我的问题是处理我在linux机器上运行这个程序而不是我自己的mac计算机时出现的分段错误。这个程序运行我相信它应该在我自己的mac计算机上运行，但是当我尝试在学校的linux计算机上运行它时，我得到了一个不会出现在我的mac计算机上的分段错误。我将简要介绍一下这项任务，然后更详细地讨论这个问题。
所以我有这个程序，基本上模拟用一根绳子穿越峡谷的狒狒。只有一只狒狒可以一次穿过，并且对于一次可以穿越的狒狒数量有一定的限制，以及在允许来自另一方向的狒狒被允许穿越之前，有多少狒狒可以从一个方向穿过。代码的实现。
我已经在stackoverflow上搜索了已经存在的分段错误问题，但是大多数都处理多个进程，而我只是使用不同的线程。分段错误最终来自等待不存在的信号量，但当我检查它是否已初始化时，它已成功初始化。同样，这个程序在我的Mac上工作，但是当我尝试在我的Mac上运行它时，它不起作用。任何帮助都可以理解为什么它不能在linux机器上运行但可以在mac上运行。如果需要更多信息，我很乐意提供。我在某一点上进行了错误检查，但该代码已从学校计算机上删除。据我记得，我的错误检查没有显示任何错误。
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
#include <sys/time.h>
#include <time.h>
#include <pthread.h>
#include <semaphore.h>
#include <fcntl.h>
#include <sys/stat.h> //for mode flags, if needed for future use
#define ATOB_COUNT 20
#define BTOA_COUNT 20
#define RANDOM_SEED 2123
//semaphore names
#define MUTEX_SEM "/mutex"
#define TOB_SEM "/toB"
#define TOA_SEM "/toA"
//define methods here if needed
void *toAThread(void *threadId);
void *toBThread(void *threadId);
void my_sleep(int limit);
void sem_open_errorCheck(char *name, unsigned int startingValue, sem_t *result);
//defining semaphores and shared variables
sem_t *mutex, *toB, *toA;
int xingCount = 0;
int xedCount = 0;
int toBWaitCount = 0;
int toAWaitCount = 0;
enum xingDirectionTypes {
none,
aToB,
bToA
};
enum xingDirectionTypes xingDirection = none;
char orderLeaving[100];
struct threadInfo {
int threadId;
};
struct threadInfo atobIDs[ATOB_COUNT];
struct threadInfo btoaIDs[BTOA_COUNT];
int main(void) {
pthread_t atobPTHREADS[ATOB_COUNT];
pthread_t btoaPTHREADS[BTOA_COUNT];
pthread_attr_t attr;
void *status;
srandom(RANDOM_SEED);
//call helper method which creates semaphore and errorchecks
sem_open_errorCheck(MUTEX_SEM, (unsigned int)1, mutex);
sem_open_errorCheck(TOA_SEM, (unsigned int)0, toA);
sem_open_errorCheck(TOB_SEM, (unsigned int)0, toB);
//Creating a set of attributes to send to the threads
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
//spawn toB baboons
int counter;
for (counter = 0; counter < BTOA_COUNT; counter++) {
atobIDs[counter].threadId = counter;
int result;
if ((result = pthread_create(&atobPTHREADS[counter], &attr, toBThread, (void*) &atobIDs[counter])) == -1) {
perror("Thread Creation Error: atob baboon");
exit(EXIT_FAILURE);
}
}
//spawn toA baboons
for (counter = 0; counter < ATOB_COUNT; counter++) {
btoaIDs[counter].threadId = counter + 20;
int result;
if ((result = pthread_create(&btoaPTHREADS[counter], &attr, toAThread, (void*) &btoaIDs[counter])) == -1) {
perror("Thread Creation Error: btoa baboon");
exit(EXIT_FAILURE);
}
}
//Wait for all the threads to finish
for(counter = 0; counter < ATOB_COUNT; counter++)
{
int result = pthread_join(atobPTHREADS[counter], &status);
if(result == -1)
{
perror("Thread Join: AtoB");
exit(EXIT_FAILURE);
}
}
for(counter = 0; counter < BTOA_COUNT; counter++)
{
int result = pthread_join(btoaPTHREADS[counter], &status);
if(result == -1)
{
perror("Thread Join: BtoA");
exit(EXIT_FAILURE);
}
}
printf("The order leaving %s", orderLeaving);
exit(EXIT_SUCCESS);
}
void *toBThread(void *threadId) {
struct threadInfo *info;
info = (struct threadInfo *)threadId;
int id = info->threadId;
my_sleep(100); //simulate being idle for 1-100ms
//for order checking
char *baboonOrder;
baboonOrder = "B ";
strcat(orderLeaving, baboonOrder);
sem_wait(mutex);
if ((xingDirection == aToB || xingDirection == none) && xingCount < 5 && (xedCount + xingCount) < 10) { //there is an extra parenthesis here in the solutions
xingDirection = aToB;
xingCount++;
