我是这种编程的新手，所以如果这是一个转储问题，我很抱歉。我正在尝试做一个非常简单的任务，但我似乎不明白出了什么问题。
我有一个创建多个子进程的父进程，并且通过使用 FIFO 我想向所有子进程发送消息（例如“hi”），进程接收到消息，但是有无论我做什么，都会出现错误，而且似乎无法找到问题所在。
这是父级的主要功能：
ERR_CONNECTION_REFUSED localhost refused to connect.
这是我保存每个进程信息的类：
int main(int argc, char *argv[])
{
int num_monitors, buf_size; //command line arguments
num_monitors = stoi(argv[1]);
buf_size = stoi(argv[2]);
// Structures to store monitor info
Monitors *m_info = new Monitors[num_monitors]; // Stores monitor pid & pipe ends
create_n_monitors(m_info,num_monitors,buf_size,input_dir_path);
sleep(1); // making sure all pipes get created
for(int i=0; i<num_monitors; i++) // opening the write end now that the monitors have been created
{
m_info[i].write_fd = open(m_info[i].write_p, O_WRONLY | O_NONBLOCK);
if (m_info[i].write_fd == -1){perror("open @ 27 main parent");exit(1);}
}
for(int i=0; i<num_monitors; i++)
send_message(m_info[i].write_fd, (char*)"hi", buf_size);
delete [] m_info;
return 0;
}
这是我如何创建进程和管道（FIFO）：
class Monitors
{
public:
pid_t m_pid; // monitors's PID
char read_p[32]; // write monitor - read parent pipe name
char write_p[32]; // read monitor - write parent pipe name
int read_fd; // file descriptor for read fifo of monitor
int write_fd; // file descriptor for write fifo of monitor
Monitors();
~Monitors();
};
最后是进程的主要功能：
void create_n_monitors(Monitors *m_info, int num_monitors, int buf_size, char *input_dir)
{
create_unique_fifo(true, NULL, 0); // creates a fifo file
for (int i = 0; i < num_monitors; ++i) // create num monitors
create_monitor(m_info, i, buf_size, input_dir);
}
/* ========================================================================= */
// Create a monitor and it's named fifos. Store it's info in <m_info[index]>.
void create_monitor(Monitors *m_info, int index, int buf_size, char *input_dir)
{
create_unique_fifo(false, m_info, index); // Create fifos
pid_t pid = fork();
if(pid == -1) {
perror("fork");
exit(1);
}
else if ( pid == 0) { // we are in the child monitor, read_p(read parent) : monitor's write end of the fifo
// write_p(write parent): monitor's read end
char buf_size_str[15];
sprintf(buf_size_str, "%d", buf_size); // buf_size must be a char*
execl("./Monitor","Monitor", buf_size_str, m_info[index].read_p, m_info[index].write_p, (char * )NULL);
perror("execl");
exit(1);
}
//else
m_info[index].m_pid = pid; // Store it's pid
}
/* ========================================================================= */
// If <setup> is true, create a directory to store fifos.
void create_unique_fifo(bool setup, Monitors *m_info, int index)
{
static char fifo_name[32];
static int counter = 0;
if (setup == true)
{
char dir_path[] = "named_fifos";
if (access(dir_path, F_OK) == 0) // If dir already exists (due to abnormal previous termination, eg: SIGKILL)
delete_flat_dir(dir_path); // completely remove it
if (mkdir(dir_path, 0777) == -1){perror("mkdir @ unique_fifo");exit(1);}
sprintf(fifo_name, "named_fifos/f");
return;
}
struct stat stat_temp;
// Create a unique name (e.g named_fifos1R , named_fifos6W )
sprintf(m_info[index].read_p, "%s%d%c", fifo_name, counter, 'R');
// Create fifos
if(stat(m_info[index].read_p, &stat_temp) == -1){
if (mkfifo(m_info[index].read_p,0666) < 0 ){perror("mkfifo @ unique_fifo");exit(1);}
}
m_info[index].read_fd = open(m_info[index].read_p, O_RDONLY | O_NONBLOCK);
if (m_info[index].read_fd == -1) {perror("open @ 73 setup_monitors");exit(1);}
sprintf(m_info[index].write_p, "%s%d%c", fifo_name, counter, 'W');
++counter; // counter used for pipe names
}
/* ========================================================================= */
// Remove a flat directory and its contents.
