• C

Threadsafe alternatives to log4c that support logging in microseconds

Hi guys,

Again, as per title. I need a logging solution that's thread safe and supports logging in microseconds.....
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phoffricConnect With a Mentor Commented:
Couldn't you wrap the useful features of log4c with a mutex (just be careful that one log4c function doesn't call another that is wrapped with the same mutex). Or to do it without analysis, you could have a distinct mutex per log4c function. And then you just call your log4c_ts functions.
From previous question, you already have a function that can do the logging with microseconds. To make this function thread-safe, you can add take a mutex at the entry point of the function, and release the mutex at the exit point.

Below is code that shows how to use a mutex to protect your function. Code is taken from

// ************* short example *******************
/* Note scope of variable and mutex are the same */
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
int counter=0;

/* Function C */
void functionC()
   pthread_mutex_lock( &mutex1 );
   pthread_mutex_unlock( &mutex1 );

// ******************** A sample Program ***********************

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

void *functionC();
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
int  counter = 0;

   int rc1, rc2;
   pthread_t thread1, thread2;

   /* Create independent threads each of which will execute functionC */

   if( (rc1=pthread_create( &thread1, NULL, &functionC, NULL)) )
      printf("Thread creation failed: %d\n", rc1);

   if( (rc2=pthread_create( &thread2, NULL, &functionC, NULL)) )
      printf("Thread creation failed: %d\n", rc2);

   /* Wait till threads are complete before main continues. Unless we  */
   /* wait we run the risk of executing an exit which will terminate   */
   /* the process and all threads before the threads have completed.   */

   pthread_join( thread1, NULL);
   pthread_join( thread2, NULL); 


void *functionC()
   pthread_mutex_lock( &mutex1 );
   printf("Counter value: %d\n",counter);
   pthread_mutex_unlock( &mutex1 );

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PMembreyAuthor Commented:
this is what I have now, I was just hoping that there might be a more featureful solution already available.
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I don't know how complex or the performance requirements of your system is. But in one highly real-time system, having each task do its own logging resulted in unacceptable degradation of the system. So, instead, the architects just added a logging task which accepted messages in its queue. With this approach, there were naturally no thread-safe issues. This logging task did the time-stamping so that the real-time tasks didn't need the extra overhead. The time-stamping results were sufficient for our needs even though they may be a ms off.
FYI - I came across this link on log4cplus which says the package is thread-safe.
In your other question (http://www.experts-exchange.com/Programming/Languages/C/Q_26479755.html), it was mentioned how to use log4c in a thread safe way.

I'm curious though : are you sure you really need microsecond precision logs ? That's rarely useful, especially because the logging operation itself will likely take much more than a few microseconds.

I mentioned it in one of your other questions too : if you really need a micro-second-precision timer (from the start of the executable generally) mentioned in the logs, you can always add it. Nothing prevents you from doing that.
A micro-second precision timestamp (with date and time of day) though is a very different matter. Very few systems support something like that.

So, you might want to re-consider this ;)
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