[Disco] Treat hangup of disco worker process as kShutdown #16989
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Prior to this commit, each disco worker needed to receive `DiscoAction::kShutdown` in order to close cleanly. While this is sent from the destructor of `ProcessSessionObj`, which owns the worker processes, this does not guarantee that the disco workers will receive the shutdown command. For example, the controller process holding the `ProcessSessionObj` may reach a timeout and be terminated, preventing it from sending the `DiscoAction::kShutdown` command. This commit updates the disco worker to check for a closed pipe that occurs between two packets, and to treat this as if the `DiscoAction::kShutdown` command were received. A closed pipe that occurs at any other location is still treated as an error and reported.
masahi
approved these changes
May 13, 2024
Lunderberg
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May 14, 2024
This resolves a conflict between two recent changes. In apache#16989, reads of size zero are used to identify hangups in `ProcessSession`. In apache#16992, reads of size zero are treated as an error to avoid infinite loops while waiting for data to be ready. For a long-term resolution, the `dmlc::Stream` interface will need to be updated, so that the `Write` method returns the number of bytes written, just as the `Read` method currently does. This will allow the calling scope to verify the number of bytes received.
Lunderberg
added a commit
that referenced
this pull request
May 15, 2024
This resolves a conflict between two recent changes. In #16989, reads of size zero are used to identify hangups in `ProcessSession`. In #16992, reads of size zero are treated as an error to avoid infinite loops while waiting for data to be ready. For a long-term resolution, the `dmlc::Stream` interface will need to be updated, so that the `Write` method returns the number of bytes written, just as the `Read` method currently does. This will allow the calling scope to verify the number of bytes received.
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Prior to this commit, each disco worker needed to receive
DiscoAction::kShutdownin order to close cleanly. While this is sent from the destructor ofProcessSessionObj, which owns the worker processes, this does not guarantee that the disco workers will receive the shutdown command. For example, the controller process holding theProcessSessionObjmay reach a timeout and be terminated, preventing it from sending theDiscoAction::kShutdowncommand.This commit updates the disco worker to check for a closed pipe that occurs between two packets, and to treat this as if the
DiscoAction::kShutdowncommand were received. A closed pipe that occurs at any other location is still treated as an error and reported.