void setSemaphore(QSemaphore& sem) { semaphore = sem; } private: QSemaphore semaphore; };为什么报错
时间: 2024-06-03 14:08:33 浏览: 9
*s, int value) {
s->release(value);
}
This function takes a pointer to a QSemaphore object and an integer value as parameters. It then sets the value of the semaphore to the specified value by calling the QSemaphore method 'release'. The 'release' method increases the value of the semaphore by the specified amount, allowing threads to acquire the semaphore.
相关问题
void setSemaphore(QSemaphore& sem) { semaphore = sem; } private: QSemaphore semaphore; };semaphore = sem为什么报错
QSemaphore is a class in the Qt framework that provides a way for threads to communicate with each other by controlling access to resources. A semaphore can be thought of as a counter that is used to limit the number of threads that can access a shared resource at the same time.
To set a semaphore, you need to create an instance of the QSemaphore class and initialize it with a value that represents the number of threads that are allowed to access the resource simultaneously. Here's an example:
```
QSemaphore semaphore(2); // Allow two threads to access the resource at the same time
```
In this example, we create a semaphore with an initial value of 2, which means that two threads can access the resource at the same time. If more than two threads try to access the resource simultaneously, the extra threads will have to wait until one of the existing threads releases the semaphore.
Once you have created a semaphore, you can use it in your code to control access to shared resources. For example, here's how you might use a semaphore to limit the number of threads that can write to a file:
```
void writeToFile(QFile& file, const QString& data, QSemaphore& semaphore)
{
semaphore.acquire(); // Wait for permission to access the file
QTextStream stream(&file);
stream << data << endl;
semaphore.release(); // Release the semaphore to allow other threads to access the file
}
```
In this example, the writeToFile function takes a QFile object, a QString containing the data to write, and a QSemaphore object. The function first calls the acquire method on the semaphore to wait for permission to access the file. Once permission is granted, the function writes the data to the file and then releases the semaphore using the release method to allow other threads to access the file.
Overall, using semaphores can help you ensure that your code is thread-safe and that multiple threads can access shared resources without causing conflicts or race conditions.
Line 4: Char 5: error: unknown type name 'sem_t' sem_t zero_sem;
对不起,我之前给出的修正代码中使用了信号量,但是在C++标准库中并没有直接提供信号量的支持。
如果您想要使用信号量,您需要使用操作系统提供的信号量实现,比如在POSIX标准中定义的信号量。您可以使用`sem_init()`、`sem_wait()`和`sem_post()`等函数来操作信号量。
以下是使用POSIX信号量实现的修正代码:
```cpp
#include <iostream>
#include <functional>
#include <mutex>
#include <condition_variable>
#include <semaphore.h>
class ZeroEvenOdd {
private:
int n;
sem_t zero_sem;
sem_t even_sem;
sem_t odd_sem;
public:
ZeroEvenOdd(int n) {
this->n = n;
sem_init(&zero_sem, 0, 1);
sem_init(&even_sem, 0, 0);
sem_init(&odd_sem, 0, 0);
}
~ZeroEvenOdd() {
sem_destroy(&zero_sem);
sem_destroy(&even_sem);
sem_destroy(&odd_sem);
}
void zero(std::function<void(int)> printNumber) {
for (int i = 0; i < n; i++) {
sem_wait(&zero_sem);
printNumber(0);
if (i % 2 == 0) {
sem_post(&odd_sem);
} else {
sem_post(&even_sem);
}
}
}
void even(std::function<void(int)> printNumber) {
for (int i = 2; i <= n; i += 2) {
sem_wait(&even_sem);
printNumber(i);
sem_post(&zero_sem);
}
}
void odd(std::function<void(int)> printNumber) {
for (int i = 1; i <= n; i += 2) {
sem_wait(&odd_sem);
printNumber(i);
sem_post(&zero_sem);
}
}
};
```
请确保在编译和运行代码时链接了`-lpthread`选项,以便正确使用POSIX信号量。
相关推荐
![rar](https://img-home.csdnimg.cn/images/20210720083606.png)
![rar](https://img-home.csdnimg.cn/images/20210720083606.png)
![pdf](https://img-home.csdnimg.cn/images/20210720083512.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)
![](https://csdnimg.cn/download_wenku/file_type_ask_c1.png)