Question

I have written a small server application. It stores a lot of data in strings. When stresstesting it, RSS memory grows (spotted by $top).

I have ran the program through “Instrument” – Mac OS X memory leak applicaton and it find only some minor leaks – the memory leaked was a couple of hundred bytes and the program continuously grows. When searching deeper, it seems like two functions is responsible for a large majority of the memory footprint:

std::string serialize()
{

 //Build basic message

 std::string result="";
        //std::cout << "result: " << result << "\n";
        result+=m_topic+d;
 //std::cout << "result: " << result << "\n";
 result+=m_message+d;
 //std::cout << "result: " << result << "\n";
 char buf[12];
 std::cout << m_severity << "\n";
 snprintf(buf, sizeof(buf), "%d", m_severity);
 //std::cout << "Buffer:" <<  buf << "\n";
 std::string temp(buf);
 result+=temp+d;
 //std::cout << "result: " << temp << "\n";

 int messagelength=strlen(result.c_str());
 snprintf(buf, sizeof(buf), "%d", messagelength);
 //std::cout << "Buffer:" <<  buf << "\n";
 std::string temp2(buf);
 temp2+=d;
 temp2+=result;
 //std::cout << "result: " << temp2 << "\n";
 return temp2;
}

and

std::string message::prettyPrint()
{
 struct tm *Sys_T= NULL;
 time_t Tval = 0;   
 Tval = time(NULL);
 Sys_T = localtime(&Tval);
 std::string date;
 char buf[10];
 sprintf(buf,"%d:%d:%d (%d/%d 2010)",Sys_T->tm_hour, Sys_T->tm_min, Sys_T->tm_sec, Sys_T->tm_mday, Sys_T->tm_mon);
 date+=std::string(buf);

 char sevbuf[10];
 sprintf(sevbuf,"%d",m_severity);

 delete Sys_T;
 std::string printed= "---------------------Message--------------------- \n";
 printed+= +"\n "+ date + ":  [[" +  getTopic() + "]]\n\n" +
 + " Message:" + m_message + "\n"
 + " Severity " + std::string(sevbuf) +" \n";
 //+ " Serialized " + serialize() + "\n";
 return printed;
}

As you can see this is merely stack allocated objects.

At the same time, the “Instrument” memory observer reports that the number of “active” allocated memory does not grow.

I am not so familiar with programming or these terms – my question is:

• Can my application leak memory that is not reported by memory leak searching application?
• Is RSS not reporting the “active” memory set but also the historical ones?

Answer 1

Even though your objects are merely stack allocated, the class implementations may allocate memory in the heap. For example, std::string will do this.

Allocating and deallocating memory in the heap can lead to fragmentation, which would explain the increased memory usage. See http://en.wikipedia.org/wiki/Malloc#Heap-based

Edit: Looking closer at your code, there are other problems — as the others have pointed out.