How the Go language detects goroutine leaks in testing

Original link: How the Go language detects goroutine leaks in testing

foreword

Hello everyone, I am asong;

As we all know, gorourtinethe design of the Golanguage is the core component of the concurrent implementation of the language. It is easy to use, but it also encounters various incurable diseases. Among them, leakage goroutineis one of the serious diseases. pprofTo achieve the purpose, but these performance analysis tools are often used with the help of their auxiliary troubleshooting after problems occur. Is there a tool that can prevent problems before they occur? Of course, goleakhe is here. It is open sourced by the Uberteam and can be used to detect goroutineleaks. It can be combined with unit testing to prevent it from happening. Let's take a look at it in this article goleak.

goroutine leak

I don’t know if you have encountered goroutineleaks in your daily development. goroutineLeaks are actually goroutineblocking. These blocked ones goroutinewill survive until the end of the process, and the stack memory they occupy cannot be released, resulting in less and less available memory in the system. until it crashes! A brief summary of several common leak causes:

GoroutineThe internal logic enters an infinite loop and keeps occupying resources
GoroutineWhen mated channel/ mutexused, it has been blocked due to improper use
GoroutineThe logic inside waits for a long time, causing the Goroutinenumber to explode

Next we use the classic combination of Goroutine+ to show the leak;channelgoroutine

func GetData() {
	var ch chan struct{}
	go func() {
		<- ch
	}()
}

func main()  {
	defer func() {
		fmt.Println("goroutines: ", runtime.NumGoroutine())
	}()
	GetData()
	time.Sleep(2 * time.Second)
}
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This example is channelforgetting to initialize, and both read and write operations will cause blocking. If this method is to write a single test, it will not be able to detect the problem:

func TestGetData(t *testing.T) {
	GetData()
}
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operation result:

=== RUN   TestGetData
--- PASS: TestGetData (0.00s)
PASS
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The built-in test cannot be satisfied, so let's introduce goleakit to test it.

goals

github地址：github.com/uber-go/gol…

使用goleak主要关注两个方法即可：VerifyNone、VerifyTestMain，VerifyNone用于单一测试用例中测试，VerifyTestMain可以在TestMain中添加，可以减少对测试代码的入侵，举例如下：

使用VerifyNone:

func TestGetDataWithGoleak(t *testing.T) {
	defer goleak.VerifyNone(t)
	GetData()
}
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运行结果：

=== RUN   TestGetDataWithGoleak
    leaks.go:78: found unexpected goroutines:
        [Goroutine 35 in state chan receive (nil chan), with asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector.GetData.func1 on top of the stack:
        goroutine 35 [chan receive (nil chan)]:
        asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector.GetData.func1()
        	/Users/go/src/asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector/main.go:12 +0x1f
        created by asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector.GetData
        	/Users/go/src/asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector/main.go:11 +0x3c
        ]
--- FAIL: TestGetDataWithGoleak (0.45s)

FAIL

Process finished with the exit code 1
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通过运行结果看到具体发生goroutine泄漏的具体代码段；使用VerifyNone会对我们的测试代码有入侵，可以采用VerifyTestMain方法可以更快的集成到测试中：

func TestMain(m *testing.M) {
	goleak.VerifyTestMain(m)
}
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运行结果：

=== RUN   TestGetData
--- PASS: TestGetData (0.00s)
PASS
goleak: Errors on successful test run: found unexpected goroutines:
[Goroutine 5 in state chan receive (nil chan), with asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector.GetData.func1 on top of the stack:
goroutine 5 [chan receive (nil chan)]:
asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector.GetData.func1()
	/Users/go/src/asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector/main.go:12 +0x1f
created by asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector.GetData
	/Users/go/src/asong.cloud/Golang_Dream/code_demo/goroutine_oos_detector/main.go:11 +0x3c
]

Process finished with the exit code 1
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VerifyTestMain的运行结果与VerifyNone有一点不同，VerifyTestMain会先报告测试用例执行结果，然后报告泄漏分析，如果测试的用例中有多个goroutine泄漏，无法精确定位到发生泄漏的具体test，需要使用如下脚本进一步分析：

# Create a test binary which will be used to run each test individually
$ go test -c -o tests

# Run each test individually, printing "." for successful tests, or the test name
# for failing tests.
$ for test in $(go test -list . | grep -E "^(Test|Example)"); do ./tests -test.run "^$test\$" &>/dev/null && echo -n "." || echo -e "\n$test failed"; done
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这样会打印出具体哪个测试用例失败。

goleak实现原理

从VerifyNone入口，我们查看源代码，其调用了Find方法：

// Find looks for extra goroutines, and returns a descriptive error if
// any are found.
func Find(options ...Option) error {
  // 获取当前goroutine的ID
	cur := stack.Current().ID()

	opts := buildOpts(options...)
	var stacks []stack.Stack
	retry := true
	for i := 0; retry; i++ {
    // 过滤无用的goroutine
		stacks = filterStacks(stack.All(), cur, opts)

		if len(stacks) == 0 {
			return nil
		}
		retry = opts.retry(i)
	}

	return fmt.Errorf("found unexpected goroutines:\n%s", stacks)
}
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我们在看一下filterStacks方法：

// filterStacks will filter any stacks excluded by the given opts.
// filterStacks modifies the passed in stacks slice.
func filterStacks(stacks []stack.Stack, skipID int, opts *opts) []stack.Stack {
	filtered := stacks[:0]
	for _, stack := range stacks {
		// Always skip the running goroutine.
		if stack.ID() == skipID {
			continue
		}
		// Run any default or user-specified filters.
		if opts.filter(stack) {
			continue
		}
		filtered = append(filtered, stack)
	}
	return filtered
}
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这里主要是过滤掉一些不参与检测的goroutine stack，如果没有自定义filters，则使用默认的filters：

func buildOpts(options ...Option) *opts {
	opts := &opts{
		maxRetries: _defaultRetries,
		maxSleep:   100 * time.Millisecond,
	}
	opts.filters = append(opts.filters,
		isTestStack,
		isSyscallStack,
		isStdLibStack,
		isTraceStack,
	)
	for _, option := range options {
		option.apply(opts)
	}
	return opts
}
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从这里可以看出，默认检测20次，每次默认间隔100ms；添加默认filters;

总结一下goleak的实现原理：

Use the runtime.Stack()method to obtain all the stack information currently running goroutine. By default, the filter items that do not need to be detected are defined by default. The number of detections + detection interval is defined by default, and the detection is performed periodically. Finally, after multiple checks, the remaining ones are not found, and goroutinethen it is judged that there is no goroutineleak . .

Summarize

In this article, we share a tool that can find goroutineleaks in testing, but it still needs complete test case support, which exposes the importance of test cases. Friends, good tools can help us find problems faster, but code The quality is still in our own hands, come on, boys~.

Well, this article ends here, I'm asong , see you next time.

Welcome to the public account: Golang Dream Factory

References