我正在使用POSIX库练习信号量。我试图通过一个信号量（代表一个服务器）传递线程（代表客户），这个信号量在两个表（每个由sempahores控制）下有8个人。我认为罪魁祸首是解锁和锁定多个信号量的顺序，但我似乎无法定位非法指令（核心转储）错误的来源。
EDITED - 互斥初始化的反转顺序和创建线程循环 - 添加返回NULL到eat（）的结尾：
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
sem_t server_sem;
int server_pshared;
int server_ret;
int server_count = 10;
sem_t tablea_sem;
int tablea_pshared;
int tablea_ret;
int tablea_count = 4;
sem_t tableb_sem;
int tableb_pshared;
int tableb_ret;
int tableb_count = 4;
//server_ret = serm_open("serverSem", O_CREAT | O_EXCL, 0644, server_count);
int customer_count = 10;
pthread_t customer[10];
//pthread_t plates[8]
int plate_count = 8;
pthread_mutex_t plates[8];
void *eat(int n) {
sem_wait(&server_sem);
printf("Sitting down at Table A\n");
//unlock table a semaphore
sem_wait(&tablea_sem);
//unlock
pthread_mutex_lock(&plates[n]);
printf("Customer %d is eating\n", n);
sleep(5);
pthread_mutex_unlock(&plates[n]);
printf("Customer %d is finished eating\n", n);
//sem_post(&server_sem);
sem_post(&tablea_sem);
printf("Sitting down at Table A\n");
//unlock table b semaphore
sem_wait(&tableb_sem);
//unlock
//sem_wait(&server_sem);
pthread_mutex_lock(&plates[n]);
printf("Customer %d is eating\n", n);
sleep(5);
pthread_mutex_unlock(&plates[n]);
printf("Customer %d is finished eating\n", n);
sem_post(&tableb_sem);
sem_post(&server_sem);
return NULL;
}
int main() {
server_ret = sem_init(&server_sem, 1, server_count);
tablea_ret = sem_init(&tablea_sem, 1, tablea_count);
tableb_ret = sem_init(&tableb_sem, 1, tableb_count);
//customer = (pthread_t[10] *)malloc(sizeof(customer));
printf ("starting thread, semaphore is unlocked.\n");
int i;
for(i=0;i<plate_count;i++)
pthread_mutex_init(&plates[i],NULL);
for (i=0;i<customer_count;i++)
pthread_create(&customer[i],NULL,(void *)eat,(void *)i);
//for(i=0;i<plate_count;i++)
// pthread_mutex_init(&plates[i],NULL);
for(i=0;i<customer_count;i++)
pthread_join(customer[i],NULL);
for(i=0;i<plate_count;i++)
pthread_mutex_destroy(&plates[i]);
return 0;
}
更新：
我已经接受了答案，因为它让我对我认为最初的问题有了很好的了解。可能仍然存在，而且仅仅是我对这个主题缺乏理解（低估）。一些研究（手册页，以及此thread）让我解决了SO回答者提到的错误，并继续尽力调整这个错误。
现在，下面更新的代码试图解决接受的答案。但是，我得到了相同的输出......我还是忽略了这一点吗？
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdint.h>
sem_t server_sem;
int server_pshared;
int server_ret;
int server_count = 10;
sem_t tablea_sem;
int tablea_pshared;
int tablea_ret;
int tablea_count = 4;
sem_t tableb_sem;
int tableb_pshared;
int tableb_ret;
int tableb_count = 4;
//server_ret = serm_open("serverSem", O_CREAT | O_EXCL, 0644, server_count);
int customer_count = 10;
pthread_t customer[10];
//pthread_t plates[8]
int plate_count = 8;
pthread_mutex_t plates[8];
//void *eat(int n) {
void *eat(void *i) {
//int n = *((int *) i);
int n = (int)(intptr_t) i;
//printf("Customer %d is eating", m);
sem_wait(&server_sem);
int j;
for (j = 0; j<4; j++) {
sem_wait(&tablea_sem);
pthread_mutex_lock(&plates[j]);
printf("Customer %d is eating\n", n);
printf("Plate %d is eaten\n", j);
sleep(5);
pthread_mutex_unlock(&plates[j]);
printf("Customer %d is finished eating\n", n);
sem_post(&tablea_sem);
}
for (j = 4; j<8; j++) {
sem_wait(&tableb_sem);
pthread_mutex_lock(&plates[j]);
printf("Customer %d is eating\n", n);
printf("Plate %d is eaten\n", j);
sleep(5);
pthread_mutex_unlock(&plates[j]);
printf("Customer %d is finished eating\n", n);
sem_post(&tableb_sem);
}
j--;
sem_post(&server_sem);
return (NULL);
}
int main() {
server_ret = sem_init(&server_sem, 1, server_count);
tablea_ret = sem_init(&tablea_sem, 1, tablea_count);
tableb_ret = sem_init(&tableb_sem, 1, tableb_count);
//customer = (pthread_t[10] *)malloc(sizeof(customer));
printf ("starting thread, semaphore is unlocked.\n");
int i;
int j;
int k;
for(i=0;i<plate_count;i++) {
pthread_mutex_init(&plates[i],NULL);
printf("Creating mutex for plate %d\n", i);
}
sem_wait(&server_sem);
for (j=0;j<customer_count;j++) {
pthread_create(&customer[j],NULL,(void *)eat,(void *) (intptr_t) j);
}
for(k=0;k<customer_count;k++) {
pthread_join(customer[k],NULL);
printf("Joining thread %d\n", k);
}
for(i=0;i<plate_count;i++) {
pthread_mutex_destroy(&plates[i]);
}
sem_post(&server_sem);
return 0;
}
使用gdb调试输出（无断点）：
niu@niu-vb:~/Documents/CSU_OS$ gcc -pthread -o -g diner diner4.c
diner: In function `_fini':
(.fini+0x0): multiple definition of `_fini'
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_info): relocation 0 has invalid symbol index 7
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_info): relocation 1 has invalid symbol index 8
