linux中的程序通訊分為三個部分：低階通訊，管道通訊和程序間通訊IPC（inter process communication）。linux的低階通訊主要用來傳遞程序的控制訊號——檔案鎖和軟中斷訊號機制。linux的程序間通訊IPC有三個部分——①訊號量，②共享記憶體和③訊息佇列。以下是我編寫的linux程序通訊的C語言實現程式碼。作業系統為redhat9.0，編輯器為vi，編譯器採用gcc。下面所有實現程式碼均已經通過測試，執行無誤。

一.低階通訊--訊號通訊

signal.c

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

/*捕捉到訊號sig之後，執行預先預定的動作函式*/
void sig_alarm(int sig)
{
 printf("---the signal received is %d. /n", sig);
 signal(SIGINT, SIG_DFL); //SIGINT終端中斷訊號，SIG_DFL：恢復預設行為，SIN_IGN：忽略訊號
}

int main()
{
 signal(SIGINT, sig_alarm);//捕捉終端中斷訊號

 while(1)
 {
  printf("waiting here!/n");
  sleep(1);
 }
 return 0;
}

二.管道通訊

pipe.c

#include <stdio.h>

#define BUFFER_SIZE 30

int main()
{
 int x;
 int fd[2];
 char buf[BUFFER_SIZE];
 char s[BUFFER_SIZE];
 pipe(fd);//建立管道

 while((x=fork())==-1);//建立管道失敗時，進入迴圈
 
 /*進入子程序，子程序向管道中寫入一個字串*/
 if(x==0)
 {
  sprintf(buf,"This is an example of pipe!/n");
  write(fd[1],buf,BUFFER_SIZE);
  exit(0);
 }

 /*進入父程序，父程序從管道的另一端讀出剛才寫入的字串*/
 else
 {
  wait(0);//等待子程序結束
  read(fd[0],s,BUFFER_SIZE);//讀出字串，並將其儲存在char s[]中
  printf("%s",s);//列印字串
 }
 return 0;
}

三.程序間通訊——IPC

①訊號量通訊

sem.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>

/*聯合體變數*/
union semun
{
 int val; //訊號量初始值                  
 struct semid_ds *buf;       
 unsigned short int *array; 
 struct seminfo *__buf;     
};

/*函式宣告，訊號量定義*/
static int set_semvalue(void); //設定訊號量
static void del_semvalue(void);//刪除訊號量
static int semaphore_p(void);  //執行P操作
static int semaphore_v(void);  //執行V操作
static int sem_id;             //訊號量識別符號

int main(int argc, char *argv[])
{
 int i;
 int pause_time;
 char op_char = 'O';
 srand((unsigned int)getpid()); 
 sem_id = semget((key_t)1234, 1, 0666 | IPC_CREAT);//建立一個訊號量,IPC_CREAT表示建立一個新的訊號量
 
 /*如果有引數，設定訊號量，修改字元*/
 if (argc > 1)
 {
  if (!set_semvalue())
  {
   fprintf(stderr, "Failed to initialize semaphore/n");
   exit(EXIT_FAILURE);
  }
  op_char = 'X';
  sleep(5);
 }

 for(i = 0; i < 10; i++)  
 {      

  /*執行P操作*/
  if (!semaphore_p())
   exit(EXIT_FAILURE);

  printf("%c", op_char);
  fflush(stdout);
  pause_time = rand() % 3;
  sleep(pause_time);
  printf("%c", op_char);
  fflush(stdout);

  /*執行V操作*/
  if (!semaphore_v())
   exit(EXIT_FAILURE);

  pause_time = rand() % 2;
  sleep(pause_time);
 }  
 printf("/n%d - finished/n", getpid());

 if (argc > 1)
 {   
  sleep(10);
  del_semvalue(); //刪除訊號量
 }   
 exit(EXIT_SUCCESS);
}

