Backport of grpc: fix data race in balancer registration into release/1.15.x #17351
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Registering gRPC balancers is thread-unsafe because they are stored in a global map variable that is accessed without holding a lock. Therefore, it's expected that balancers are registered _once_ at the beginning of your program (e.g. in a package `init` function) and certainly not after you've started dialing connections, etc. > NOTE: this function must only be called during initialization time > (i.e. in an init() function), and is not thread-safe. While this is fine for us in production, it's challenging for tests that spin up multiple agents in-memory. We currently register a balancer per- agent which holds agent-specific state that cannot safely be shared. This commit introduces our own registry that _is_ thread-safe, and implements the Builder interface such that we can call gRPC's `Register` method once, on start-up. It uses the same pattern as our resolver registry where we use the dial target's host (aka "authority"), which is unique per-agent, to determine which builder to use.
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Backport
This PR is auto-generated from #16229 to be assessed for backporting due to the inclusion of the label backport/1.15.
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The person who merged in the original PR is:
@boxofrad
This person should manually cherry-pick the original PR into a new backport PR,
and close this one when the manual backport PR is merged in.
The below text is copied from the body of the original PR.
Description
Registering gRPC balancers is thread-unsafe because they are stored in a global map variable that is accessed without holding a lock. Therefore, it's expected that balancers are registered once at the beginning of your program (e.g. in a package
initfunction) and certainly not after you've started dialing connections, etc.While this is fine for us in production, it's challenging for tests that spin up multiple agents in-memory. We currently register a balancer per-agent which holds agent-specific state that cannot safely be shared.
This commit introduces our own registry that is thread-safe, and implements the
Builderinterface such that we can call gRPC'sRegistermethod once, on start-up. It uses the same pattern as our resolver registry where we use the dial target's host (aka "authority"), which is unique per-agent, to determine which builder to use.Overview of commits