name semaphore는 /dev/shm에 저장된다. 이름을 엄한 /tmp/xxx 이런 식으로 만들면 세마포어를 만들 수 없다. segment error로 죽는다. 책에서는 /tmp/로 넣어도 잘 동작해서 확인하는데 오래 걸렸다.
디버그 하다 중간에 멈추면 /dev/shm에 sem*로 파일을 지울 수 없어 다음 실행에 세마포어를 받을 수 없다. 처음 시작 전 자기 이름으로 된 세마포어 있으면 지워야 한다.
thread를 돌리면 미친 race condition이 피곤하게 한다. 참 헷갈리는데, 자주보면 익숙해 지겠지. thread를 돌리면 순서는 이제 별 의미 없는 듯 하다. sem_post하는 즉시 자기 thread를 실행하는게 아니라 다른 thread로 가서 프로그램을 실행한다. wait로 thread 이후 행을 잘 막는 게 핵심인 듯 하다.
/* include main */
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <semaphore.h>
#include <sys/stat.h>
#define NBUFF 10
#define SEM_MUTEX "mutex" /* these are args to px_ipc_name() */
#define SEM_NEMPTY "empty"
#define SEM_NSTORED "nstored"
int nitems; /* read-only by producer and consumer */
struct { /* data shared by producer and consumer */
int buff[NBUFF];
sem_t *mutex, *nempty, *nstored;
} shared;
void *produce(void *), *consume(void *);
int
main(int argc, char **argv)
{
pthread_t tid_produce, tid_consume;
int errno;
if (argc != 2)
perror("usage: prodcons1 <#items>");
nitems = atoi(argv[1]);
/* 4create three semaphores */
shared.mutex = sem_open(SEM_MUTEX, O_CREAT | O_EXCL,
0660, 1);
shared.nempty = sem_open(SEM_NEMPTY, O_CREAT | O_EXCL,
0660, NBUFF);
shared.nstored = sem_open(SEM_NSTORED, O_CREAT | O_EXCL,
0660, 0);
/* 4create one producer thread and one consumer thread */
//pthread_setconcurrency(2);
//pthread_setconcurrency();
pthread_create(&tid_produce, NULL, produce, NULL);
pthread_create(&tid_consume, NULL, consume, NULL);
/* 4wait for the two threads */
pthread_join(tid_produce, NULL);
pthread_join(tid_consume, NULL);
/* 4remove the semaphores */
sem_unlink(SEM_MUTEX);
sem_unlink(SEM_NEMPTY);
sem_unlink(SEM_NSTORED);
exit(0);
}
/* end main */
/* include prodcons */
void *
produce(void *arg)
{
int i;
int tmpnempty, tmpmutex, tmpnstored;
for (i = 0; i < nitems; i++) {
//value check
//sem_getvalue(shared.nempty, &tmpnempty);
//sem_getvalue(shared.nstored, &tmpnstored);
//sem_getvalue(shared.mutex, &tmpmutex);
sem_wait(shared.nempty); /* wait for at least 1 empty slot */
sem_wait(shared.mutex);
//value check
//sem_getvalue(shared.nempty, &tmpnempty);
//sem_getvalue(shared.nstored, &tmpnstored);
//sem_getvalue(shared.mutex, &tmpmutex);
shared.buff[i % NBUFF] = i; /* store i into circular buffer */
sem_post(shared.mutex);
sem_post(shared.nstored); /* 1 more stored item */
//value check
//sem_getvalue(shared.nempty, &tmpnempty);
//sem_getvalue(shared.nstored, &tmpnstored);
//sem_getvalue(shared.mutex, &tmpmutex);
}
return(NULL);
}
void *
consume(void *arg)
{
int i;
int tmpnempty, tmpmutex, tmpnstored;
for (i = 0; i < nitems; i++) {
//value check
//sem_getvalue(shared.nempty, &tmpnempty);
//sem_getvalue(shared.mutex, &tmpmutex);
//sem_getvalue(shared.nstored, &tmpnstored);
sem_wait(shared.nstored); /* wait for at least 1 stored item */
sem_wait(shared.mutex);
//value check
//sem_getvalue(shared.nempty, &tmpnempty);
//sem_getvalue(shared.mutex, &tmpmutex);
//sem_getvalue(shared.nstored, &tmpnstored);
if (shared.buff[i % NBUFF] = i)
printf("buff[%d] = %d\n", i, shared.buff[i % NBUFF]);
sem_post(shared.mutex);
sem_post(shared.nempty); /* 1 more empty slot */
//value check
//sem_getvalue(shared.nempty, &tmpnempty);
//sem_getvalue(shared.mutex, &tmpmutex);
//sem_getvalue(shared.nstored, &tmpnstored);
}
return(NULL);
}
/* end prodcons */
pi@raspberrypi:~/Project/cCode/IPC $ gdb --args ./a.out 3
GNU gdb (Raspbian 8.2.1-2) 8.2.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "arm-linux-gnueabihf".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./a.out...done.
