我是C的新手，而我只想尝试运行Pacheco的这本代码＆＃34; 并行编程简介＆＃ 34 ;.而且我无法弄清楚如何在main()中实现信号量初始化。是&semaphores[dest]和&semaphores[my_rank]数组吗？
C代码：
/* messages is allocated and initialized to NULL in main */
/* semaphores is allocated and initialized to 0 (locked) in main */
void *Send_msg(void* rank) {
long my_rank = (long) rank;
long dest = (my_rank + 1) % thread_count;
char* my_msg = (char*)malloc(MSG_MAX*sizeof(char));
sprintf(my_msg, "Hello to %ld from %ld", dest, my_rank);
messages[dest] = my_msg;
sem_post(&semaphores[dest])
/* ‘‘Unlock’’ the semaphore of dest */
sem_wait(&semaphores[my_rank]);/* Wait for our semaphore to be unlocked */
printf("Thread %ld > %s\n", my_rank, messages[my_rank]);
return NULL;
} /* Send_msg */
我想实现这种类型的订单机制，因为我正在尝试将输出数组写入文件。这是我的代码：
int k = 0;
long dest = (my_rank + 1) % THREAD_COUNT;
if(genCount%50==0){
//incrementing file name
//semapthore lock
sem_post(&semaphores[dest]);
sem_wait(&semaphores[my_rank]);
snprintf(buffer, sizeof(char) * 32, "file%i.dat", k);
//open the file
fp = fopen(buffer, "r+");
if (fp == NULL) {
printf("I couldn't open file for writing.\n");
exit(0);
}
int loop1, loop2;
//outputting the array into the file
for (loop1 = my_first_i; loop1 < my_last_i; loop1++){
for(loop2 = my_first_i; loop2 < my_last_i; loop2++){
fprintf(fp,"%d\t", map[loop1][loop2]);
}
}
//close the file
fclose(fp);
k++;
}
main()中的信号量初始化：
int semCount;
for(semCount = 0; semCount < THREAD_COUNT; semCount++){
sem_init(&semaphores[semCount], 0, 1);
}
我也将它作为全局变量：
#define THREAD_COUNT 4
sem_t semaphores[THREAD_COUNT];
程序编译，但它给了我这个错误：
*** Error in `./ebola_serial': double free or corruption (out): 0x00007f49700008c0 ***
*** Error in `======= Backtrace: =========
/lib64/libc.so.6(+0x7238e)[0x7f49868f038e]
./ebola_serial/lib64/libc.so.6(+0x7a0c8)[0x7f49868f80c8]
': /lib64/libc.so.6(cfree+0x48)[0x7f49868fb798]
double free or corruption (out)/lib64/libc.so.6(fclose+0x113)[0x7f49868e6473]
./ebola_serial[0x401717]
/lib64/libpthread.so.0(+0x75bd)[0x7f4986c395bd]
: 0x/lib64/libc.so.6(clone+0x6d)[0x7f498697562d]
======= Memory map: ========
00007f49700008c000400000-00402000 r-xp 00000000 08:01 802698 /home/name/Desktop/try ca/ebola_serial
00601000-00602000 r--p 00001000 08:01 802698 /home/name/Desktop/try ca/ebola_serial
00602000-00603000 rw-p 00002000 08:01 802698 /home/name/Desktop/try ca/ebola_serial
00603000-009d3000 rw-p 00000000 00:00 0
01b96000-01bb7000 rw-p 00000000 00:00 0 [heap]
7f4970000000-7f4970021000 rw-p 00000000 00:00 0
7f4970021000-7f4974000000 ---p 00000000 00:00 0
7f4978000000-7f4978021000 rw-p 00000000 00:00 0
7f4978021000-7f497c000000 ---p 00000000 00:00 0
7f497c000000-7f497c021000 rw-p 00000000 00:00 0
7f497c021000-7f4980000000 ---p 00000000 00:00 0
7f4980000000-7f4980021000 rw-p 00000000 00:00 0
7f4980021000-7f4984000000 ---p 00000000 00:00 0
