Add File.atomic_write to prevent users from seeing half written files. Useful for situations like Page Caching and the like. [Koz]

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@6262 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

1 files changed, 21 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/file.rb b/activesupport/lib/active_support/core_ext/file.rb
new file mode 100644
index 0000000000..cd43be37e3
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/file.rb
@@ -0,0 +1,21 @@
+require 'tempfile'
+
+# Write to a file atomically.  Useful for situations where you don't
+# want other processes or threads to see half-written files.
+#
+#  File.atomic_write("important.file") do |file|
+#    file.write("hello")
+#  end
+#
+# If your temp directory is not on the same filesystem as the file you're 
+# trying to write, you can provide a different temporary directory.
+# 
+# File.atomic_write("/data/something.imporant", "/data/tmp") do |f|
+#   file.write("hello")
+# end
+def File.atomic_write(file_name, temp_dir = Dir.tmpdir)
+  temp_file = Tempfile.new(File.basename(file_name), temp_dir)
+  yield temp_file
+  temp_file.close
+  File.rename(temp_file.path, file_name)
+end
\ No newline at end of file