Erlang tips: How to check whether the target process has been started

Sometimes we need to determine whether the target process has been started. If the target process has not been started, an additional target will be started. Otherwise, skip

Generally, you can search the target process in the progress table.

In elrang, the Erlang: whereis function can be used.

Whereis (regname)-> PID () | Port () | undefined
Returns the PID or port identifier with the registered name regname. Returns undefined if the name is not registered.
Example:
> Whereis (db ).
<0.43.0>

Example:

Ensure_started (ARGs)->

Case Erlang: whereis (? Server)
Undefined->

{OK, PID} = gen_server: start_link ({local ,? Server },? Module, [ARGs], []),

PID.

PID when is_pid (PID)->

% Some trace here
PID

End.