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我有一个在程序开始时启动的后台进程，它每 20 毫秒生成一次输出数据。在我的程序中，我想读取这些数据，但想避免不断地写入/读取文件，因为这可能非常慢。

每次迭代的输出都是一个字符串（最大长度约 100 个字符），我只需要任何给定时间的最新数据。

理想情况下，我可以使用某种内存缓冲区来获取这些数据，但我不确定如何执行此操作。我已经研究过使用 popen （另请参见：c++: subprocess output to stdin），但是，这似乎用于执行命令，并等待单个输出。我的输出或多或少会不断变化。我在Raspbian上运行这个程序。

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2 回答 2

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我认为您想将标准输出重定向到字符串流。它在这里描述。

结合这一项。

现在您已经重定向了标准输出，并且能够将其发送到另一个进程。

于 2013-03-07T04:53:52.947 回答
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使用共享内存：为要共享的数据分配内存，并为互斥变量分配第二个段以处理锁定。

共享 float[9] 的示例代码：

服务器

int shmid, shmid_mutex;
key_t key = 1337, key_mutex = 1338;
float *shm;
pthread_mutex_t *shm_mutex;
int SHMSZ = sizeof(float[9]), SHMSZ_mutex = sizeof(pthread_mutex_t);

//Mutex shared memory
shmid_mutex = shmget(key_mutex, SHMSZ_mutex, IPC_CREAT | 0660); //Create the segment
shm_mutex = (pthread_mutex_t *)shmat(shmid_mutex, NULL, 0); //Attach the segment to data space
shmctl(shmid_mutex, SHM_LOCK, (struct shmid_ds *) NULL); //Lock this segment from being swapped

//Setup mutex attributes
pthread_mutexattr_t psharedm;
pthread_mutexattr_init(&psharedm);
pthread_mutexattr_setpshared(&psharedm, PTHREAD_PROCESS_SHARED);
//Initialize mutex
pthread_mutex_init(shm_mutex, &psharedm);

//Float array shared memory
shmid = shmget(key, SHMSZ, IPC_CREAT | 0660); //Create the segment
shm = (float *)shmat(shmid, NULL, 0); //Attach the segment to data space
shmctl(shmid, SHM_LOCK, (struct shmid_ds *) NULL); //Lock this segment from being swapped

float x = 0.1;
while(true)
{
    pthread_mutex_lock(shm_mutex); //start critical section
    //Write to shared memory
    for (int i = 0; i < 9; i++)
        shm[i] = x * i;
    x += 0.1;
    printf("W ");
    for (int i = 0; i < 9; i++)
        printf("%f ", shm[i]);
    printf("\n");
    usleep(100000); //slow down output to make it readable
    pthread_mutex_unlock(shm_mutex);  //end critical section
    usleep(10000); //wait for 10ms to simulate other calculations
}

客户

int shmid, shmid_mutex;
key_t key = 1337, key_mutex = 1338;
float *shm;
pthread_mutex_t *shm_mutex;
int SHMSZ = sizeof(float[9]), SHMSZ_mutex = sizeof(pthread_mutex_t);

//Mutex shared memory
shmid_mutex = shmget(key_mutex, SHMSZ_mutex, IPC_CREAT | 0660); //Create the segment
shm_mutex = (pthread_mutex_t *)shmat(shmid_mutex, NULL, 0); //Attach the segment to data space
shmctl(shmid_mutex, SHM_LOCK, (struct shmid_ds *) NULL); //Lock this segment from being swapped

//Float array shared memory
shmid = shmget(key, SHMSZ, 0660); //Locate the segment
shm = (float *)shmat(shmid, NULL, 0); //Attach the segment to data space
shmctl(shmid, SHM_LOCK, (struct shmid_ds *) NULL); //Lock this segment from being swapped

while(true)
{
    pthread_mutex_lock(shm_mutex); //start critical section
    //Read from shared memory
    printf("R ");
    for (int i = 0; i < 9; i++)
        printf("%f ", shm[i]);
    printf("\n");
    usleep(100000); //slow down output to make it readable
    pthread_mutex_unlock(shm_mutex); //end critical section
    usleep(10000); //wait for 10ms to simulate other calculations
}
于 2013-04-01T15:48:25.780 回答