我试图找到当我在涉及系统功能时尝试生成Signal（^ C）时发生的分段错误错误的原因。
另外，我试图理解为什么我只看到一个打印Thread1 cancelled而不是所有三个线程的3个打印件？ [Corrected the code for this point]
以下是testapp.c的代码。这是我为测试my utility program而做的一种压力测试应用程序。该实用程序不是我正在使用的实际程序，而是演示其中使用的信号量。它正在使用system()函数执行我的实用程序。
下面列出了源代码和输出，
/******* testapp.c *****************/
/* gcc testapp.c -o testapp -pthread */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#include <signal.h>
#include <errno.h>
#define SLEEP1 250
#define SLEEP2 250
#define SLEEP3 250
pthread_t thread1;
pthread_t thread2;
pthread_t thread3;
static volatile sig_atomic_t isRunning = 1;
void signal_handler(int signal)
{
int rc = 0;
switch (signal)
{
case SIGINT:
case SIGTERM:
case SIGQUIT:
printf("Signal generated, cancelling threads...");
// Graceful shutdown
//isRunning = 0; //commented to see the segmentation fault issue
rc = pthread_cancel(thread1);
if(rc != 0){
printf("signal_handler:pthread_cancel-1 failed - %d (%m)\n", errno);
}
printf("Thread1 cancelled\n");
rc = pthread_cancel(thread2);
if(rc != 0){
printf("signal_handler:pthread_cancel-2 failed - %d (%m)\n", errno);
}
printf("Thread2 cancelled\n");
rc = pthread_cancel(thread3);
if(rc != 0){
printf("signal_handler:pthread_cancel-3 failed - %d (%m)\n", errno);
}
printf("Thread3 cancelled\n");
break;
default:
break;
}
}
void* thread1_worker(void* data)
{
struct timeval timeout;
int ret = 0;
do
{
printf("Requesting cmd1\n");
ret = system("util -c:cmd1 -v 2>> /tmp/stderr.log");
timeout.tv_sec = 0;
timeout.tv_usec = SLEEP1 * 1000; //milliseconds
ret = select(0, NULL, NULL, NULL, &timeout);
}while(isRunning);
printf("Exiting thread1...");
pthread_exit((void*)0);
}
void* thread2_worker(void* data)
{
struct timeval timeout;
int ret = 0;
do
{
printf("Requesting cmd2\n");
ret = system("util -c:cmd2 -v 2>> /tmp/stderr.log");
timeout.tv_sec = 0;
timeout.tv_usec = SLEEP2 * 1000; //milliseconds
int ret = select(0, NULL, NULL, NULL, &timeout);
}while(isRunning);
printf("Exiting thread2...");
pthread_exit((void*)0);
}
void* thread3_worker(void* data)
{
struct timeval timeout;
int ret = 0;
do
{
printf("Requesting cmd3\n");
ret = system("util -c:cmd3 -v 2>> /tmp/stderr.log");
timeout.tv_sec = 0;
timeout.tv_usec = SLEEP3 * 1000; //milliseconds
int ret = select(0, NULL, NULL, NULL, &timeout);
}while(isRunning);
printf("Exiting thread3...");
pthread_exit((void*)0);
}
int main(int argc, char **argv){
signal(SIGTERM, signal_handler);
signal(SIGINT, signal_handler);
signal(SIGQUIT, signal_handler);
printf("Starting threads...\n");
pthread_create(&thread1, NULL, thread1_worker, (void*) NULL);
pthread_create(&thread2, NULL, thread2_worker, (void*) NULL);
pthread_create(&thread3, NULL, thread3_worker, (void*) NULL);
pthread_join(thread1, NULL);
pthread_join(thread2, NULL);
pthread_join(thread3, NULL);
return 0;
}
输出如下，方括号中的打印件是程序的实际输出而不是上面的util程序，
root@mydevice:~$ testapp
Starting threads...
