Adventures of a Software Engineer

Month: March 2015

  • Taking heap dump of java process on linux and windows

    Taking a heap dump from console when Java VisualVM and JMX is not available to us.
    We will use following tools

      • jmap
      • jps
      • ps

    Dumping heap requires two steps
    1) Obtaining target process id
    2) Dumping heap for given pid

    First we need to obtain the target process id we would like to dump, here I will show couple ways I like to use.

    ps aux | grep 'java'
-----
userx     29901  6.7 47.0 25418812 3848276 ?    Sl   Mar23  85:42 /opt/java/bin/java -Djava.util.logging.config.

    Here second column indicates our process id (pid)

    Second method that is quite useful to obtain pid for java processes

    uxserx@WS4:/opt/java/bin# ./jps -l
4281 sun.tools.jps.Jps
29901 org.apache.catalina.startup.Bootstrap

    As we see both methods returned us pid of 29901
    Npw to perform the dump we issue our second command

    userx@WS4:/opt/java/bin# ./jmap -dump:format=b,file=/tmp/heapdump-001.hprof 29901
Dumping heap to /tmp/heapdump-001.hprof ...

    At this point we have our heap dump that is ready to be analyzed, for my analysis I use two tools. Eclipse Memory Analyzer (MAT) and Java Visual VM

  • Accessing data of leptonica PIX data

    This is mainly as a reference

    
/**
 * Get Pixel value at given  point
 */
l_uint32 pixAtGet(PIX* pix, int_t x, int_t y)
{
    l_int32 wpl    = pixGetWpl(pix);
    l_uint32* data = pixGetData(pix);
    l_uint32* line = data + y * wpl;
    l_uint32 value = GET_DATA_BYTE(line, x);
    return value;
}

    To set a pixel value we can use this

    /**
 * Set Pixel value at given  point
 */
void pixAtSet(PIX* pix, int_t x, int_t y, byte_t value)
{
	l_int32 wpl     = pixGetWpl(pix);
	l_uint32* data  = pixGetData(pix);
	l_uint32* line  = data + y * wpl;
	SET_DATA_BYTE(line, x, value);
}

  • Tokenizing/splitting string in c++

    This method uses strtok to tokeninze our string given a specific delimeter, results of that are put into supplied vector. There are few other ways we can do this but this one is straight forward.

    #include 
#include 
#include 

#include 
#include 
#include 
#include 
#include 

using namespace std;

void split(vector& out, const string& in, const string& delim)
{
  char* lc = (char*) malloc(in.size());
  strcpy(lc, in.c_str());
  strtok(lc, delim.c_str());
  while (lc)
    {
      string s = lc;
      out.push_back(s);
      lc = strtok(NULL, delim.c_str());
    }
  free(lc);
}

int main(int argc, char* args[])
{
  string str = "apple,organge,cherry";
  vector o1;
  split(o1, str, ",");

  for (int i = 0; i < o1.size(); ++i)
  {
     cout << "token = " << o1[i] <

    Results
    

    Supplied string : apple,organge,cherry
    
Delemeter : ","
    
Output
    

      

    • apple
      • 

    • organge
      • 

    • cherry
      •