Lock contention and lock solutions in C++

With the continuous development of the computer field and the growing application requirements, multi-thread programming has become an indispensable technical means. In the process of multi-threaded programming, lock competition is often encountered. Lock competition is caused by multiple threads competing for the same lock. In a high-concurrency environment, it can lead to program performance degradation, deadlock and other problems. This article will introduce the lock contention problem in C and its solution.

1. Lock competition issue

In multi-threaded programming, locks are a technical means to achieve thread synchronization and are used to ensure the order in which multiple threads access shared resources. . In code, when using locks, they are usually encapsulated using STL containers such as std::mutex or std::lock_guard to avoid omissions when manually operating locks.

However, locks can also cause some problems, the most common of which is lock contention. Lock competition occurs when multiple threads compete for the same lock resource, which may cause performance problems or deadlock problems in the program.

The problem of lock competition can be solved through the following solutions:

2. Lock-free competition solution

The lock-free competition solution refers to the lock-free competition solution. Design algorithms or data structures to avoid the use of locks, thereby achieving the purpose of avoiding lock competition. The advantage of this solution is that it can avoid performance problems caused by lock competition. However, the lock-free competition solution is more difficult to implement, the amount of code is relatively large, and it also has certain requirements on the programmer's ability and experience.

3. Loop waiting competition scheme

Loop waiting competition scheme means that when a thread requests a lock, if the lock is already occupied by other threads, it will wait until The lock is released. The advantage of this solution is that it can solve the problem of lock competition, but it will cause deadlock problems.

4. Recursive lock scheme

The recursive lock scheme means that when a thread requests a lock, if the thread already owns the lock resource, it does not need to wait and directly enters the critical section. Can. The advantage of this solution is that it is simple and easy to use and can avoid deadlock problems.

5. Read-write lock scheme

Read-write lock scheme refers to distinguishing lock resources between reading and writing through read-write locks. Read locks and write locks can exist at the same time, but Only one thread can perform write operations at the same time. The advantage of this solution is that it can improve the performance of read operations, but it needs to be selected based on specific application scenarios.

6. Summary

Lock competition is a common problem in multi-threaded programming and will affect the performance and stability of the program. For this problem, we can deal with it by choosing appropriate locks and lock contention solutions. In the actual programming process, selection needs to be made based on specific application scenarios to minimize the impact of lock competition on program performance.

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