record(self.aux_stream)