/*設定訊號量*/
static int set_semvalue(void)
{
 union semun sem_union;
 sem_union.val = 1;
 if (semctl(sem_id, 0, SETVAL, sem_union) == -1)
  return(0);
 
 return(1);
}

/*刪除訊號量*/
static void del_semvalue(void)
{
 union semun sem_union; 
 if (semctl(sem_id, 0, IPC_RMID, sem_union) == -1)
  fprintf(stderr, "Failed to delete semaphore/n");
}

/*執行P操作*/
static int semaphore_p(void)
{
 struct sembuf sem_b;  
 sem_b.sem_num = 0;
 sem_b.sem_op = -1; /* P() */
 sem_b.sem_flg = SEM_UNDO;
 if (semop(sem_id, &sem_b, 1) == -1)
 {
  fprintf(stderr, "semaphore_p failed/n");
  return(0);
 }
 return(1);
}

/*執行V操作*/
static int semaphore_v(void)
{
 struct sembuf sem_b;
 sem_b.sem_num = 0;
 sem_b.sem_op = 1; /* V() */
 sem_b.sem_flg = SEM_UNDO;
 if (semop(sem_id, &sem_b, 1) == -1)
 {
  fprintf(stderr, "semaphore_v failed/n");
  return(0);
 }
 return(1);
}

②訊息佇列通訊

send.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>
#define MAX_TEXT 512

/*用於訊息收發的結構體--my_msg_type：訊息型別，some_text：訊息正文*/
struct my_msg_st
{
 long int my_msg_type;
 char some_text[MAX_TEXT];
};

int main()
{
 int running = 1;//程式執行識別符號
 struct my_msg_st some_data;
 int msgid;//訊息佇列識別符號
 char buffer[BUFSIZ];

 /*建立與接受者相同的訊息佇列*/
 msgid = msgget((key_t)1234, 0666 | IPC_CREAT);
 if (msgid == -1)
 {
  fprintf(stderr, "msgget failed with error: %d/n", errno);
  exit(EXIT_FAILURE);
    }

 /*向訊息佇列中傳送訊息*/
 while(running)
 {
  printf("Enter some text: ");
  fgets(buffer, BUFSIZ, stdin);
  some_data.my_msg_type = 1;
  strcpy(some_data.some_text, buffer);
  if (msgsnd(msgid, (void *)&some_data, MAX_TEXT, 0) == -1)
  {
   fprintf(stderr, "msgsnd failed/n");
   exit(EXIT_FAILURE);
  }
  if (strncmp(buffer, "end", 3) == 0)
  {
   running = 0;
  }
 }
 exit(EXIT_SUCCESS);
}

receive.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

/*用於訊息收發的結構體--my_msg_type：訊息型別，some_text：訊息正文*/
struct my_msg_st
{
 long int my_msg_type;
 char some_text[BUFSIZ];
};

int main()
{
 int running = 1;//程式執行識別符號
 int msgid; //訊息佇列識別符號
 struct my_msg_st some_data;
 long int msg_to_receive = 0;//接收訊息的型別--0表示msgid佇列上的第一個訊息

 /*建立訊息佇列*/
 msgid = msgget((key_t)1234, 0666 | IPC_CREAT);
 if (msgid == -1)
 {
  fprintf(stderr, "msgget failed with error: %d/n", errno);
  exit(EXIT_FAILURE);
 }

 /*接收訊息*/
 while(running)
 {
  if (msgrcv(msgid, (void *)&some_data, BUFSIZ,msg_to_receive, 0) == -1)
  {
   fprintf(stderr, "msgrcv failed with error: %d/n", errno);
   exit(EXIT_FAILURE);
  }
  printf("You wrote: %s", some_data.some_text);
  if (strncmp(some_data.some_text, "end", 3) == 0)
  {
   running = 0;
  }
 }

 /*刪除訊息佇列*/
 if (msgctl(msgid, IPC_RMID, 0) == -1)
 {
  fprintf(stderr, "msgctl(IPC_RMID) failed/n");
  exit(EXIT_FAILURE);
 }
 exit(EXIT_SUCCESS);
}