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_info): relocation 2 has invalid symbol index 9
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_ranges): relocation 0 has invalid symbol index 4
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_ranges): relocation 1 has invalid symbol index 4
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_ranges): relocation 2 has invalid symbol index 5
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_ranges): relocation 3 has invalid symbol index 5
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crti.o:(.fini+0x0): first defined here
diner: In function `data_start':
(.data+0x0): multiple definition of `__data_start'
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 0 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 1 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 2 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 3 has invalid symbol index 2
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 4 has invalid symbol index 11
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 5 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 6 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 7 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 8 has invalid symbol index 12
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 9 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 10 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 11 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 12 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 13 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 14 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 15 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 16 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 17 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 18 has invalid symbol index 13
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_info): relocation 19 has invalid symbol index 21
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crt1.o(.debug_line): relocation 0 has invalid symbol index 2
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o:(.data+0x0): first defined here
diner: In function `data_start':
(.data+0x8): multiple definition of `__dso_handle'
/usr/lib/gcc/x86_64-linux-gnu/4.8/crtbegin.o:(.data+0x0): first defined here
diner:(.rodata+0x0): multiple definition of `_IO_stdin_used'
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o:(.rodata.cst4+0x0): first defined here
diner: In function `_start':
(.text+0x0): multiple definition of `_start'
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o:/build/eglibc-oGUzwX/eglibc-2.19/csu/../sysdeps/x86_64/start.S:118: first defined here
diner: In function `_init':
(.init+0x0): multiple definition of `_init'
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_line): relocation 0 has invalid symbol index 4
/usr/bin/ld: /usr/lib/debug/usr/lib/x86_64-linux-gnu/crti.o(.debug_line): relocation 1 has invalid symbol index 5
/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crti.o:/build/eglibc-oGUzwX/eglibc-2.19/csu/../sysdeps/x86_64/crti.S:64: first defined here
/tmp/cc8RaCJg.o:(.data+0x0): multiple definition of `server_count'
diner:(.data+0x10): first defined here
/tmp/cc8RaCJg.o:(.data+0x4): multiple definition of `tablea_count'
diner:(.data+0x14): first defined here
/tmp/cc8RaCJg.o:(.data+0x8): multiple definition of `tableb_count'
diner:(.data+0x18): first defined here
/tmp/cc8RaCJg.o:(.data+0xc): multiple definition of `customer_count'
diner:(.data+0x1c): first defined here
/tmp/cc8RaCJg.o:(.data+0x10): multiple definition of `plate_count'
diner:(.data+0x20): first defined here
/tmp/cc8RaCJg.o: In function `eat':
diner4.c:(.text+0x0): multiple definition of `eat'
diner:(.text+0xed): first defined here
/tmp/cc8RaCJg.o: In function `main':
diner4.c:(.text+0x184): multiple definition of `main'
diner:(.text+0x271): first defined here
/usr/lib/gcc/x86_64-linux-gnu/4.8/crtend.o:(.tm_clone_table+0x0): multiple definition of `__TMC_END__'
diner:(.data+0x28): first defined here
/usr/bin/ld: error in diner(.eh_frame); no .eh_frame_hdr table will be created.
collect2: error: ld returned 1 exit status
niu@niu-vb:~/Documents/CSU_OS$ gdb diner
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.3) 7.7.1
Copyright (C) 2014 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
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 diner...(no debugging symbols found)...done.
