70 lines
2.1 KiB
Go
70 lines
2.1 KiB
Go
package balancer
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import (
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"fmt"
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"sync"
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gbalancer "google.golang.org/grpc/balancer"
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)
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// BuilderName should be given in gRPC service configuration to enable our
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// custom balancer. It refers to this package's global registry, rather than
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// an instance of Builder to enable us to add and remove builders at runtime,
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// specifically during tests.
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const BuilderName = "consul-internal"
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// gRPC's balancer.Register method is thread-unsafe because it mutates a global
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// map without holding a lock. As such, it's expected that you register custom
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// balancers once at the start of your program (e.g. a package init function).
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//
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// In production, this is fine. Agents register a single instance of our builder
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// and use it for the duration. Tests are where this becomes problematic, as we
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// spin up several agents in-memory and register/deregister a builder for each,
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// with its own agent-specific state, logger, etc.
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//
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// To avoid data races, we call gRPC's Register method once, on-package init,
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// with a global registry struct that implements the Builder interface but
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// delegates the building to N instances of our Builder that are registered and
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// deregistered at runtime. We the dial target's host (aka "authority") which
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// is unique per-agent to pick the correct builder.
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func init() {
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gbalancer.Register(globalRegistry)
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}
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var globalRegistry = ®istry{
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byAuthority: make(map[string]*Builder),
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}
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type registry struct {
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mu sync.RWMutex
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byAuthority map[string]*Builder
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}
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func (r *registry) Build(cc gbalancer.ClientConn, opts gbalancer.BuildOptions) gbalancer.Balancer {
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r.mu.RLock()
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defer r.mu.RUnlock()
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auth := opts.Target.URL.Host
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builder, ok := r.byAuthority[auth]
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if !ok {
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panic(fmt.Sprintf("no gRPC balancer builder registered for authority: %q", auth))
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}
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return builder.Build(cc, opts)
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}
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func (r *registry) Name() string { return BuilderName }
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func (r *registry) register(auth string, builder *Builder) {
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r.mu.Lock()
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defer r.mu.Unlock()
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r.byAuthority[auth] = builder
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}
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func (r *registry) deregister(auth string) {
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r.mu.Lock()
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defer r.mu.Unlock()
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delete(r.byAuthority, auth)
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}
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