compare sync/atomic vs add operation

Why golang have AddInt32, not only use i += num model?

Goroutine/Coroutine is one of best features in golang, we always over use goroutine.

If multiple goroutine write the shared memory, the error will happened.

Run the programming, we have counter for counting adding.

go run add_op.go
# counter: {count:1815}

go run add_op.go
# counter: {count:1282}

We add 2000 times, but result is wrong.

Why?

Because we use two goroutine to write the same memory (count in counter).

How to solve this?

1. Use mutex.

go run add_op_with_mutex.go
# counter: {count:2000 mu:{state:0 sema:0}}

2. Use atomic.AddInt32/64

go run atomic.go
# counter: {count:2000}

Benchmark

Compare mutex increase and atomic increase.

bash ./test_benchmark.sh
benchkmark mutex
goos: darwin
goarch: amd64
BenchmarkMutexCounter-4          3000000               467 ns/op
PASS
ok      command-line-arguments  1.897s
benchkmark atomic
goos: darwin
goarch: amd64
BenchmarkAtomicCounter-4         3000000               487 ns/op
PASS
ok      command-line-arguments  1.954s