Grpc IdleTimeout Causing Goroutine Leakage

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Describe the bug

A critical issue has been discovered in the grpc implementation, specifically with regards to the IdleTimeout feature. When the IdleTimeout is set to 30 minutes, it causes a goroutine leakage in the etcd watch functionality. This bug can have severe consequences, including memory leaks and potential system crashes.

To Reproduce

Environment

  • Operating System: Linux
  • Framework: go-zero v1.6.0
  • Tool: goctl v1.6.0
  • grpc version: v1.64.0

Code

The code snippet responsible for the bug is located in the OnCallBegin function of the Manager struct. This function is called when a new RPC request is received. The relevant code is as follows:

func (m *Manager) OnCallBegin() error {
	if m.isClosed() {
		return nil
	}

	if atomic.AddInt32(&m.activeCallsCount, 1) > 0 {
		// Channel is not idle now. Set the activity bit and allow the call.
		atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
		return nil
	}

	// Channel is either in idle mode or is in the process of moving to idle
	// mode. Attempt to exit idle mode to allow this RPC.
	if err := m.ExitIdleMode(); err != nil {
		// Undo the increment to calls count, and return an error causing the
		// RPC to fail.
		atomic.AddInt32(&m.activeCallsCount, -1)
		return err
	}

	atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
	return nil
}

Error

When there are no RPC requests within 30 minutes, the requests will cause the leakage of the following two goroutines:

Image

Expected behavior

The expected behavior is that there should be no goroutine leakage when the IdleTimeout is set to 30 minutes.

Screenshots

No screenshots are available for this issue.

Environments (please complete the following information):

  • Operating System: Linux
  • Framework: go-zero v1.6.0
  • Tool: goctl v1.6.0
  • grpc version: v1.64.0

More description

The bug is caused by the way the OnCallBegin function handles the IdleTimeout feature. When the IdleTimeout is set to 30 minutes, the function does not properly clean up the goroutines that are responsible for watching the etcd cluster. As a result, these goroutines continue to run even after the IdleTimeout has expired, causing a memory leak.

To reproduce the bug, follow these steps:

  1. Set the IdleTimeout to 30 minutes using the grpc package.
  2. Create a new RPC request that will trigger the OnCallBegin function.
  3. Wait for 30 minutes without sending any new RPC requests.
  4. Observe the memory usage of the goroutines responsible for watching the etcd cluster.

The bug can be fixed by properly cleaning up the goroutines are responsible for watching the etcd cluster when the IdleTimeout expires. This can be achieved by adding a new function that will be called when the IdleTimeout expires, which will clean up the goroutines and prevent the memory leak.

Solution

To fix the bug, we need to add a new function that will be called when the IdleTimeout expires. This function will clean up the goroutines responsible for watching the etcd cluster and prevent the memory leak.

Here is an example of how the new function can be implemented:

func (m *Manager) OnIdleTimeout() {
	// Clean up the goroutines responsible for watching the etcd cluster
	m.exitIdleMode()
}

We also need to modify the OnCallBegin function to call the OnIdleTimeout function when the IdleTimeout expires:

func (m *Manager) OnCallBegin() error {
	if m.isClosed() {
		return nil
	}

	if atomic.AddInt32(&m.activeCallsCount, 1) > 0 {
		// Channel is not idle now. Set the activity bit and allow the call.
		atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
		return nil
	}

	// Channel is either in idle mode or is in the process of moving to idle
	// mode. Attempt to exit idle mode to allow this RPC.
	if err := m.ExitIdleMode(); err != nil {
		// Undo the increment to calls count, and return an error causing the
		// RPC to fail.
		atomic.AddInt32(&m.activeCallsCount, -1)
		return err
	}

	// Call the OnIdleTimeout function when the IdleTimeout expires
	if time.Since(m.lastTimerCheck) > 30*time.Minute {
		m.OnIdleTimeout()
	}

	atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
	return nil
}

Q: What is the grpc IdleTimeout feature?

A: The grpc IdleTimeout feature is a mechanism that allows you to set a timeout for idle connections. When a connection is idle for a specified period of time, it will be closed to prevent memory leaks and other issues.

Q: What is the bug in the grpc IdleTimeout feature?

A: The bug in the grpc IdleTimeout feature is that it causes a goroutine leakage when the IdleTimeout is set to 30 minutes. This means that the goroutines responsible for watching the etcd cluster will continue to run even after the IdleTimeout has expired, causing a memory leak.

Q: How can I reproduce the bug?

A: To reproduce the bug, follow these steps:

  1. Set the IdleTimeout to 30 minutes using the grpc package.
  2. Create a new RPC request that will trigger the OnCallBegin function.
  3. Wait for 30 minutes without sending any new RPC requests.
  4. Observe the memory usage of the goroutines responsible for watching the etcd cluster.

Q: What is the expected behavior of the grpc IdleTimeout feature?

A: The expected behavior of the grpc IdleTimeout feature is that there should be no goroutine leakage when the IdleTimeout is set to 30 minutes.

Q: How can I fix the bug?

A: To fix the bug, you need to add a new function that will be called when the IdleTimeout expires. This function will clean up the goroutines responsible for watching the etcd cluster and prevent the memory leak.

Here is an example of how the new function can be implemented:

func (m *Manager) OnIdleTimeout() {
	// Clean up the goroutines responsible for watching the etcd cluster
	m.exitIdleMode()
}

You also need to modify the OnCallBegin function to call the OnIdleTimeout function when the IdleTimeout expires:

func (m *Manager) OnCallBegin() error {
	if m.isClosed() {
		return nil
	}

	if atomic.AddInt32(&m.activeCallsCount, 1) > 0 {
		// Channel is not idle now. Set the activity bit and allow the call.
		atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
		return nil
	}

	// Channel is either in idle mode or is in the process of moving to idle
	// mode. Attempt to exit idle mode to allow this RPC.
	if err := m.ExitIdleMode(); err != nil {
		// Undo the increment to calls count, and return an error causing the
		// RPC to fail.
		atomic.AddInt32(&m.activeCallsCount, -1)
		return err
	}

	// Call the OnIdleTimeout function when the IdleTimeout expires
	if time.Since(m.lastTimerCheck) > 30*time.Minute {
		m.OnIdleTimeout()
	}

	atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
	return nil
}

Q: What are the benefits of fixing the bug?

A: Fixing the bug will prevent the memory leak and other issues caused by the goroutine leakage. will improve the overall performance and reliability of your system.

Q: How can I prevent the bug from occurring in the future?

A: To prevent the bug from occurring in the future, you can follow these best practices:

  • Always test your code thoroughly before deploying it to production.
  • Use tools like go test and go vet to catch errors and bugs early.
  • Follow the guidelines and recommendations provided by the grpc package.
  • Keep your code up to date with the latest versions of the grpc package.

By following these best practices, you can prevent the bug from occurring in the future and ensure that your system is reliable and efficient.