What is race condition in C++ multi-threaded programming?

Race Condition Overview When multiple threads access shared resources, a Race Condition will occur in an unpredictable order, resulting in unpredictable program behavior. Detect Race Conditions using thread analysis tools such as Valgrind. Add assertions and logs to check expected values ​​of shared resources. To solve the Race Condition, use a mutex (Mutex) to ensure exclusive access to shared resources. Use read-write lock (ReadWriteLock) to allow concurrent read operations. Use atomic variables for predictable access order.

Race Condition in C++ multi-threaded programming

Race Condition Overview

Race condition, also known as race condition Speed ​​condition is a common phenomenon in parallel programming. A race condition occurs when multiple threads access a shared resource simultaneously and in an unpredictable order. This can cause the program to behave unexpectedly or even crash.

How to detect Race Condition

Detecting race condition is not easy because it only occurs under certain conditions. Some common diagnostic methods include:

• Thread analysis tools: Such as Valgrind or ThreadSanitizer, which can detect data races and other threading issues.
• Assertions and Logging: Check expected values ​​for shared resources and log exceptions when they occur.

Practical case

The following is a C++ code example showing race condition:

#include <iostream>
#include <thread>

using namespace std;

int shared_resource = 0;

void increment_resource() {
  for (int i = 0; i < 1000000; i++) {
    shared_resource++;
  }
}

int main() {
  thread t1(increment_resource);
  thread t2(increment_resource);

  t1.join();
  t2.join();

  cout << "Expected value: 2000000, Actual value: " << shared_resource << endl;
  return 0;
}

In this example, two threads run simultaneously Update shared resource shared_resource. Due to the uncertain order of thread execution, the final value may be less than 2000000.

Solving Race Condition

The key to solving race condition is to synchronize access to shared resources. There are several synchronization mechanisms to choose from:

• Mutex (Mutex): Allows one thread to have exclusive access to a shared resource.
• ReadWriteLock (ReadWriteLock): Allows multiple threads to read shared resources concurrently, but only one thread can write.
• Atomic variables: Provides a series of atomic operations, such as atomic increment and comparison exchange.

By correctly using these synchronization mechanisms, you can ensure that access to shared resources occurs in a predictable order, thereby eliminating race conditions.

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