...
(gdb) info b
Num Type Disp Enb Address What
1 breakpoint keep y 0x000107b4 in produce at semaphore.c:72
breakpoint already hit 3 times
2 breakpoint keep y 0x00010884 in consume at semaphore.c:108
breakpoint already hit 3 times
(gdb) r
Starting program: /home/pi/Project/cCode/IPC/a.out 3
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".
[New Thread 0xb6e31460 (LWP 2842)]
[New Thread 0xb6630460 (LWP 2843)]
[Switching to Thread 0xb6e31460 (LWP 2842)]
Thread 2 "a.out" hit Breakpoint 1, produce (arg=0x0) at semaphore.c:72
72 sem_wait(shared.nempty); /* wait for at least 1 empty slot */
1: shared = {buff = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, mutex = 0xb6ff8000,
nempty = 0xb6ff7000, nstored = 0xb6ff6000}
2: *shared.nempty = {
__size = "\024\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 20}
3: *shared.nstored = {
__size = "\000\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 0}
4: *shared.mutex = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
(gdb) c
Continuing.
[Switching to Thread 0xb6630460 (LWP 2843)]
Thread 3 "a.out" hit Breakpoint 2, consume (arg=0x0) at semaphore.c:108
108 sem_wait(shared.nstored); /* wait for at least 1 stored item */
1: shared = {buff = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, mutex = 0xb6ff8000,
nempty = 0xb6ff7000, nstored = 0xb6ff6000}
2: *shared.nempty = {
__size = "\024\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 20}
3: *shared.nstored = {
__size = "\000\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 0}
4: *shared.mutex = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
(gdb) c
Continuing.
[Switching to Thread 0xb6e31460 (LWP 2842)]
Thread 2 "a.out" hit Breakpoint 1, produce (arg=0x0) at semaphore.c:72
72 sem_wait(shared.nempty); /* wait for at least 1 empty slot */
1: shared = {buff = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, mutex = 0xb6ff8000,
nempty = 0xb6ff7000, nstored = 0xb6ff6000}
2: *shared.nempty = {
__size = "\022\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 18}
3: *shared.nstored = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
4: *shared.mutex = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
(gdb) c
Continuing.
[Switching to Thread 0xb6630460 (LWP 2843)]
Thread 3 "a.out" hit Breakpoint 2, consume (arg=0x0) at semaphore.c:108
108 sem_wait(shared.nstored); /* wait for at least 1 stored item */
1: shared = {buff = {0, 1, 0, 0, 0, 0, 0, 0, 0, 0}, mutex = 0xb6ff8000,
nempty = 0xb6ff7000, nstored = 0xb6ff6000}
2: *shared.nempty = {
__size = "\022\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 18}
3: *shared.nstored = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
4: *shared.mutex = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
(gdb) c
Continuing.
[Switching to Thread 0xb6e31460 (LWP 2842)]
Thread 2 "a.out" hit Breakpoint 1, produce (arg=0x0) at semaphore.c:72
72 sem_wait(shared.nempty); /* wait for at least 1 empty slot */
1: shared = {buff = {0, 1, 0, 0, 0, 0, 0, 0, 0, 0}, mutex = 0xb6ff8000,
nempty = 0xb6ff7000, nstored = 0xb6ff6000}
2: *shared.nempty = {
__size = "\022\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 18}
3: *shared.nstored = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
4: *shared.mutex = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
(gdb) c
Continuing.
buff[1] = 1
[Thread 0xb6e31460 (LWP 2842) exited]
[Switching to Thread 0xb6630460 (LWP 2843)]
Thread 3 "a.out" hit Breakpoint 2, consume (arg=0x0) at semaphore.c:108
108 sem_wait(shared.nstored); /* wait for at least 1 stored item */
1: shared = {buff = {0, 1, 2, 0, 0, 0, 0, 0, 0, 0}, mutex = 0xb6ff8000,
nempty = 0xb6ff7000, nstored = 0xb6ff6000}
2: *shared.nempty = {
__size = "\022\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 18}
3: *shared.nstored = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
4: *shared.mutex = {
__size = "\002\000\000\000\200\000\000\000\000\000\000\000\000\000\000",
__align = 2}
(gdb) c
Continuing.
buff[2] = 2
[Thread 0xb6ffa070 (LWP 2841) exited]
[Inferior 1 (process 2841) exited normally]
(gdb)