Requesting cmd1
Requesting cmd2
Requesting cmd3
cmd2:[05 05]
cmd1:[0]
cmd3:[00 00 00 00 00 ]
Requesting cmd2
Requesting cmd1
cmd2:[05 05]
Requesting cmd3
cmd1:[1]
cmd3:[00 00 00 00 00 ]
Requesting cmd2
Requesting cmd1
cmd2:[05 05]
Requesting cmd3
cmd1:[2]
cmd3:[00 00 00 00 00 ]
Requesting cmd2
Requesting cmd1
cmd2:[05 05]
Requesting cmd3
cmd1:[3]
cmd3:[00 00 00 00 00 ]
Requesting cmd2
Requesting cmd1
cmd2:[05 05]
Requesting cmd3
^Ccmd1:[4]
sh: line 1: 964 Segmentation fault util -c:cmd3 -v 2>> /tmp/stderr.log
Requesting cmd2
cmd2:[05 05]
Requesting cmd1
Requesting cmd3
cmd1:[5]
cmd3:[00 00 00 00 00 ]
Requesting cmd2
cmd2:[05 05]
Requesting cmd1
Requesting cmd3
cmd3:[00 00 00 00 00 ]
Requesting cmd2
cmd1:[84213760]
Requesting cmd3
^Ccmd2:[00 00] -----------------------------------------------> Signal
cmd3:[00 00 00 00 00 ]
Requesting cmd1
cmd1:[7]
Requesting cmd2
Requesting cmd3
cmd2:[05 05]
cmd3:[00 00 00 00 00 ]
Requesting cmd1
cmd1:[8]
^CSignal generated, cancelling threads...Thread1 cancelled ---->Signal
Segmentation fault
root@mydevice:~$
答案 0 :(得分：3)
这只是一个“错字”错误。
变化：
pthread_create(&thread1, NULL, thread1_worker, (void*) NULL);
pthread_create(&thread1, NULL, thread2_worker, (void*) NULL);
pthread_create(&thread1, NULL, thread3_worker, (void*) NULL);
分为：
pthread_create(&thread1, NULL, thread1_worker, (void*) NULL);
pthread_create(&thread2, NULL, thread2_worker, (void*) NULL);
pthread_create(&thread3, NULL, thread3_worker, (void*) NULL);
答案 1 :(得分：1)
根据评论结果纠正代码：
/******* testapp.c *****************/
/* gcc testapp.c -o testapp -pthread */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <pthread.h>
#include <signal.h>
#include <errno.h>
#define SLEEP1 250
#define SLEEP2 250
#define SLEEP3 250
pthread_t thread1;
pthread_t thread2;
pthread_t thread3;
static volatile sig_atomic_t isRunning = 1;
void signal_handler(int signal)
{
int rc = 0;
char buffer[1024];
switch (signal)
{
case SIGINT:
case SIGTERM:
case SIGQUIT:
write( 1, "Signal generated, cancelling threads...\n");
// Graceful shutdown
//isRunning = 0; //commented to see the segmentation fault issue
rc = pthread_cancel(thread1);
if( rc )
{
write(1, "signal_handler:pthread_cancel-1 failed\n" ):
}
write( 1, "Thread1 cancelled\n");
rc = pthread_cancel(thread2);
if( rc )
{
write( 1, "signal_handler:pthread_cancel-2 failed\n");
}
write( 1, "Thread2 cancelled\n");
rc = pthread_cancel(thread3);
if( rc )
{
write( 1, "signal_handler:pthread_cancel-3 failed\n");
}
"Thread3 cancelled\n");
break;
default:
break;
} // end switch
} // end function: signal_handler
void* thread1_worker(void* data)
{
struct timeval timeout;
int ret = 0;
(void)data;
do
{
printf("Requesting cmd1\n");
ret = system("util -c:cmd1 -v 2>> /tmp/stderr.log");
if( ret )
{
perror( "system-util result" );
}
timeout.tv_sec = 0;
timeout.tv_usec = SLEEP1 * 1000; //milliseconds
select(0, NULL, NULL, NULL, &timeout);
} while(isRunning);
printf("Exiting thread1...\n");
pthread_exit( NULL );
} // end function: thread1_worker
void* thread2_worker(void* data)
{
struct timeval timeout;
int ret = 0;
(void)data;
do
{
printf("Requesting cmd2\n");
ret = system("util -c:cmd2 -v 2>> /tmp/stderr.log");
if( ret )
{
perror( "system-util result" );
}
timeout.tv_sec = 0;
timeout.tv_usec = SLEEP2 * 1000; //milliseconds
select(0, NULL, NULL, NULL, &timeout);
}while(isRunning);
printf("Exiting thread2...\n");
pthread_exit((void*)0);
} // end function: thread2_worker
void* thread3_worker(void* data)
{
struct timeval timeout;
int ret = 0;
(void)data;
do
{
printf("Requesting cmd3\n");
ret = system("util -c:cmd3 -v 2>> /tmp/stderr.log");
if( ret )
{
perror( "system-util result" );
}
timeout.tv_sec = 0;
timeout.tv_usec = SLEEP3 * 1000; //milliseconds
select(0, NULL, NULL, NULL, &timeout);
}while(isRunning);
printf("Exiting thread3...\n");
pthread_exit((void*)0);
} // end function: thread3_worker
int main( void )
{
signal(SIGTERM, signal_handler);
signal(SIGINT, signal_handler);
signal(SIGQUIT, signal_handler);
printf("Starting threads...\n");
pthread_create(&thread1, NULL, thread1_worker, (void*) NULL);
pthread_create(&thread2, NULL, thread2_worker, (void*) NULL);
pthread_create(&thread3, NULL, thread3_worker, (void*) NULL);
pthread_join(thread1, NULL);
pthread_join(thread2, NULL);
pthread_join(thread3, NULL);
return 0;
} // end function: main
运行代码时，以下输出是典型的:(继续重复，语句顺序略有不同：
system-util result: Success
system-util result: Success
system-util result: Success
Requesting cmd3
Requesting cmd2
Requesting cmd1
然后，由于我没有util函数，/tmp/stderr.log包含以下重复语句：
sh: 1: util: not found
sh: 1: util: not found
sh: 1: util: not found
sh: 1: util: not found
sh: 1: util: not found
sh: 1: util: not found
sh: 1: util: not found
sh: 1: util: not found
并且，除非util函数标记为executable并且在此程序中位于同一目录中，否则它将失败。
将util更改为./util，如果在同一目录中，则无需将其标记为executable
seg fault事件很可能来自util函数，而不是来自发布的代码。
应该进一步考虑调用函数：signal()，每个手册页都不可靠。该手册页强烈建议使用：sigaction()代替。