1つのスレッドで「イベント」構造体を生成し、数秒間隔でメインスレッドに送り返しています。当然、それは正しく機能しません。2つの質問があります：
- 選択ループで何億ものイベント受信メッセージを受け取るのはなぜですか？ファイル記述子がそこに何かがあると言わないように、パイプから読み取る必要がありますか？
- 構造体への参照をパイプから引き出すにはどうすればよいですか？
必要な出力：
$ ...
Writing event 1 to pipe
Received event on pipe
Writing event 2 to pipe
Received event on pipe
実際の出力：
$ ...
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event on pipe
Received event o^C
GCCコマンド：
gcc -o test test.c
test.c：
/* Simple example with two threads and a pipe. One thread writes structs to a
pipe every few seconds; the other reads the structs, prints out their info
and then frees the structs
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/select.h>
void mywait(int timeInSec);
// The events
typedef struct event {
int id;
int data;
} event_t;
int id = 0;
int pipefd[2];
void* pump(void *arg) { // Generates events
for (;;)
{
mywait(1); // sleep thread
printf("writing event #%i to pipe\n", id);
// generate event
event_t *event;
event = malloc(sizeof(*event));
memset(event, 0, sizeof(*event));
event->id = id++;
// write event to pipe
write(pipefd[1], &event, sizeof(event));
// NOTE: Free event in other thread
}
}
int main (int argc, char **argv)
{
printf("Starting pipe_test.c\n");
// 1. Create a pipe
pipe(pipefd);
// 2. Create thread to pump events into pipe
pthread_t tid;
if (pthread_create( &tid, NULL, pump, NULL) != 0) {
perror("pthread_create:pump");
exit(-1);
}
// 3. Set up selector in main thread to read events off pipe
int z;
fd_set readfds; //readable file descriptor
int selectmax;
selectmax = pipefd[0] + 1;
for (;;)
{
// Initialize selector
FD_ZERO( &readfds );
FD_SET( pipefd[0], &readfds );
z = select( selectmax, &readfds, NULL, NULL, NULL );
if( z < 0 ) {
printf( "select() failed\n");
// close( pipefd ); //???
return 1;
} else {
if( FD_ISSET( pipefd[0], &readfds ) ) {
printf("Received event on pipe\n"); // I get a shitton of these
// Get the pointer to the event struct from the pipe
// TODO: GOOD WAY TO DO THIS?
// Free the struct
// TODO
}
}
}
return 0;
}
// From http://somethingswhichidintknow.blogspot.com/2009/09/sleep-in-pthread.html
pthread_mutex_t fakeMutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t fakeCond = PTHREAD_COND_INITIALIZER;
void mywait(int timeInSec)
{
struct timespec timeToWait;
struct timeval now;
int rt;
gettimeofday(&now,NULL);
timeToWait.tv_sec = now.tv_sec + timeInSec;
timeToWait.tv_nsec = now.tv_usec*1000;
pthread_mutex_lock(&fakeMutex);
rt = pthread_cond_timedwait(&fakeCond, &fakeMutex, &timeToWait);
pthread_mutex_unlock(&fakeMutex);
}