google-perftools' heap profiler: http://google-perftools.googlecode.com/svn/trunk/doc/heapprofile.html

cpu_prof.rb

module CpuProf
  require 'ffi'
  extend FFI::Library
  ffi_lib FFI::CURRENT_PROCESS

  begin
    attach_function :start, :ProfilerStart, [:string], :void
    attach_function :stop, :ProfilerStop, [], :void
  rescue FFI::NotFoundError => e
    STDERR.puts "*** Are you sure you preloaded libprofiler?"
    STDERR.puts "*** {DYLD_INSERT_LIBRARIES,LD_PRELOAD}=/path/to/lib/libprofiler.so ruby file.rb"
    STDERR.puts e.inspect
    exit!(1)
  end
end

heap_prof.rb

# Simple memory profiler using google-perftools' tcmalloc.
#
# Usage:
#   HeapProf.start("myapp")
#   100.times{ "a"*1000 }
#   HeapProf.dump("checkpoint")
#   HeapProf.stop
#
# Reporting:
#   pprof `which ruby` myapp.0001.heap --gif > myapp.gif
#
# Advanced (memory growth between two checkpoints):
#   pprof `which ruby` --base=myapp.0001.heap myapp.0002.heap --gif > myapp.gif
#
module HeapProf
  require 'ffi'
  extend FFI::Library
  ffi_lib FFI::CURRENT_PROCESS

  begin
    attach_function :start, :HeapProfilerStart, [:string], :void
    attach_function :dump, :HeapProfilerDump, [:string], :void
    attach_function :stop, :HeapProfilerStop, [], :void
  rescue FFI::NotFoundError
    STDERR.puts "*** Are you sure you preloaded libtcmalloc?"
    STDERR.puts "*** {DYLD_INSERT_LIBRARIES,LD_PRELOAD}=/path/to/lib/libtcmalloc.so ruby file.rb"
    exit!(1)
  end
end