C and C++ Binaries

CONCURRENCY.TL : Try-lock that will never succeed

Summary

A try-lock on a mutex that has already been locked with no intervening unlock.

Properties

Class Name Try-lock that will never succeed
Significance reliability
Mnemonic CONCURRENCY.TL
Categories
CWE CWE:413 Improper Resource Locking
CERT-CPP CERT-CPP:CON56-CPP Do not speculatively lock a non-recursive mutex that is already owned by the calling thread
Availability Available for C and C++.
Enabling Checks for this warning class are enabled by default. To disable them, add the following WARNING_FILTER rule to the project configuration file. 
WARNING_FILTER += discard class="Try-lock that will never succeed"

Example 

#include <pthread.h>
#include <stdlib.h>

void concurrency_tl_bad(void){
    pthread_mutex_t mut;
    if( pthread_mutex_init( &mut, NULL ) !=  0 ) abort();
    if( pthread_mutex_lock( &mut ) != 0 ) abort();
    if( pthread_mutex_trylock( &mut ) != 0 ) abort(); /* 'Try-lock that will never succeed' warning issued here
                                                       * - &mut is already locked by the previous call
                                                       * - execution will never reach the following line
                                                       */
    if( pthread_mutex_unlock( &mut ) != 0 ) abort();
    if( pthread_mutex_destroy( &mut ) != 0 ) abort();
}

void concurrency_tl_ok(void){
    pthread_mutex_t mut;
    if( pthread_mutex_init( &mut, NULL ) !=  0 ) abort();
    if( pthread_mutex_trylock( &mut ) != 0 ) abort();                   /* ok: &mut is not already locked */
    if( pthread_mutex_unlock( &mut ) != 0 ) abort();
    if( pthread_mutex_destroy( &mut ) != 0 ) abort();
}

Triggering Functions

CodeSonar ships with library models that allow it to recognize a number of try-lock functions, across many different libraries. Some examples are shown in the table below. If one of these functions is called when the mutex is always already locked, a warning will be issued.

If you have created a custom library model for some function f() in terms of one of these existing models, calls to f() will also be capable of triggering Try-lock that will never succeed warnings.

Functions that can trigger warnings include...
Apache Portable Runtime (APR) apr_global_mutex_trylock()
libc pthread_mutex_trylock()
Linux Kernel down_trylock()
Mac OS X hw_lock_try()
OpenMP omp_test_lock()
Qt QMutex::tryLock()
VxWorks semBCreate()
Win32 TryEnterCriticalSection()
wxWidgets wxMutex::TryLock()

Notes

This warning indicates a redundant (and potentially misleading) program statement.

Relevant Configuration File Parameters

The following configuration file parameters affect checks for this warning class.