Kiss!

• Write the "answer" as a directory name at a particular place in the file system.

  Say /usr/shared/appname/cache/xxxxxx/

• Applications reading the data simply glob the path /usr/shared/appname/cache/*.

  They get back a single name that is the answer to the question.

  If the readers need to be able to tell how fresh the answer is, they can stat the modified time.

  No locking involved.

• The "writing" script, uses the atomic nature of rename to update the directory name at the appropriate times.

  No locking involved.

If the answer is too big to fit into a directory name, then use a file with a well-known name.

• Readers just read the contents.
• The writer writes updates to a different name and then deletes the original and renames.

  This requires the readers to retry if their attempts to open or read fail.