Re-initialize autograd engine in child processes #4158
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soumith
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apaszke
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Dec 13, 2017
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The autograd engine uses threads for backwards. These don't exist after forks and they were not being re-initialized because the Engine::start_threads_flag was already set. This re-initializes the engine in child processes, which will cause it to re-create threads when backwards() is called in the child process. Note that we only attempt to handle the common case where fork() is called while the backwards threads are idle. Fixes pytorch#3966
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| static bool _reinitialize_engine = false; | ||
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| static void _maybe_reinitialize_engine_after_fork() { | ||
| // This is "probably" thread-safe because the flag is set in a fork handler |
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The autograd engine uses threads for backwards. These don't exist after
forks and they were not being re-initialized because the
Engine::start_threads_flag was already set. This re-initializes the
engine in child processes, which will cause it to re-create threads when
backwards() is called in the child process.
Note that we only attempt to handle the common case where fork() is
called while the backwards threads are idle.
Fixes #3966