似乎无法在此C分配上取得任何进展，希望有人立即发现问题：目标是使用POSIX消息队列实现线程池。线程在启动时创建，然后在消息队列中的任务之后接收任务。线程应该接收一个16字节的 task_t 类型的结构，它包含该函数以及指向它应该执行的参数的指针。
一旦线程处理了第一个任务，即在执行函数 foo 时，我会得到一个分段错误，可以在threadPoolFun中访问 task_ptr-＆gt; func < / em>并且应该使用参数 task_ptr-＆gt;这个运行：
void * threadPoolFun(void * arg) {
task_t * task_ptr;
int size = attr.mq_msgsize; //size = 16
char buf[size];
while (1) {
int ret_val = mq_receive(task_queue, buf, size, NULL);
if (ret_val == -1) {
perror("Error receiving message: ");
}
task_ptr = (task_t *) buf;
if (task_ptr->func == NULL) {
break;
}
task_ptr->func(task_ptr->this);
}
return NULL;
}
分段错误：
Program terminated with signal SIGSEGV, Segmentation fault. #0 0x000000000040086a in foo (arg=0x7ffdd71fdfd0) at all_in_one.c:37 37 td->retVal = (double) td->tid; [Current thread is 1 (Thread 0x7fec2d544700 (LWP 9853))] (gdb) list 32 fooTask_t; // type for this tasks 33 34 //definition of task: write tid to retVal 35 void foo(void * arg) { 36 fooTask_t *td = (fooTask_t *) arg; 37 td->retVal = (double) td->tid; 38 } 39 40 // initialize task 41 void fooInit(fooTask_t * t) { (gdb) backtrace #0 0x000000000040086a in foo (arg=0x7ffdd71fdfd0) at all_in_one.c:37 #1 0x0000000000400b8c in threadPoolFun (arg=0x0) at all_in_one.c:118 #2 0x00007fec2f1196ba in start_thread (arg=0x7fec2d544700) at pthread_create.c:333 #3 0x00007fec2ee4f41d in clone ()
完整代码：
#include <mqueue.h>
#include <pthread.h>
#include <stdio.h>
//number of threads
#define NTH 4
//number of tasks
#define NTASKS 10
void * threadPoolFun(void * arg);
typedef void( * taskfun_t)(void * );
//minimal task data structure: func to be executed with args this, abstraction from actual task
typedef struct minTaskDataStruct {
void * this;
taskfun_t func;
}
task_t;
//data structure for actual task
typedef struct fooDataStruct {
// mandatory entries
void * this; // pointer to this structure
taskfun_t func; // function with signature: void foo(void *)
// data for individual task instances
long tid; // task id
double retVal; // return value
}
fooTask_t; // type for this tasks
//definition of task: write tid to retVal
void foo(void * arg) {
fooTask_t *td = (fooTask_t *) arg;
td->retVal = (double) td->tid;
}
// initialize task
void fooInit(fooTask_t * t) {
t-> this = t; // set this pointer
t-> func = foo; // set task function
}
//data structure for threads
pthread_t th[NTH];
//data structure for task queue attributes
static struct mq_attr attr;
//task queue
mqd_t task_queue;
//create task structs and store them in array td
fooTask_t td[NTASKS];
int main() {
printf("Setting up tasks\n");
for (int i = 0; i < NTASKS; i++) {
fooTask_t task;
task.tid = i;
fooInit(&task);
td[i] = task;
}
// set attributes
attr.mq_flags = 0; /* Flags: 0 or O_NONBLOCK */
attr.mq_maxmsg = 10; /* Max. # of messages on queue */
attr.mq_msgsize = 16; /* Max. message size (bytes) */
printf("Opening task queue\n");
// set up task queue
task_queue = mq_open("/my_task_queue_mq", O_CREAT | O_RDWR, 0700, & attr);
//create threads with default attributes, pass threadpool function
//threads will run as long as func passed to them is not NULL
for (long i = 0; i < NTH; i++) {
printf("Creating thread %ld\n", i);
pthread_create( & th[i], NULL, threadPoolFun, NULL);
}
//send tasks to queue, tasks to be consumed by threads, only send first 16 bytes
for (int i = 0; i < NTASKS; i++) {
printf("Sending task %d\n", i);
mq_send(task_queue, (const char * ) &td[i], sizeof(task_t), 0);
}
//send dummy tasks with func==NULL to terminate threads
for (int i = 0; i < NTASKS; i++) {
printf("Sending dummy task %d\n", i);
task_t dummy_task;
dummy_task.this = & dummy_task;
dummy_task.func = NULL;
mq_send(task_queue, (const char * ) & dummy_task, sizeof(task_t), 0);
}
//verify task execution
int sum1 = 0;
int sum2 = 0;
for (int i = 0; i < NTASKS; i++) {
sum1 += td[i].retVal;
sum2 += i;
}
if (sum1 == sum2) {
printf("Success: Sum1 %d equals Sum2 %d", sum1, sum2);
} else {
printf("Fail: Sum1 %d does not Sum2 %d", sum1, sum2);
}
return 0;
}
//threadPoolFun function definition
void * threadPoolFun(void * arg) {
task_t * task_ptr;
int size = attr.mq_msgsize; //size = 16
char buf[size];
while (1) {
int ret_val = mq_receive(task_queue, buf, size, NULL);
if (ret_val == -1) {
perror("Error receiving message: ");
}
task_ptr = (task_t *) buf;
if (task_ptr->func == NULL) {
break;
}
task_ptr->func(task_ptr->this);
}
return NULL;
}
感谢任何帮助，非常感谢提前！ 劳伦斯
答案 0 :(得分：0)
问题在于，在堆栈中的对象不再存在后，您可以使用地址。你有这个：
for (int i = 0; i < NTASKS; i++) {
fooTask_t task;
task.tid = i;
fooInit(&task);
td[i] = task;
}
&task就是这样一个指针。这很容易修复，因为您已经有一个存储任务的地方。这是更好的代码：
for (int i = 0; i < NTASKS; i++) {
fooTask_t task;
task.tid = i;
td[i] = task;
fooInit(&td[i]);
}
发生这种情况的第二个地方是：
for (int i = 0; i < NTASKS; i++) {
printf("Sending dummy task %d\n", i);
task_t dummy_task;
dummy_task.this = & dummy_task;
dummy_task.func = NULL;
mq_send(task_queue, (const char * ) & dummy_task, sizeof(task_t), 0);
}
由于虚拟任务不需要在任何地方单独保存，因此您可以移出dummy_task的声明，因此它将在main的整个执行过程中生效：
task_t dummy_task;
dummy_task.this = & dummy_task;
dummy_task.func = NULL;
//send dummy tasks with func==NULL to terminate threads
for (int i = 0; i < NTASKS; i++) {
fprintf(stderr, "Sending dummy task %d\n", i);
mq_send(task_queue, (const char * ) & dummy_task, sizeof(task_t), 0);
}
在此之后，您的算法仍然存在同步问题，但这是一个单独的问题，我留给您。
我将打印从stdout更改为stderr，因为前者是缓冲的，并且在程序崩溃时丢失了。