diff options
Diffstat (limited to 'railties')
| -rw-r--r-- | railties/guides/source/active_support_overview.textile | 20 |
1 files changed, 19 insertions, 1 deletions
diff --git a/railties/guides/source/active_support_overview.textile b/railties/guides/source/active_support_overview.textile index aea77c8d4e..93c189ddb6 100644 --- a/railties/guides/source/active_support_overview.textile +++ b/railties/guides/source/active_support_overview.textile @@ -789,7 +789,25 @@ h3. Extensions to +Pathname+ h3. Extensions to +File+ -... +h4. +atomic_write+ + +With the class method +File.atomic_write+ you can write to a file in a way that will prevent any reader from seeing half-written content. + +The name of the file is passed as an argument, and the method yields a file handle opened for writing. Once the block is done +atomic_write+ closes the file handle and completes its job. + +For example, Action Pack uses this method to write asset cache files like +all.css+: + +<ruby> +File.atomic_write(joined_asset_path) do |cache| + cache.write(join_asset_file_contents(asset_paths)) +end +</ruby> + +To accomplish this +atomic_write+ creates a temporary file. That's the file the code in the block actually writes to. On completion, the temporary file is renamed. If the target file exists +atomic_write+ overwrites it and keeps owners and permissions. + +WARNING. Note you can't append with +atomic_write+. + +The auxiliary file is written in a standard directory for temporary files, but you can pass a directory of your choice as second argument. h3. Extensions to +Exception+ |