This pkg implements a context which can be used globally in a server. Incoming request contexts can then be merged with this global context. On cancellation of the global or a request context the merged context gets also canceled. This is especially useful for canceling long running request before starting a graceful server shutdown.
A more concrete example here is when using grpc streams then such a context can be useful on the grpc server to cancel stream request before shutting down the server.
rootCtx, rootCancel := mergectx.ContextWithCancel(context.Background())
loop := 10
var wg sync.WaitGroup
wg.Add(loop)
for i := 0; i < loop; i++ {
// merge a context with the root context
ctx, cancel := rootCtx.Merge(context.Background())
go func() {
<-ctx.Done()
wg.Done()
cancel()
}()
}
// cancelling the root context now also cancels all the merged contexts
rootCancel()
wg.Wait()
fmt.Printf("stopped\n")There is also a simpler approach to the problem
func mergeCtx(left, right context.Context) (context.Context, context.CancelFunc) {
ctx, cancel := context.WithCancel(right)
go func() {
select {
case <-left.Done():
cancel()
case <-ctx.Done():
}
}()
return ctx, cancel
}With this implementation cancelling the left context also cancels the merged context.
Since this approach involves creating a goroutine with every merge its a bit slower. The benachmark BenchmarkMergeWithExtraGoroutine uses this approach.
BenchmarkRootContext
BenchmarkRootContext-16 975492 1229 ns/op 10.58 MB/s
BenchmarkRaw
BenchmarkRaw-16 2664434 444 ns/op 29.26 MB/s
BenchmarkContextWithCancel
BenchmarkContextWithCancel-16 1467096 794 ns/op 16.38 MB/s
BenchmarkContextWithParentCancel
BenchmarkContextWithParentCancel-16 983482 1205 ns/op 10.79 MB/s
BenchmarkContextWithTimeout
BenchmarkContextWithTimeout-16 130044 9180 ns/op 1.42 MB/s
BenchmarkMergeWithExtraGoroutine
BenchmarkMergeWithExtraGoroutine-16 475257 2325 ns/op 5.59 MB/s