Linux多線程同步之消息隊(duì)列
消息隊(duì)列是消息的鏈表，存放在內(nèi)核中并有消息隊(duì)列標(biāo)示符標(biāo)示。
msgget用于創(chuàng)建一個(gè)新隊(duì)列或打開一個(gè)現(xiàn)存的隊(duì)列。msgsnd將新消息加入到消息隊(duì)列中；每個(gè)消息包括一個(gè)long型的type；和消息緩存；msgrcv用于從隊(duì)列中取出消息；取消息很智能，不一定先進(jìn)先出
①msgget，創(chuàng)建一個(gè)新隊(duì)列或打開一個(gè)現(xiàn)有隊(duì)列
#include
int msgget ( key_t key, int flag )；
//成功返回消息隊(duì)列ID；錯(cuò)誤返回-1
②msgsnd: 發(fā)送消息
#include
int msgsnd( int msgid, const void* ptr, size_t nbytes, int flag )
//成功返回0，錯(cuò)誤返回-1
a: flag可以指定為IPC_NOWAIT; 若消息隊(duì)列已滿，則msgsnd立即出錯(cuò)返回EABAIN；
若沒指定IPC_NOWAIT； msgsnd會(huì)阻塞，直到消息隊(duì)列有空間為止
③msgrcv: 讀取消息：
ssize_t msgrcv( int msgid, void* ptr, size_t nbytes, long type, int flag );
a. type == 0; 返回消息隊(duì)列中***個(gè)消息，先進(jìn)先出
b. type > 0 返回消息隊(duì)列中類型為tpye的***個(gè)消息
c. type < 0 返回消息隊(duì)列中類型 <= |type| 的數(shù)據(jù)；若這種消息有若干個(gè)，則取類型值最小的消息
消息隊(duì)列創(chuàng)建步驟：
#define MSG_FILE "."
struct msgtype {
long mtype;
char buffer[BUFFER+1];
};
if((key=ftok(MSG_FILE,'a'))==-1)
{
fprintf(stderr,"Creat Key Error:%s\n", strerror(errno));
exit(1);
}
if((msgid=msgget(key, IPC_CREAT | 0666/*PERM*/))==-1)
{
fprintf(stderr,"Creat Message Error:%s\n", strerror(errno));
exit(1);
}
msg.mtype = 1;
strncpy(msg.buffer, argv[1], BUFFER);
msgsnd(msgid, &msg, sizeof(struct msgtype), 0);
msgrcv(msgid, &msg, sizeof(struct msgtype), 1, 0);
示例代碼：
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define MSG_FILE "."
#define BUFFER 255
#define PERM S_IRUSR|S_IWUSR
#define IPCKEY 0x111
struct msgtype {
long mtype;
char buffer[BUFFER+1];
};
void* thr_test( void* arg ){
struct msgtype msg;
int msgid;
msgid = *((int*)arg);
printf("msqid = %d IPC_NOWAIT = %d\n", msgid, IPC_NOWAIT);
time_t tt = time(0)+8;
//while( time(0) <= tt )
//{
msgrcv(msgid, &msg, sizeof(struct msgtype), 1, 0);
fprintf(stderr,"Server Receive:%s\n", msg.buffer);
msg.mtype = 2;
msgsnd(msgid, &msg, sizeof(struct msgtype), 0);
//}
pthread_exit( (void*)2 );
}
int main(int argc, char **argv)
{
struct msgtype msg;
key_t key;
int msgid;
pthread_t tid;
if(argc != 2)
{
fprintf(stderr,"Usage:%s string\n", argv[0]);
exit(1);
}
/*
char path[256];
sprintf( path, "%s/", (char*)getenv("HOME") );
printf( "path is %s\n", path );
msgid=ftok( path, IPCKEY );
*/
if((key=ftok(MSG_FILE,'a'))==-1)
{
fprintf(stderr,"Creat Key Error:%s\n", strerror(errno));
exit(1);
}
if((msgid=msgget(key, IPC_CREAT | 0666/*PERM*/))==-1)
{
fprintf(stderr,"Creat Message Error:%s\n", strerror(errno));
exit(1);
}
pthread_create( &tid, NULL, thr_test, &msgid );
fprintf(stderr,"msid is :%d\n", msgid);
msg.mtype = 1;
strncpy(msg.buffer, argv[1], BUFFER);
msgsnd(msgid, &msg, sizeof(struct msgtype), 0);
exit(0);
}
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