③共享記憶體通訊

share.h

#define TEXT_SZ 2048 //申請共享記憶體大小

struct shared_use_st
{
 int written_by_you; //written_by_you為1時表示有資料寫入，為0時表示資料已經被消費者提走
 char some_text[TEXT_SZ];
};

producer.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include "share.h"

int main()
{
 int running = 1; //程式執行標誌位
 void *shared_memory = (void *)0;
 struct shared_use_st *shared_stuff;
 char buffer[BUFSIZ];
 int shmid; //共享記憶體識別符號

 /*建立共享記憶體*/
 shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT);
 if (shmid == -1)
 {
  fprintf(stderr, "shmget failed/n");
  exit(EXIT_FAILURE);
 }

 /*將共享記憶體連線到一個程序的地址空間中*/
 shared_memory = shmat(shmid, (void *)0, 0);//指向共享記憶體第一個位元組的指標
 if (shared_memory == (void *)-1)
 {
  fprintf(stderr, "shmat failed/n");
  exit(EXIT_FAILURE);
 }

 printf("Memory attached at %X/n", (int)shared_memory);
 shared_stuff = (struct shared_use_st *)shared_memory;

 /*生產者寫入資料*/
 while(running)
 {
  while(shared_stuff->written_by_you == 1)
  {
   sleep(1);           
   printf("waiting for client.../n");
  }
  printf("Enter some text: ");
  fgets(buffer, BUFSIZ, stdin);
  strncpy(shared_stuff->some_text, buffer, TEXT_SZ);
  shared_stuff->written_by_you = 1;
  if (strncmp(buffer, "end", 3) == 0)
  {
   running = 0;
  }
 }

    /*該函式用來將共享記憶體從當前程序中分離,僅使得當前程序不再能使用該共享記憶體*/
 if (shmdt(shared_memory) == -1)
 {
  fprintf(stderr, "shmdt failed/n");
  exit(EXIT_FAILURE);
 }

 printf("producer exit./n");
 exit(EXIT_SUCCESS);
}

customer.c

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include "share.h"

int main()
{
 int running = 1;//程式執行標誌位
 void *shared_memory = (void *)0;
 struct shared_use_st *shared_stuff;
 int shmid; //共享記憶體識別符號
 srand((unsigned int)getpid());   

 /*建立共享記憶體*/
 shmid = shmget((key_t)1234, sizeof(struct shared_use_st), 0666 | IPC_CREAT);
 if (shmid == -1)
 {
  fprintf(stderr, "shmget failed/n");
  exit(EXIT_FAILURE);
 }

 /*將共享記憶體連線到一個程序的地址空間中*/
 shared_memory = shmat(shmid, (void *)0, 0);//指向共享記憶體第一個位元組的指標
 if (shared_memory == (void *)-1)
 {
  fprintf(stderr, "shmat failed/n");
  exit(EXIT_FAILURE);
 }

 printf("Memory attached at %X/n", (int)shared_memory);
 shared_stuff = (struct shared_use_st *)shared_memory;
 shared_stuff->written_by_you = 0;

 /*消費者讀取資料*/
 while(running)
 {
  if (shared_stuff->written_by_you)
  {
   printf("You wrote: %s", shared_stuff->some_text);
   sleep( rand() % 4 ); 
   shared_stuff->written_by_you = 0;
   if (strncmp(shared_stuff->some_text, "end", 3) == 0)
   {
    running = 0;
   }
  }
 }

 /*該函式用來將共享記憶體從當前程序中分離,僅使得當前程序不再能使用該共享記憶體*/
 if (shmdt(shared_memory) == -1)
 {
  fprintf(stderr, "shmdt failed/n");
  exit(EXIT_FAILURE);
 }

 /*將共享記憶體刪除,所有程序均不能再訪問該共享記憶體*/
 if (shmctl(shmid, IPC_RMID, 0) == -1)
 {
  fprintf(stderr, "shmctl(IPC_RMID) failed/n");
  exit(EXIT_FAILURE);
 }

 exit(EXIT_SUCCESS);
}