From: "Sven C. Koehler" <schween@...>
Date: 2008-08-20T04:46:24+09:00
Subject: Hard question: Any ideas why this code leaks memory?

Hello,

could someone help me understand why this code leaks memory? (I am using
ruby 1.8.6 (2007-12-03 patchlevel 113) [x86_64-linux].)

def rss_leaks
  /^VmRSS:\s+(\d+)/m.match(File.open("/proc/#{$$}/status") {|f| 
      f.read })[1].to_i
end

| irb(main):002:0> 100000.times { rss_leaks }; rss_leaks
| => 11624
| irb(main):003:0> 100000.times { rss_leaks }; rss_leaks
| => 16836
| irb(main):004:0> 100000.times { rss_leaks }; rss_leaks
| => 22008
| irb(main):005:0> 100000.times { rss_leaks }; rss_leaks
| => 27248
| irb(main):006:0> 100000.times { rss_leaks }; rss_leaks
| => 32468

Calling GC.start inbetween does not help, but when we rewrote rss_leaks
this way the leaks disappeared:

def rss_no_leaks()
   d = File.open("/proc/#{$$}/status") {|f| f.read }
   /^VmRSS:\s+(\d+)/m.match(d)[1].to_i
end

| irb(main):002:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6568
| irb(main):003:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6568
| irb(main):004:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6588
| irb(main):005:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6592
| irb(main):006:0> 100000.times { rss_no_leaks }; rss_no_leaks
| => 6572

Any help to further understand what actually causes these leaks would be
very appreaciated!

Best wishes,

Sven