Discuss how Golang prohibits instruction reordering

With the continuous advancement of the computer field, programming languages ​​are also constantly updated and improved. Go language (also known as Golang), as a programming language that has emerged in recent years, has the characteristics of efficiency and simplicity, and has been favored by more and more developers. When using Golang for multi-threaded programming, avoiding instruction rearrangement is a very important issue. This article will discuss in detail Golang's method of prohibiting instruction reordering.

1. What is instruction rearrangement

In a computer, the instruction executed by the CPU consists of several parts, including instruction fetching, decoding, execution, memory access and write back. Instruction rearrangement means that when the CPU executes instructions, it may optimize and adjust the instructions based on current conditions, data, etc., to achieve better execution results. At this time, there will be a situation where the order of instruction execution is inconsistent with the order of code writing, which is instruction rearrangement.

The existence of instruction rearrangement is helpful to improve the execution efficiency of the CPU, but for multi-threaded programming, instruction rearrangement may lead to data inconsistency and abnormal program behavior.

2. Problems caused by instruction rearrangement

Instruction rearrangement will cause many problems. For example, when a thread reads a variable without modifying the variable, the value of the variable will be different at different times. If another thread reads the same variable before one thread modifies it, then that thread sees inconsistent values ​​for the variable and produces incorrect results in subsequent calculations.

In more extreme cases, instruction rearrangement may cause abnormal behavior of the program, such as deadlock, infinite loop, etc. For example, in a multi-threaded program, a thread A waits for other threads to write the value of variable X, and thread B modifies the value of variable Y before writing X. It is possible that thread A waits indefinitely because it obtains an inconsistent Y value. At this time, thread B can continue execution because it obtains the latest Y value.

3. Methods to prohibit instruction rearrangement

In order to avoid instruction rearrangement, the following methods are usually used:

1. Use locks

Lock The mechanism is an inefficient but powerful way. The lock mechanism can force the CPU to execute the code in the order to avoid instruction rearrangement. Mutex (mutex lock) in golang is a lock mechanism that consists of a mutex, a waiter queue and two pointers.

2. Use atomic operations

Atomic operations are uninterruptible operations, which can ensure the integrity and indivisibility of the operation. Once execution is started, it will continue to be executed without being interrupted. , and will not overlap with other operations. Golang provides some atomic operation functions, such as AddInt32, SwapInt32, etc. These functions can ensure that instructions will not be rearranged during multi-thread execution.

3. Use the synchronization mechanism

The synchronization mechanism refers to using mechanisms such as Channel or WaitGroup to achieve synchronization to avoid data inconsistency caused by instruction rearrangement. Channel is a communication mechanism provided in golang, which can realize synchronization and communication between threads. WaitGroup is an auxiliary type in golang, used to wait for the end of a group of threads.

4. Summary

In multi-threaded programming, the problem of instruction rearrangement is a problem that needs to be taken seriously. Instruction reordering can lead to data inconsistencies and unexpected program behavior. In order to avoid instruction rearrangement, golang provides a variety of methods, such as using locks, atomic operations, and synchronization mechanisms. In actual programming, appropriate methods can be selected and adjusted according to specific needs and situations to achieve better execution results and data accuracy.

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