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Missing or double initialization of thread attribute

Duplicated initialization of thread attributes or noninitialized thread attribute used in functions that expect initialized attributes

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Description

This defect occurs during one of these situations:

  • You initialize a thread attribute twice with a function such as pthread_attr_init without an intermediate call to a function such as pthread_attr_destroy.

    The function pthread_attr_destroy destroys a thread attribute object and enables the system to reclaim resources associated with the object.

  • You use a noninitialized thread attribute in a function such as pthread_create, which expects an initialized attribute. A thread attribute might be noninitialized because it was never initialized previously or destroyed with the pthread_attr_destroy function.

    Noninitialized thread attributes are detected for all functions in the POSIX® standard.

The Result Details pane describes whether the attribute is doubly initialized or noninitialized and also shows previous related events.

Note that a thread attribute is considered initialized only if the call to pthread_attr_init is successful. For instance, the thread attribute is not initialized in the if branch here:

pthread_attr_t attr;
int thread_success;

thread_success = pthread_attr_init(&attr);
if(thread_success != 0) {
   /* Thread attribute considered noninitialized */
}
The issue is also flagged if you do not check the return value from a call to pthread_attr_init.

Risk

Initializing a thread attribute without destroying the previously initialized attribute or using noninitialized thread attributes leads to undefined behavior.

Fix

Before using a thread attribute, initialize the attribute by using the pthread_attr_init function.

pthread_attr_t attr;
int thread_success;

/* Initialize attribute */
thread_success = pthread_attr_init(&attr);
if(thread_success != 0) {
   /* Handle initialization error */
}
...
/* Use attribute */
thread_success = pthread_create(&thr, &attr, &thread_start, NULL);
After initialization, destroy a thread attribute by using pthread_attr_destroy before initializing again:
pthread_attr_t attr;
int thread_success;

/* Destroy attribute */
thread_success = pthread_attr_destroy(&attr);
if(thread_success != 0) {
   /* Handle destruction error */
}
...
/* Reinitialize attribute */
thread_success = pthread_attr_init(&attr);

Examples

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#include <stddef.h>
#include <pthread.h>
#define thread_success 0

extern void *thread_func(void *arg);


int main() {
    pthread_t id;
    pthread_attr_t attr;
    
    if(thread_success == pthread_create(&id, &attr, thread_func, NULL)) {
    }

    return 0;    
}

In this example, the attribute attr is not initialized before its use in the pthread_create call.

Correction – Initialize Thread Attribute Before Use

Before using a thread attribute in the pthread_create function, initialize the attribute with the pthread_attr_init function.

#include <stddef.h>
#include <pthread.h>
#define thread_success 0

extern void *thread_func(void *arg);

int main() {
    pthread_t id;
    pthread_attr_t attr;
    
    if(thread_success != pthread_attr_init(&attr)) {
        return 0;
    }
   
    if(thread_success == pthread_create(&id, &attr, thread_func, NULL)) {
    }
    
    return 0;    
}
#include <stddef.h>
#include <pthread.h>
#define thread_success 0

extern void *thread_func(void *arg);

int main() {
    pthread_t id;
    pthread_attr_t attr;
    
    pthread_attr_init(&attr);
   
    if(thread_success == pthread_create(&id, &attr, thread_func, NULL)) {
    }
    
    return 0;    
}

In this example, the return value of pthread_attr_init is not checked. If the thread attribute initialization fails, the error does not get handled. A possibly undefined thread attribute is later used in the pthread_create function.

Correction – Handle Errors from Thread Attribute Initialization

One possible correction is to use the thread attribute only if the return value from pthread_attr_init indicates successful initialization.

#include <stddef.h>
#include <pthread.h>
#define thread_success 0

extern void *thread_func(void *arg);

int main() {
    pthread_t id;
    pthread_attr_t attr;
    
    if(thread_success != pthread_attr_init(&attr)) {
        return 0;
    }
   
    if(thread_success == pthread_create(&id, &attr, thread_func, NULL)) {
    }
    
    return 0;    
}

Result Information

Group: Concurrency
Language: C
Default: Off
Command-Line Syntax: BAD_THREAD_ATTRIBUTE
Impact: Medium

Version History

Introduced in R2019b

See Also

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