Forces Ruby GC to compact the tcmalloc heap after garbage collecting

heap_compactor_ext.c

#include <ruby.h>
#include <stdlib.h>
#include <stdio.h>
#include <node.h>
#include <dlfcn.h>

void (*ReleaseFreeMemory)(void);

#ifdef RUBY_GC_EVENT_ALL
// requires https://github.com/tmm1/brew2deb/blob/master/packages/ruby/patches/gc-hooks.patch                                                                                                  
static void gc_hook(rb_gc_event_t gc_event, VALUE obj)
{
  switch(gc_event)
  {
    case RUBY_GC_EVENT_END:
      ReleaseFreeMemory();
      break;
  }
}
#endif

void Init_heap_compactor_ext()
{
#ifndef RUBY_GC_EVENT_ALL
  rb_raise(rb_eNotImpError, "rb_gc_add_event_hook() is not available in this ruby build");
#else
  ReleaseFreeMemory = dlsym(RTLD_DEFAULT, "MallocExtension_ReleaseFreeMemory");
  if (ReleaseFreeMemory == NULL)
    rb_raise(rb_eNotImpError, "tcmalloc is not linked in this ruby build");

  rb_gc_add_event_hook(gc_hook, RUBY_GC_EVENT_END);
#endif
}