The method of inter-process communication under Linux--signal volume

The signal volume here is mainly used between different processes.
Requires four operations

1. P operation
2. V Operation
3. The semaphore is initialized with the SEMCTL call command parameter setting Setval, which must be done before the semaphore is used.
4. And you can delete the semaphore ID by semctl Call command set to Ipc_rmid:

Because the union Semun is not defined in the library, it needs to be defined by itself.

Three functions to use the semaphore

1. Semget used to create a new semaphore or to obtain a key with an existing semaphore
2. Semop used to change the semaphore value
3. Semctl is used to directly control semaphore information, such as SEMOP must first use SEMCTL to give an initial value

#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <sys/sem.h>Unionsemun{intValstructSemid_ds *buf;unsigned  Short int*Array;structSeminfo *__buf;};Static intSet_semvalue (void);Static voidDel_semvalue (void);Static intSemaphore_p (void);Static intSemaphore_v (void);Static intsem_id;Static intSet_semvalue (void){UnionSemun sem_union; Sem_union.val=1; Semctl (sem_id,0, setval,sem_union);}Static voidDel_semvalue (void){UnionSemun sem_union; Semctl (sem_id,0, ipc_rmid,sem_union);}Static intSemaphore_p (void){structSembuf Sem_b; sem_b.sem_num=0; sem_b.sem_op=-1; Sem_b.sem_flg=sem_undo;//auto ReleaseSemop (Sem_id,&sem_b,1);}Static intSemaphore_v (void){structSembuf Sem_b; sem_b.sem_num=0; sem_b.sem_op=1; Sem_b.sem_flg=sem_undo;//auto ReleaseSemop (Sem_id,&sem_b,1);}//main FunctionintMainintargcChar*agrv[]) {intIintPause_time;CharOp_char=' O '; Srand ((unsigned int) getpid ()); Sem_id=semget ((key_t)1234,1,0666| Ipc_creat);if(argc>1) {Set_semvalue (); Op_char=' X '; Sleep2); } for(i=0;i<Ten; i++) {semaphore_p ();printf("%c", Op_char);        Fflush (stdout); Pause_time=rand ()%3; Sleep (Pause_time);printf("%c", Op_char);        Fflush (stdout);        Semaphore_v (); Pause_time=rand ()%2;    Sleep (Pause_time); }printf("\n%d-finished\n", Getpid ());if(argc>1) {Sleep (Ten);    Del_semvalue (); }Exit(0);}

[Email protected]:~/mytest./sem1 1 &
[1] 12839
[Email protected]:~/mytest ./sem1
Ooxxooxxooxxooxxooxxxxooxxooxxooxxooxxoo

12839-finished
12840-finished
[Email protected]:~/mytest$

The method of inter-process communication under Linux--signal volume