[英]Race Condition with fork() and pipe()
我正在编写一个程序,其中有一个父级游戏针对N个子进程连接四个。 该程序使用管道在进程之间传递游戏动作。
但是,我在解决程序中存在的竞争条件时遇到问题。 游戏结束后,子进程会挂起其read()调用。 这似乎仅在有多个子进程时才发生。
我已经尝试了几种方法,例如命名信号量,但是对于fork,pipe和IPC还是很陌生。 我在这里发布了带有相关代码的要点(为了可读性,我尽力将其清理得最好):
任何帮助将不胜感激
编辑
这是要点的相关来源,其中添加了声明。
int main (int argc, char const *argv[])
{
int dimension = 8, children = 2, i;
int child_play_to_win = 0;
int fd[children][4];
pid_t childpid[children];
Board** boards = (Board**) malloc(sizeof(Board*) * children);
GameMove* lastMove, *tmpMove;
char buf[80];
for(i = 0; i < children; i++) {
generate_board(&(boards[i]), dimension);
int tmp[2];
pipe(tmp);
// child read
fd[i][0] = dup(tmp[0]);
// parent write
fd[i][1] = dup(tmp[1]);
pipe(tmp);
// parent read
fd[i][2] = dup(tmp[0]);
// child write
fd[i][3] = dup(tmp[1]);
childpid[i] = fork();
if(childpid[i] == -1) {
perror("fork");
exit(1);
}
if(childpid[i] == 0) {
srand(getpid());
close(fd[i][1]);
close(fd[i][2]);
while(!boards[i]->finished) {
// Read in move from parent
printf("child[%d] about to read\n", getpid());
read(fd[i][0], &buf, sizeof(GameMove));
// repeat parent move on this board
if(gameNotFinished) {
// make child move
// write move back to parent
write(fd[i][3], lastMove, sizeof(GameMove));
// If the board is finished (there was a win),
if (!gameNotFinihsed) {
// Child wins
close(fd[i][0]);
close(fd[i][3]);
printf("child[%d] ending\n", getpid());
break;
}
}
else {
// Parent won
close(fd[i][0]);
close(fd[i][3]);
break;
}
}
dealloc(boards[i]);
exit(0);
}
}
// When this hits children amount, all games are done
int games_complete = 0;
// Make first move to all children
for (i = 0; i < children; i++) {
close(fd[i][0]);
close(fd[i][3]);
lastMove = placePieceAtBestPosition(boards[i], 1);
printf("parent writing to child[%d]\n", childpid[i]);
write(fd[i][1], lastMove, sizeof(GameMove));
}
while (games_complete != children) {
for (i = 0; i < children; i++) {
// Read move from child
read(fd[i][2], &buf, sizeof(GameMove));
// repeat child move
// Check for a child win...
if (!checkForWin(boards[i], 2)) {
// No win yet, place piece at best position
lastMove = placePieceAtBestPosition(boards[i], 1);
// check for win again
boards[i]->finished = checkForWin(boards[i], 1);
// Write move back to child
write(fd[i][1], lastMove, sizeof(GameMove));
// If we won, close everything up and increment
// the games_complete counter.
if(boards[i]->finished) {
close(fd[i][1]);
close(fd[i][2]);
games_complete++;
}
} else {
// write back child move if there was a win
write(fd[i][1], lastMove, sizeof(GameMove));
close(fd[i][1]);
close(fd[i][2]);
printf("Parent lost! ):\n");
games_complete++;
}
}
}
我想我知道你的问题是什么。 派生每个孩子时,请关闭其管道的父级。 但是,每个孩子仍然为所有先前的孩子打开管道的父侧。 因此,只有最后创建的子项才会关闭其父级管道。
建议您更改:
close(fd[i][1]);
close(fd[i][2]);
像这样:
for (j = 0; j <=i; j++) {
close(fd[j][1]);
close(fd[j][2]);
}
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