Issue #11626 has been reported by GC Yang.

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Bug #11626: fprintf in c extension keep adding memory usage
https://bugs.ruby-lang.org/issues/11626

* Author: GC Yang
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: 1.9.3p550
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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fprintf will keep adding memory usage without releasing it. 

I was doing it in rails console, not sure if it makes any different. The code like this:

VALUE leak (VALUE self, VALUE in) {
  char *str = StringValuePtr(in);
  char *pstr;
  pstr = malloc (10240);
  strcat(pstr,str);
  fprintf (stdout, pstr);
  self = rb_str_new_cstr(pstr);
  free (pstr);
  return self;
}

void Init_extension(){
  rb_define_global_function("leak", leak, 1);
}

100000000.times{leak("lots of garbage")}

without the fprintf line the memory usage is normal, adding that line just keep adding memory, kill the console process will release the memory. 

If I do 100000.times{Process.wait(fork{ stuff})}, memory also looks normal. Leaking somewhere???? 



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