conflict with google flags library

[woonhak]

If an application uses google flags,
the call pthread_mutex_init invokes segment fault.

• Env
  Ubuntu 14.04
  libgflags-dev 2.0-1.1ubuntu1
  gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3)

• Topology
  #define NUMA_NODES 4
  #define CPU_NUMBER 64
  #define L_CACHE_LINE_SIZE 128
  #define PAGE_SIZE 4096

Following is a simple example:

example.cc

#include <iostream>                                                                      
#include <gflags/gflags.h>                                                               
#include <pthread.h>                                                                     
                                                                                         
DEFINE_bool(verbose, false, "Display program name before message");                      
DEFINE_string(message, "Hello world!", "Message to print");                              
                                                                                         
                                                                                         
int main(int argc, char **argv)                                                          
{                                                                                        
        static pthread_mutex_t mutex;                                                    
        google::ParseCommandLineFlags(&argc, &argv, true);                               
        pthread_mutex_init(&mutex, NULL);                                                
                                                                                         
        if (FLAGS_verbose) std::cout << google::ProgramInvocationShortName() << ": ";    
        std::cout << FLAGS_message << std::endl;                                         
        google::ShutDownCommandLineFlags();                                              
                                                                                         
        pthread_mutex_destroy(&mutex);                                                   
                                                                                         
        return 0;                                                                        
}                                                                                        

---

• build
  g++ -o example example.cc -lgflags -lpthread

• run
  /path/to/litl/lib{lock}_{waiting_policy} ./example
  -> segment fault

• reason
  call (REAL)(pthread_mutex_init) failed,
  because real_pthread_mutex_init_{lock} is NULL and not correctly linked.

[woonhak]

I found what is the problem.

if rwlock_init called before previous lock variable not unlocked,
then clht can't find previous lock object.

Following example1.cc always dead because of this problem.

#include <iostream>
#include <pthread.h>
                                                 

int main(int argc, char **argv)
{
        static pthread_rwlock_t rwlock, rwlock1;
        pthread_rwlock_init(&rwlock, NULL);
        pthread_rwlock_wrlock(&rwlock);

        pthread_rwlock_init(&rwlock1, NULL);
        pthread_rwlock_wrlock(&rwlock1);
       
       //segment fault at following line
        pthread_rwlock_unlock(&rwlock);
        pthread_rwlock_unlock(&rwlock1);

        pthread_rwlock_destroy(&rwlock);
        pthread_rwlock_destroy(&rwlock1);

        std::cout<<"done"<<std::endl;
        return 0;
}

[HugoGuiroux]

Hi @woonhak,

Thanks for discovering this bug. I pushed a fix that should avoid the crashes (at least on your two examples). Can you please test with the latest master version and tell me if it's OK?

[woonhak]

You fixed this issue exactly what I thought
It works fine now.
Thanks for the fix.