How to wait for garbage collection to complete?

Question

I was wondering is there a way to wait for GC to finish?

Lets say I'm running benchmarks:

• BenchmarkUnlimited (Does a lot of work)
• BenchmarkNumCPU (Is affected by BenchmarkUnlimited)

The problem here is that BenchmarkUnlimited creates a lot of allocations, garbage collecting all of this takes time, but BenchmarkNumCPU is already running and its results can be affected by the previous benchmark.

Is there a way to tell the go program to wait for the GC to complete before running the next benchmark?

Answer 1

The Go benchmark framework already invokes runtime.GC() before running each benchmark.

So there is no issue - you can rest assured each benchmark is started free of garbage from previous benchmarks.

See go/src/testing/benchmark.go: (also notice the comment there)

func (b *B) runN(n int) {
    benchmarkLock.Lock()
    defer benchmarkLock.Unlock()
    defer b.runCleanup(normalPanic)
    // Try to get a comparable environment for each run
    // by clearing garbage from previous runs.
    runtime.GC()                                    // <========== HERE
    b.raceErrors = -race.Errors()
    b.N = n
    b.parallelism = 1
    b.ResetTimer()
    b.StartTimer()
    b.benchFunc(b)
    b.StopTimer()
    . . .