Let’s talk about the non-reentrant problem of golang locks

In concurrent programming in Go language, lock is a mechanism to ensure thread safety of shared resources. It blocks other threads from accessing shared resources until the thread releases the lock. However, in the Go language, locks are not reentrant, which means that within a locked code area, if you apply for the lock again, it will cause a deadlock.

To better understand this problem, let us look at an example:

var mutex sync.Mutex

func foo() {
    mutex.Lock()
    bar()
    mutex.Unlock()
}

func bar() {
    mutex.Lock()
    // some operations
    mutex.Unlock()
}

In the above code, the foo() function acquires the lock and executes bar() function, finally releases the lock. The bar() function acquires the lock internally, performs some operations, and finally releases the lock.

In this case, if the bar() function is called again during the execution of the foo() function, a deadlock will result. Because after acquiring the lock, the bar() function is blocked waiting for the foo() function to release the lock, while the foo() function is blocked waiting for The bar() function releases the lock. This situation is a deadlock caused by the non-reentrancy of the lock.

In order to solve this problem, we can use other mechanisms to replace locks. For example, use Channel. In the Go language, the channel can be used as a more flexible and safe concurrent programming mechanism, which can ensure the orderliness and thread safety of data. Unlike locks, channels will not be deadlocked because programmers can freely control the channel.

The following is a sample code that uses channels instead of locks:

var ch = make(chan int, 1)

func foo() {
    ch <- 1
    bar()
    <-ch
}

func bar() {
    ch <- 1
    // some operations
    <-ch
}

In the above code, we use channels instead of locks to ensure data synchronization and thread safety. The operations in the foo() function and the bar() function are the same as in the previous code example. However, in this code example, we send and receive two values ​​in the ch channel to represent operations on the shared resource. This ensures thread synchronization and security.

To sum up, locks in the Go language are not reentrant, which means that within a locked code area, you cannot apply for a lock again, otherwise it will cause a deadlock. In order to solve this problem, we can use other mechanisms to replace locks and ensure data synchronization and thread safety. Among them, channel is a more flexible and safe concurrent programming mechanism, which can effectively avoid deadlock and other problems.

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