An example to show string is not thread safe.
b
05
b
b
b
b
b
b
b
b
go tool compile -S -S main.go
...
rel 5+4 t=17 TLS+0
rel 49+4 t=8 time.Sleep+0
rel 75+4 t=16 "".a+4
rel 85+4 t=16 runtime.writeBarrier+-1
rel 95+4 t=16 go.string."0"+0
rel 102+4 t=16 "".a+0
rel 111+4 t=16 "".a+0
rel 118+4 t=16 go.string."0"+0
rel 123+4 t=8 runtime.gcWriteBarrierCX+0
rel 133+4 t=16 "".a+4
rel 143+4 t=16 runtime.writeBarrier+-1
rel 153+4 t=16 go.string."bb"+0
rel 160+4 t=16 "".a+0
rel 169+4 t=16 "".a+0
rel 176+4 t=16 go.string."bb"+0
rel 181+4 t=8 runtime.gcWriteBarrierCX+0
rel 193+4 t=8 runtime.morestack_noctxt+0
...