指向pthread_create（）的最後一個參數的指針導致崩潰

Question

剛剛遇到了有關如何將第四個參數傳遞給pthread_create（）的奇怪問題。

本來，我寫的代碼如下：

auditLogEntry *newEntry = NULL; 

// malloc and init the memory for newEntry 
rc = audit_init_log_entry(&newEntry); 
// wrapper of 'goto cleanup' 
ERR_IF(rc != 0); 
... 
rc2 = pthread_attr_init(&attr); 
ERR_IF(rc2 != 0); 
rc2 = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED); 
ERR_IF(rc2 != 0); 
rc2 = pthread_create(&syslog_thread, &attr, syslog_thread_handler, (void *)newEntry); 
ERR_IF(rc2 != 0); 
newEntry = NULL; 
... 
cleanup: 
pthread_attr_destroy(&attr); 
if (newEntry != NULL) 
{ 
    audit_free_log_entry(newEntry); 
    newEntry = NULL; 
} 

static void *syslog_thread_handler(void *t) 
{ 
    auditLogEntry *entry = (auditLogEntry *)t; 
    ... // code using entry 
    cleanup: 
    audit_free_log_entry(entry); 

    pthread_exit(0); 
} 

，一切工作正常。

於是，我做了一個變化：

rc2 = pthread_create(&syslog_thread, &attr, syslog_thread_handler, (void *)&newEntry); 
ERR_IF(rc2 != 0); 
... 
cleanup: 
pthread_attr_destroy(&attr); 
if (rc != 0 && newEntry != NULL) 
{ 
    audit_free_log_entry(newEntry); 
    newEntry = NULL; 
} 

static void *syslog_thread_handler(void *t) 
{ 
    auditLogEntry **entry = (auditLogEntry **)t; 
    ... // code using *entry 
    cleanup: 
    audit_free_log_entry(*entry); 
    *entry = NULL; 

    pthread_exit(0); 
} 

線程處理器將使用*進入訪問日誌條目數據，上述變更後。但它沒有奏效。更糟糕的是，流程核心傾倒。

我試過'man pthread_create'，但沒有發現如何將最後一個參數傳遞給它。

我的任何錯誤，在這裏？

Answer 1

您不顯示完整的代碼，因此很難說出發生了什麼。

但是，&newEntry爲您提供了一個指向棧上變量的指針。如果newEntry超出範圍，例如因爲你的函數結束了，你的另一個線程現在有一個無效指針 - 指向堆棧中現在已經消失的地方。並且取消引用這樣的指針會導致未定義的行爲。

int *foo(void) 
{ 
    int x = 2; 
    return &x; 
} 

void bar(void) 
{ 
    int *x = foo(); 
    printf("%d\n", *x); //can't do this, x points to something 
         //on the stack in the foo function, 
         //which isn't valid any more 
} 

你有同樣的問題，如果把foo（）函數傳遞&x給它創建的線程。

void foo(void) 
{ 
    int x = 2; 
    ... 
    pthread_create(&tid, bar, NULL, &x); 
} 

無效*巴（無效* ARG） { INT * X =精氨酸;

printf("%d\n", *x); //same problem here, x points to something 
         //on the stack in the foo function, which isn't valid 
         //if the foo function ends. This concept is exactly the same 
         //if x had been a pointer inside the foo() function. 
} 

這裏也許您的方案：

int globalx = 2; //global variable 
void foo(void) 
{ 
    int *x = malloc(sizeof(int)); 
    ... 

    pthread_create(&tid, bar, NULL, &x); //we're still taking the address of 
             //a local variable. 
} 

void *bar(void *arg) 
{ 
    int **x = arg; 
    printf("%p\n", *x); //still the same problem here, x points to something 
         //on the stack in the foo function, which isn't valid 
} 

Answer 2

無論核心轉儲來自哪裏，都不是來自pthreads。你對最後的論點所做的事絕對沒問題。