You can have more than one executor in some implementations (you know you do if you can keep more than one CPU busy), but in all the implementations you're certainly causing problems if you sync-block an executor for long periods of time, that's not what the system is for. By contrast, you want to open a thread/goroutine/Erlang process/Haskell spark/execution context in a threaded language and have it just bang away on numeric computation for a few days? Usually that's just fine, though if you've got a green-threading implementation, double-check first. Most green thread implementations seem to go through a period where that is not fine, but then eventually it is; Go for instance passed through that quite a few versions ago.
You can have more than one executor in some implementations (you know you do if you can keep more than one CPU busy), but in all the implementations you're certainly causing problems if you sync-block an executor for long periods of time, that's not what the system is for. By contrast, you want to open a thread/goroutine/Erlang process/Haskell spark/execution context in a threaded language and have it just bang away on numeric computation for a few days? Usually that's just fine, though if you've got a green-threading implementation, double-check first. Most green thread implementations seem to go through a period where that is not fine, but then eventually it is; Go for instance passed through that quite a few versions ago.