more GC tuning

on ruby2.1 and later, do an incremental GC on every write
on older ruby, full GC every 100 writes

see #67

CHANGELOG.md

@@ -1,5 +1,10 @@
 # master 
 
+# Version 0.3.14
+
+* more GC tuning [felixbuenemann]
+* add `write.rb` example program [felixbuenemann]
+
 # Version 0.3.13
 
 * don't use generational GC options on old Rubys [John Cupitt]

examples/write.rb

@@ -0,0 +1,28 @@
+#!/usr/bin/env ruby
+
+require 'rubygems'
+require 'vips'
+
+repeat = 2000
+
+def rss
+    `ps -o rss= -p #{$$}`.chomp.to_i/1024
+end
+
+GC.start
+puts "RSS at startup with gems loaded: %d MB" % [rss]
+
+repeat.times do |i|
+    ARGV.each do |filename|
+        img = VIPS::Image.jpeg filename, :sequential => true
+
+        img = VIPS::JPEGWriter.new(img, quality: 50)
+        img.write('test.jpg')
+
+        print "\rIteration: %-8d RSS: %6d MB File: %-32s".freeze % [i+1, rss, filename]
+    end
+end
+puts
+
+GC.start
+puts "RSS at exit: %d MB" % [rss]

lib/vips/version.rb

@@ -1,3 +1,3 @@
 module VIPS
-  VERSION = "0.3.13"
+  VERSION = "0.3.14"
 end

lib/vips/writer.rb

@@ -6,29 +6,31 @@ def write(path)
 
     private
 
-    # write can fail due to no file descriptors 
+    # write can fail due to no file descriptors, memory can fill if large
+    # objects are not collected fairly soon
     #
     # we can't try a write and GC and retry on fail, since the write may take a
     # long time 
     #
     # GCing before every write would have a horrible effect on performance, so
     # as a compromise we GC every @@gc_interval writes
-
-    # ruby2.1 introduced a generational GC which can do a low-impact GC ... we
-    # behave differently for this
+    # 
+    # ruby2.1 introduced a generational GC which 
+    # is fast enough to be able to GC on every write
+
     @@generational_gc = RUBY_ENGINE == "ruby" && RUBY_VERSION.to_f >= 2.1
 
-    @@gc_interval = if @@generational_gc then 10 else 100 end
+    @@gc_interval = 100
     @@gc_countdown = @@gc_interval
 
     def write_gc(path)
-      @@gc_countdown -= 1
-      if @@gc_countdown < 0 
-        @@gc_countdown = @@gc_interval
-        if @@generational_gc 
-            GC.start full_mark: false, immediate_sweep: false
-        else
-            GC.start 
+      if @@generational_gc 
+        GC.start full_mark: false
+      else
+        @@gc_countdown -= 1
+        if @@gc_countdown < 0 
+          @@gc_countdown = @@gc_interval
+          GC.start 
         end
       end