Fix race in writing state during hard cancelation #17323
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If the user wishes to interrupt the running operation, only the first interrupt was communicated to the operation by canceling the provided context. A second interrupt would start the shutdown process, but not communicate this to the running operation. This order of event could cause partial writes of state. What would happen is that once the command returns, the plugin system would stop the provider processes. Once the provider processes dies, all pending Eval operations would return return with an error, and quickly cause the operation to complete. Since the backend code didn't know that the process was shutting down imminently, it would continue by attempting to write out the last known state. Under the right conditions, the process would exit part way through the writing of the state file. Add Stop and Cancel CancelFuncs to the RunningOperation, to allow it to easily differentiate between the two signals. The backend will then be able to detect a shutdown and abort more gracefully. In order to ensure that the backend is not in the process of writing the state out, the command will always attempt to wait for the process to complete after cancellation.
Create a single command method for running and operation with cancellation.
The error was being silently dropped before. There is an interpolation error, because the plan is canceled before some of the resources can be evaluated. There might be a better way to handle this in the walk cancellation, but the behavior has not changed. Make the plan and apply shutdown match implementation-wise
Moves the nested select statements for backend operations into a single function. The only difference in this part was that apply called PersistState, which should be harmless regardless of the type of operation being run.
apparentlymart
approved these changes
Feb 13, 2018
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If the user wishes to interrupt the running operation, only the first
interrupt was communicated to the operation by canceling the provided
context. A second interrupt would start the shutdown process, but not
communicate this to the running operation. This order of events could
cause partial writes of state.
What would happen is that once the command returns, the plugin system
would stop the provider processes. Once the provider processes dies, all
pending Eval operations would return return with an error, and quickly
cause the operation to complete. Since the backend code didn't know that
the process was shutting down imminently, it would continue by
attempting to write out the last known state. Under the right
conditions, the process would exit part way through the writing of the
state file.
Add Stop and Cancel CancelFuncs to the RunningOperation, to allow it to
easily differentiate between the two signals. The backend will then be
able to detect a shutdown and abort more gracefully.
In order to ensure that the backend is not in the process of writing the
state out, the command will always attempt to wait for the process to
complete after cancellation.
fixes #17282