We have seen test flakes caused by 'concurrent map read and map write', and the race detector
reports the problem as well (prevent us from running some tests with -race).
The root of the problem is the grpc expects resolvers to be registered at init time
before any requests are made, but we were using a separate resolver for each test.
This commit introduces a resolver registry. The registry is registered as the single
resolver for the consul scheme. Each test uses the Authority section of the target
(instead of the scheme) to identify the resolver that should be used for the test.
The scheme is used for lookup, which is why it can no longer be used as the unique
key.
This allows us to use a lock around the map of resolvers, preventing the data race.
defaultMetrics was being set at package import time, which meant that it received an instance of
the original default. But lib/telemetry.InitTelemetry sets a new global when it is called.
This resulted in the metrics being sent nowhere.
This commit changes defaultMetrics to be a function, so it will return the global instance when
called. Since it is called after InitTelemetry it will return the correct metrics instance.
Rename GRPCClient to ClientConnPool. This type appears to be more of a
conn pool than a client. The clients receive the connections from this
pool.
Reduce some dependencies by adjusting the interface baoundaries.
Remove the need to create a second slice of Servers, just to pick one and throw the rest away.
Unexport serverResolver, it is not used outside the package.
Use a RWMutex for ServerResolverBuilder, some locking is read-only.
Add more godoc.
R.B. Boyer