Multi-threading interview FAQs in C++

C is a powerful programming language and one of the important languages ​​for developing multi-threaded applications. Nowadays, more and more companies are beginning to regard multi-threaded programming as an important inspection point in interviews. This article will summarize and answer common questions in C multi-threading interviews.

1. What is a thread? What is the difference between thread and process?

Thread refers to the smallest unit when a computer executes a program concurrently. A process can have multiple threads, and a process is a running application instance. Threads can share data and resources in the process, which is a lightweight concurrency method. Compared with processes, threads are faster to create, cancel, and switch, and they also occupy less system resources.

The main difference between processes and threads is that the former has independent address space and system resources, while the latter shares these resources. Creating multiple threads in a process allows each thread to cooperate with each other to achieve more efficient concurrent task processing.

2. How to create a thread?

In C, you can use the std::thread class to create a new thread. The specific method is: define a function, and then use std::thread to create a thread. For example:

void task1(){
  // do something…
}

int main(){
  std::thread t1(task1);  // 创建一个新线程
  t1.join();  // 等待线程执行结束
  return 0;
}

When creating a new thread, you need to pay attention to the data and resources shared between different threads, and you need to correctly manage the mutual exclusion and synchronization between threads.

3. What is thread safety?

Thread safety refers to ensuring the correctness of access and modification of shared data in each thread in a multi-threaded program. Thread safety can be achieved by locking, using atomic operations, and avoiding shared data.

In C, there are many standard library functions and data structures that are thread-safe and can be used directly in multi-threaded programs. At the same time, you also need to pay attention to using mechanisms such as mutex locks and condition variables to ensure that the code you write is also thread-safe.

4. What is a deadlock? How to avoid deadlock?

Deadlock refers to a situation where two or more threads are waiting for each other's resources, causing the program to be unable to continue execution. A common deadlock scenario is that two threads try to acquire the lock occupied by each other, causing each other to be unable to execute.

To avoid deadlock, you need to ensure that when accessing shared resources, the correct locking sequence is used to ensure that all threads acquire locks in the same order. At the same time, you can use the timeout mechanism to proactively give up the current lock when waiting for the resource occupied by the other party to avoid deadlock.

5. What is a mutex lock? How to use mutex lock?

Mutex lock is a common mechanism to protect shared data in a multi-threaded environment. It implements a mechanism whereby when one thread occupies shared data, other threads need to wait for the mutex lock to be released before they can access the data.

In C, you can use the std::mutex class to implement a mutex lock. For example:

#include <mutex>
#include <thread>
#include <iostream>

std::mutex mtx;  // 定义一个互斥锁

void task1(){
  std::lock_guard<std::mutex> lock(mtx);  // 定义一个锁，保护共享数据
  // do something…
}

int main(){
  std::thread t1(task1);
  t1.join();
  return 0;
}

When using a mutex, you need to pay attention to the access sequence of different threads and the granularity of the lock to avoid deadlocks or performance bottlenecks.

The above is a summary and answers to common questions in C multi-threading interviews. In the actual interview, in addition to technical questions, you also need to show good teamwork spirit and problem-solving ideas and abilities. I hope this article can help prepare for C multi-threading interviews.

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