mirror of https://github.com/grpc/grpc.git
The C based gRPC (C++, Python, Ruby, Objective-C, PHP, C#)
https://grpc.io/
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46 lines
2.2 KiB
46 lines
2.2 KiB
# Background # |
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In Python, multithreading is ineffective at concurrency for CPU bound tasks |
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due to the GIL (global interpreter lock). Extension modules can release |
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the GIL in CPU bound tasks, but that isn't an option in pure Python. |
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Users use libraries such as multiprocessing, subprocess, concurrent.futures.ProcessPoolExecutor, |
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etc, to work around the GIL. These modules call ```fork()``` underneath the hood. Various issues have |
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been reported when using these modules with gRPC Python. gRPC Python wraps |
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gRPC core, which uses multithreading for performance, and hence doesn't support ```fork()```. |
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Historically, we didn't support forking in gRPC, but some users seemed |
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to be doing fine until their code started to break on version 1.6. This was |
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likely caused by the addition of background c-threads and a background |
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Python thread. |
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# Current Status # |
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## 1.11 ## |
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The background Python thread was removed entirely. This allows forking |
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after creating a channel. However, the channel must not have issued any |
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RPCs prior to the fork. Attempting to fork with an active channel that |
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has been used can result in deadlocks/corrupted wire data. |
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## 1.9 ## |
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A regression was noted in cases where users are doing fork/exec. This |
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was due to ```pthread_atfork()``` handler that was added in 1.7 to partially |
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support forking in gRPC. A deadlock can happen when pthread_atfork |
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handler is running, and an application thread is calling into gRPC. |
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We have provided a workaround for this issue by allowing users to turn |
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off the handler using env flag ```GRPC_ENABLE_FORK_SUPPORT=False```. |
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This should be set whenever a user expects to always call exec |
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immediately following fork. It will disable the fork handlers. |
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## 1.7 ## |
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A ```pthread_atfork()``` handler was added in 1.7 to automatically shut down |
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the background c-threads when fork was called. This does not shut down the |
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background Python thread, so users could not have any open channels when |
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forking. |
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# Future Work # |
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## 1.13 ## |
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The workaround when using fork/exec by setting |
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```GRPC_ENABLE_FORK_SUPPORT=False``` should no longer be needed. Following |
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[this PR](https://github.com/grpc/grpc/pull/14647), fork |
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handlers will not automatically run when multiple threads are calling |
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into gRPC.
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