How Do Go Goroutines Maintain Concurrency When One Is Blocked on a System Call?

Goroutines and OS Threads: Achieving Concurrency in Go

In Go, goroutines provide a lightweight mechanism for concurrent programming. Unlike threads in other programming languages, goroutines do not have a one-to-one mapping to operating system (OS) threads. This raises the question: how can goroutines continue executing while one of them is blocked on a system call?

Goroutine Execution Model

Go's documentation explains that goroutines are multiplexed onto a pool of OS threads. This means that multiple goroutines share the same underlying thread. When a goroutine makes a blocking syscall, such as waiting for I/O, the thread it's running on becomes blocked as well.

How Go Handles Blocking Syscalls

The Go runtime manages this situation by creating a new OS thread to handle the blocked goroutine. This new thread takes over the blocking operation, freeing up the original thread to continue executing other goroutines.

Example

Consider the following scenario with GOMAXPROCS=1, which limits the number of OS threads to 1:

go func() {
  // Perform a blocking syscall (e.g., file I/O)
  time.Sleep(5 * time.Second)
}

// Other goroutines continue executing here
for {
  log.Println("Non-blocking loop")
}

In this example, when the first goroutine blocks on the Sleep syscall, the Go runtime will launch a new OS thread to handle the blocking operation. Meanwhile, the other goroutine(s) can continue executing on the original OS thread since it is no longer blocked.

Conclusion

The ability to multiplex goroutines onto a pool of OS threads allows Go to maintain concurrency even when some goroutines are blocked on system calls. By creating new OS threads as needed, Go ensures that other goroutines can continue executing without being affected by blocking operations.

The above is the detailed content of How Do Go Goroutines Maintain Concurrency When One Is Blocked on a System Call?. For more information, please follow other related articles on the PHP Chinese website!