printf("AtoB baboon (thread %d) got on the rope\n", id);
sem_post(mutex);
}
else {
toBWaitCount++;
sem_post(mutex);
sem_wait(toB);
toBWaitCount--;
xingCount++;
xingDirection = aToB;
printf("AtoB baboon (thread %d) got on the rope\n", id);
sem_post(mutex);
}
//CROSSING
sem_wait(mutex);
printf("AtoB baboon (thread %d) got off the rope\n", id);
xedCount++;
xingCount--;
if (toBWaitCount != 0 && (((xedCount+xingCount)<10) || ((xedCount+xingCount) >= 10 && toAWaitCount == 0))) {
sem_post(toB);
}
else {
if (xingCount == 0 && toAWaitCount != 0 && (toBWaitCount == 0 || (xedCount + xingCount)>=10)) {
xingDirection = bToA;
xedCount = 0;
sem_post(toA);
}
else {
if (xingCount == 0 && toBWaitCount == 0 && toAWaitCount == 0) {
xingDirection = none;
xedCount = 0;
sem_post(mutex);
}
else {
sem_post(mutex);
}
}
}
}
/*
baboons going from side a to side b
*/
void *toAThread(void *threadId) {
struct threadInfo *info;
info = (struct threadInfo *)threadId;
int id = info->threadId;
my_sleep(100);
//for order checking
char *baboonOrder;
baboonOrder = "A ";
strcat(orderLeaving, baboonOrder);
sem_wait(mutex);
if ((xingDirection == bToA || xingDirection == none) && xingCount < 5 && (xedCount + xingCount) < 10) { //there is an extra parenthesis here in the solutions
xingDirection = bToA;
xingCount++;
printf("BtoA baboon (thread %d) got on the rope\n", id);
sem_post(mutex);
}
else {
toAWaitCount++;
sem_post(mutex);
sem_wait(toA);
toAWaitCount--;
xingCount++;
xingDirection = bToA;
printf("BtoA baboon (thread %d) got on the rope\n", id);
sem_post(mutex);
}
//CROSSING
sem_wait(mutex);
printf("BtoA baboon (thread %d) got off the rope\n", id);
xedCount++;
xingCount--;
if (toAWaitCount != 0 && (((xedCount+xingCount)<10) || ((xedCount+xingCount) >= 10 && toBWaitCount == 0))) {
sem_post(toA);
}
else {
if (xingCount == 0 && toBWaitCount != 0 && (toAWaitCount == 0 || (xedCount + xingCount)>=10)) {
xingDirection = aToB;
xedCount = 0;
sem_post(toB);
}
else {
if (xingCount == 0 && toAWaitCount == 0 && toBWaitCount == 0) {
xingDirection = none;
xedCount = 0;
sem_post(mutex);
}
else {
sem_post(mutex);
}
}
}
}
//taken with permission from readers/writers problem
//Puts the calling thread to sleep to simulate both random start times and random workloads
void my_sleep(int limit) {
struct timespec time_ns;
int duration = random() % limit + 1;
time_ns.tv_sec = 0;
time_ns.tv_nsec = duration * 1000000;
int result = nanosleep(&time_ns, NULL);
if (result != 0)
{
perror("Nanosleep");
exit(EXIT_FAILURE);
}
}
void sem_open_errorCheck(char *name, unsigned int startingValue, sem_t *result) {
sem_unlink(name);
result = sem_open(name, O_CREAT, 0600, startingValue);
if (result == -1) {
perror("sem_open error: semaphore failed to open correctly");
exit(EXIT_FAILURE);
}
}
答案 0 :(得分：8)
调试此方法的最佳方法是使用gdb调试程序运行它。像这样：
gdb my-monkey-program
(gdb) run
Program received signal SIGSEGV, Segmentation fault.
(gdb) info threads
(gdb) bt
另一个好主意是用valgrind运行它：
valgrind ./my-monkey-program
将告诉您无效的内存访问和各种事情。
gdb报告调用堆栈是：
#0 sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:45
#1 0x0000000000400e8d in toAThread (threadId=0x602160) at test.c:190
#2 0x00007ffff7bc4e9a in start_thread (arg=0x7fffed7e9700) at pthread_create.c:308
#3 0x00007ffff78f1cbd in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
#4 0x0000000000000000 in ?? ()
以下是我编译的行号：
187 baboonOrder = "A ";
188 strcat(orderLeaving, baboonOrder);
189
190 sem_wait(mutex);
这是因为mutex为NULL。
您实际上从未真正分配到mutex变量。您将指针传递给sem_open_errorCheck，但您真正需要传递的是指向指针的指针。据推测，这同样适用于toA和toB。
它只是运气，它在Mac上运行了！