I have a gen_server module that logs data to a file when a client process sends it data. What happens when two client processes send data at the same time to this module? Will the file operations conflict with each other? The erlang documentation is frustratingly unclear here.
Every Erlang process maintains a message queue. The process will fetch a message and handle the messages one by one.
In your example, if two clients calls the gen_server
at the same time, these calls will become a message in the queue of gen_server
process, and the gen_server
will process these messages one by one. So no need to worry about a conflict.
But if one process has to handle too many messages from other processes, you'll need to think about the capacity of the process and optimize the design, or else it will become a bottleneck.
The gen_server
runs in a separate process from your client process so when you do a call
/cast
to it you are actually sending messages to the server process.
All messages are placed in a process' message queue and processes handle their message one-by-one. If a message arrives while a process is busy then it is placed in the message queue. So log messages arriving concurrently will never interfere with each other as they will be processed sequentially.
This is not a property of the gen_server
as such but a general property of all processes in erlang, which is why no mention of this is made in the gen_server documentation.
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