A simple library to manage resources which can be upgraded gracefully. This blog written in Chinese shows the usage of this library : http://blog.codeg.cn/2016/01/27/double-buffering/

During the continuous running period of a network server, there are some resources need to be updated on real-time. How to do an elegant resource upgrading? Here we propose a method to solve this problem which is called double-buffering technology. Double-buffering is a term that is well known throughout the graphics industry.

When double buffering is enabled, all resource upgrading operations are first initialized to a buffer handler instead of the handler which is being used by the process. After all initializing operations are completed, the buffer handler is swapped directly to the old one associated with it.

There is a simple example located in the example directory. The example provides a simple querying service which require two parameters: id and query. id is used as an identity of the client. query is used as the entity the querying. The service logic uses the query as a key to query a backend database and return the result. Avoiding vicious client to do request we provide an black-id-list which holds all the black ids.

Using the following steps to run this example:

$ git clone https://github.com/zieckey/dbuf
$ cd dbuf/example
$ go build
$ ./example ./black_id.txt

And in another console, we can do some requests:

$ curl "http://localhost:8091/q?id=123&query=jane"
hello, 123
$ curl "http://localhost:8091/q?id=475e5a499587a52ea14a23031ecce7c9&query=jane"
ERROR

id=123 is OK. But id=475e5a499587a52ea14a23031ecce7c9 is rejected.

Then we added 123 to the black-id-list. Now we have updated the black-id-list file and need it to be loaded into the service process. The simplest way is to stop the process and then start the process again. But during the continuous running period of a network server, this method will lose some requests during the stop-and-start period. It is very harmful to the client users.

So we use the double-buffering technology provided by this library. What we need to do is only to send a administration request to have it enabled. Like this:

$ curl "http://localhost:8091/admin/reload?name=black_id&path=./black_id.txt"
OK
$ curl "http://localhost:8091/q?id=123&query=jane"
ERROR

id=123 is rejected now. It works. Simple reload the dict file successfully.