How to profile number of goroutines

go profiling pprof
tommy_p1ckles picture tommy_p1ckles · Jul 15, 2016 · Viewed 12.1k times · Source

Basically I want to find if my program is leaking goroutines over time. So I want to see how many goroutines are running over time. Is there any way to do this through pprof?

I've done go tool pprof http://localhost:8888/debug/pprof/block.

Which gives me how long is being spent blocked but not how many routines are running.

Answer

user1431317 picture user1431317 · Jul 16, 2016

Open http://localhost:8888/debug/pprof/ in your browser. You'll see two relevant links: "goroutine" (http://localhost:8888/debug/pprof/goroutine?debug=1) and "full goroutine stack dump" (http://localhost:8888/debug/pprof/goroutine?debug=2).

The first one will show all goroutines that share the same code as one entry, with the number of such goroutines before their name. For example:

1 @ 0x42f223 0x42f2e4 0x40542f 0x404f4b 0x4a0586 0x4600a1
#   0x4a0586    gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands.(*RunCommand).startWorkers+0x56   /home/me/go/src/gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands/multi.go:164

1 @ 0x42f223 0x43dfd7 0x43d532 0x4a04ed 0x4600a1
#   0x4a04ed    gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands.(*RunCommand).processRunners+0x45d    /home/me/go/src/gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands/multi.go:147

There's one of both of these goroutines, that's what the 1 before the @ means.

The full dump is extremely useful for finding leaks, it'll show you every goroutine separately, as well as its stack trace and what it's doing (e.g. how long it has been waiting to receive from a channel):

goroutine 49 [chan receive, 2 minutes]:
gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands.(*RunCommand).startWorkers(0xc820103ee0, 0xc820274000, 0xc820274060, 0xc8201d65a0)
    /home/me/go/src/gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands/multi.go:164 +0x56
created by gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands.(*RunCommand).Run
    /home/me/go/src/gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands/multi.go:294 +0x41b

goroutine 50 [select]:
gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands.(*RunCommand).processRunners(0xc820103ee0, 0x0, 0xc820274060, 0xc8201d65a0)
    /home/me/go/src/gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands/multi.go:147 +0x45d
created by gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands.(*RunCommand).startWorkers
    /home/me/go/src/gitlab.com/gitlab-org/gitlab-ci-multi-runner/commands/multi.go:165 +0x96

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