If you start a service, it's just one process, right? So if it fails, all pending requests will fail, right?
What is the recommended way to contain a failure to a single request?
What is the recommended way to contain a failure to a single request?
If you search for "So we will create a module named ch3 with gen_server behaviour", you'll see the author's server code. His server code makes use of the gen_server behavior.
To answer your questions:
Yes. If the author's server process crashed, all pending requests would be lost. From what I can tell, gen_servers use the Erlang process mailbox to maintain a queue of (among other things) requests to be serviced. If a process dies, its mailbox is destroyed and its contents lost.
If I were concerned about my code's ability to survive a crash of one of its operations, I would either
* Wrap the operation in a try/catch block that only handled all of the error conditions that I was expecting to encounter.
* Execute the operation in a separate, monitored [0] process that sends a message back with the results of the operation. [1]
Each method has its place, but I would find myself using the child process method most of the time. Defensive coding is a really bad code smell in Erlang programs. Swallowing all exceptions is definitely a very defensive thing to do.
[0] Any process in an Erlang system can monitor any other process in the system and get a notification when the monitored process terminates.
[1] You can even tell your supervisor to start the process for you so that it knows about it and can terminate the child if the supervisor is asked to shutdown.