(gdb) run
Starting program: /home/niu/Documents/CSU_OS/diner
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
starting thread, semaphore is unlocked.
Creating mutex for plate 0
Creating mutex for plate 1
Creating mutex for plate 2
Creating mutex for plate 3
Creating mutex for plate 4
Creating mutex for plate 5
Creating mutex for plate 6
Creating mutex for plate 7
[New Thread 0x7ffff77f6700 (LWP 18606)]
Customer 0 is eating
[New Thread 0x7ffff6ff5700 (LWP 18607)]
Customer 1 is eating
[New Thread 0x7ffff67f4700 (LWP 18608)]
Customer 2 is eating
[New Thread 0x7ffff5ff3700 (LWP 18609)]
Customer 3 is eating
[New Thread 0x7ffff57f2700 (LWP 18610)]
[New Thread 0x7ffff4ff1700 (LWP 18611)]
[New Thread 0x7ffff47f0700 (LWP 18612)]
[New Thread 0x7ffff3fef700 (LWP 18613)]
[New Thread 0x7ffff37ee700 (LWP 18614)]
[New Thread 0x7ffff2fed700 (LWP 18615)]
Customer 0 is finished eating
Customer 1 is finished eating
Customer 2 is finished eating
Customer 3 is finished eating
答案 0 :(得分：1)
这里的整个前提似乎对我来说有点奇怪，因为我从未看到任何会导致任何线程阻塞的争用。尽管如此，我确实看到一个特定的缺陷会导致程序崩溃。
有8个＆＃34;板块＆＃34; （互斥）和10＆＃34;客户＆＃34;这是价值＆＃34; n＆＃34;在你的主题中。
pthread_mutex_lock(&plates[n]);
在n = 7时可以正常工作，然后在n = 8时崩溃，因为它指向无效的内存。
此外 - pthread输入函数的正确原型是void *function(void* arg)（不是int）。您必须将值作为void*传递，然后将其本地转换回int，如果这是您想要的 - 但请注意，这也可能会产生关于截断的编译器警告，因为int是在许多平台上小于void*。
答案 1 :(得分：1)
正如我在评论中所述，您的程序中至少有两个未定义行为的来源：
您尝试使用eat()作为线程启动函数，但它没有正确的类型。线程启动函数必须接受void *类型的单个参数并返回void *，但eat()的参数类型为int。由于参数类型不匹配，您对pthread_create()的调用具有未定义的行为。如果pthread_create()可以被解释为调用指向函数，那么该调用也将具有其自己的未定义行为。
您发送了十个客户主题，每个主题都尝试锁定一个不同的板互斥锁，但只有八个平板互斥锁可用。因此，如果事实上假设eat()接收到您似乎打算要执行的参数值，则必须超出板互斥数组的范围。即使你想象溢出导致操作可访问的内存（无论它实际上是否未定义），内存当然还没有通过pthread_mutex_init()初始化以用作互斥锁。
可能有一个或两个人对你的段错误负责。
您可以创建并使用一堆您不需要的同步对象。 eat()函数的整个主体受信号量server_sem保护，并且您使用该信号量的方式可确保执行该函数的线程永远不会超过一个。因此，互斥体和其他信号量内部的所有用法都没有实际意义 - 对于那些其他同步对象永远不会有任何争用。
当编写eat()时，每个客户线程依次锁定每个表信号量，并在每个信号量的保护下锁定一个板互斥锁。根据您尝试建模的内容，每个客户吃两次，每次一次，但来自同一个盘子。
每个客户线程使用不同的板块（或尝试这样做），因此没有争用板块。没有争用，即使服务器信号量 ，也无需使用互斥锁来保护版访问权。
总的来说，我不清楚你想要建模的互动。如果你不清楚这一点，那么这可能是你的一些困难的原因。我倾向于猜测也许你想要另一个线程代表一个服务器，它将与客户线程合作，将它们分配给可用的座位。即便如此，我还不确定我是否看到了板式互斥体的用途。