7f4984663000-7f4984679000 r-xp 00000000 08:01 131531 /usr/lib64/libgcc_s-4.9.2.so.1
7f4984679000-7f4984878000 ---p 00016000 08:01 131531 /usr/lib64/libgcc_s-4.9.2.so.1
7f4984878000-7f4984879000 r--p 00015000 08:01 131531 /usr/lib64/libgcc_s-4.9.2.so.1
7f4984879000-7f498487a000 rw-p 00016000 08:01 131531 /usr/lib64/libgcc_s-4.9.2.so.1
7f498487a000-7f498487b000 ---p 00000000 00:00 0
7f498487b000-7f498507b000 rw-p 00000000 00:00 0 [stack:7376]
7f498507b000-7f498507c000 ---p 00000000 00:00 0
7f498507c000-7f498587c000 rw-p 00000000 00:00 0
7f498587c000-7f498587d000 ---p 00000000 00:00 0
7f498587d000-7f498607d000 rw-p 00000000 00:00 0 [stack:7374]
7f498607d000-7f498607e000 ---p 00000000 00:00 0
7f498607e000-7f498687e000 rw-p 00000000 00:00 0 [stack:7373]
7f498687e000-7f4986a28000 r-xp 00000000 08:01 130947 /usr/lib64/libc-2.20.so
7f4986a28000-7f4986c28000 ---p 001aa000 08:01 130947 /usr/lib64/libc-2.20.so
7f4986c28000-7f4986c2c000 r--p 001aa000 08:01 130947 /usr/lib64/libc-2.20.so
7f4986c2c000-7f4986c2e000 rw-p 001ae000 08:01 130947 /usr/lib64/libc-2.20.so
7f4986c2e000-7f4986c32000 rw-p 00000000 00:00 0
7f4986c32000-7f4986c49000 r-xp 00000000 08:01 130973 /usr/lib64/libpthread-2.20.so
7f4986c49000-7f4986e48000 ---p 00017000 08:01 130973 /usr/lib64/libpthread-2.20.so
7f4986e48000-7f4986e49000 r--p 00016000 08:01 130973 /usr/lib64/libpthread-2.20.so
7f4986e49000-7f4986e4a000 rw-p 00017000 08:01 130973 /usr/lib64/libpthread-2.20.so
7f4986e4a000-7f4986e4e000 rw-p 00000000 00:00 0
7f4986e4e000-7f4986f53000 r-xp 00000000 08:01 130955 /usr/lib64/libm-2.20.so
7f4986f53000-7f4987152000 ---p 00105000 08:01 130955 /usr/lib64/libm-2.20.so
7f4987152000-7f4987153000 r--p 00104000 08:01 130955 /usr/lib64/libm-2.20.so
7f4987153000-7f4987154000 rw-p 00105000 08:01 130955 /usr/lib64/libm-2.20.so
7f4987154000-7f4987174000 r-xp 00000000 08:01 130940 /usr/lib64/ld-2.20.so
7f4987353000-7f4987356000 rw-p 00000000 00:00 0
7f498736d000-7f4987373000 rw-p 00000000 00:00 0
7f4987373000-7f4987374000 r--p 0001f000 08:01 130940 /usr/lib64/ld-2.20.so
7f4987374000-7f4987376000 rw-p 00020000 08:01 130940 /usr/lib64/ld-2.20.so
7ffce31e3000-7ffce3205000 rw-p 00000000 00:00 0 [stack]
7ffce320d000-7ffce320f000 r--p 00000000 00:00 0 [vvar]
7ffce320f000-7ffce3211000 r-xp 00000000 00:00 0 [vdso]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
Aborted
任何帮助都将不胜感激。
答案 0 :(得分：1)
看起来像这样定义的信号量
sem_t semaphores[N];
其中N是信号量的数量
对于初始化信号量，你应该使用sem_init函数，它接受一个指向所需信号量的指针，这是一个标志，它允许共享进程使用和信号量的初始值。
sem_init(&semaphores[0], 0, 1);
在您的情况下，信号量实例存储在名为semaphores的数组中，因此您必须迭代数组的所有成员以进行初始化
int i;
for(i=0;i<N;i++)
sem_init(&semaphores[i], 0, 1);
使用信号量的Finlay你必须以这种方式调用sem_wait和sem_post函数
sem_wait(&semaphores[0 to N-1]); // Locking semaphore
sem_post(&semaphores[0 to N-1]); // Unlocking it