What does it mean when go's CompareAndSwap returns false?

#php editor Baicao will introduce today about the CompareAndSwap function in Go language. In the Go language, the CompareAndSwap function is mainly used for atomic operations to compare and exchange two values. When the CompareAndSwap function returns false, it means that the comparison and swap operation was not performed successfully, that is, the new value does not match the old value. This may be due to other goroutines modifying the value of the variable at the same time, or the value of the variable having been modified. Understanding this is important for writing concurrency-safe code and can help us avoid potential race conditions and data inconsistencies.

Question content

There are many atomic operations in Go source code. For example, sync.Map uses a large number of atomic operations, such as CompareAndSwap, and CompareAndSwap returns a bool type value to indicate whether it is successful. Returns true if successful, false otherwise. I have some questions about this method:

1. If the compared values ​​are not equal, does CompareAndSwap return false?
2. Will CompareAndSwap fail if the comparison values ​​are equal?

Solution

As the documentation states, compareandswap is equivalent to:

if *addr == old {
    *addr = new
    return true
}
return false

Therefore, if the values ​​are not equal, false is returned and the swap operation does not occur. This is useful for determining if some value has changed since it was last set, and if it hasn't, set it to a different value.

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