void delete_flat_dir(char *init_flat_path)
{
char flat_path[32];
strcpy(flat_path, init_flat_path);
DIR *dir = opendir(flat_path);
if (dir == NULL){perror("opendir @ delete_flat_dir"); exit(1);}
struct dirent *entry;
while ((entry = readdir(dir)) != NULL) // Delete contents/files
{
char *f_name = entry->d_name;
if (!strcmp(f_name, ".") || !strcmp(f_name, ".."))
continue;
char f_path[32];
snprintf(f_path, 32, "%s/%s", flat_path, f_name); // Remove file
if (remove(f_path) == -1){perror("remove @ delete_flat_dir"); exit(1);}
}
// Remove dir
if (closedir(dir) == -1){perror("closedir 2 @ delete_flat_dir"); exit(1);}
if (rmdir(flat_path) == -1){perror("rmdir @ delete_flat_dir"); exit(1);}
}
Here are the functions used for the communication of the processes and parent:
// Sends <message> to file descriptor <fd>
void send_message(int fd, char *message, int buf_size)
{
int length = strlen(message);
char buffer[10];
sprintf(buffer, "%d@", length);
write(fd, buffer, 9); // sending the number of bytes reader is about to read
write(fd, message, length); // sending the message itself
}
char *read_message(int read_end_fd, int buf_size)
{
char buffer[10];
int fifo_buffer_size = buf_size;
read(read_end_fd, buffer, 9);
char * tok = strtok(buffer, "@");
int length = atoi(tok); // how many characters will be received
char * input_read = new char[length + 1];
char * str = input_read;
int bytes_read = 0, total_bytes = 0; // We might need to read less or more bytes
fifo_buffer_size = length < fifo_buffer_size ? length : fifo_buffer_size; // // than <buf_size>
while(total_bytes < length)
{
str += bytes_read; // move str pointer
bytes_read = read(read_end_fd, str, fifo_buffer_size); //and read the next <buf_size> characters
total_bytes += bytes_read; // adding them to the total amount of bytes read altogether
if((total_bytes + fifo_buffer_size) > length)
fifo_buffer_size = length - total_bytes; // reading exactly the amount that's left
}
input_read[length] = '\0';
return input_read;
}
我正在使用 valgrind 调试器并在 num_monitors=5 和 buf_size=2 时得到以下结果：
int create_unique_fifo(char* read_fifo)
{
int read_fd;
struct stat stat_temp;
// Create fifos
if(stat(read_fifo, &stat_temp) == -1){
if (mkfifo(read_fifo,0666) < 0 ){perror("mkfifo @ unique_fifo 37");exit(1);}
}
read_fd = open(read_fifo, O_RDONLY); // Open named pipe for reading
if (read_fd == -1){perror("open @ monitor.cpp 1"); exit(1);}
return read_fd;
}
int main(int argc, char* argv[])
{
int buf_size = stoi(argv[1]); // Process command line args
char read_fifo[100], write_fifo[100];
strcpy(write_fifo, argv[2]); // parent read - monitor write
strcpy(read_fifo, argv[3]); // parent write - monitor read
int read_fd, write_fd;
read_fd = create_unique_fifo(read_fifo);
write_fd = open(write_fifo, O_WRONLY | O_NONBLOCK); // Open named pipe for writing
if (write_fd == -1){perror("open @ monitor.cpp 2"); exit(1);}
char* message;
message = read_message(read_fd, buf_size);
cout << "2:" << message << endl;
return 0;
}
知道为什么会发生这种情况吗？我在创建进程后添加了 sleep(1) 以确保及时创建所有先进先出，但仍然出现此错误...任何帮助将不胜感激
答案 0 :(得分：2)
在 send_message 中，您总是从 buffer 写入 9 个字节，但并非所有这些字节都已写入值。这是因为填充 sprintf 的 buffer 只写入前几个位置，可能少至 3 个。
解决方案是要么将它们全部初始化为 0
char buffer[10] = 0;
或者只写字符串中的字节数。从 sprintf 返回的值很容易知道这一点。
auto buf_len = sprintf(buffer, "%d@", length);
write(fd, buffer, buf_len);