There is no way to contact an unknown thread that may or may not be running. This means that any thread you wish to speak to needs
to be registered somehow in some list and have a means of "listening" to you, which in turn means SQLite (or indeed any other RDBMS)
cannot simply notify one or more other applications of something.
You will need to register some function with SQLite which you can call in a trigger (as Peter mentioned), but this function cannot
be attached in a different thread, i.e. you cannot have the function call the registered code from one or more OTHER
threads/applications than the one making the database connection, so you will need to make your own code in which, if the function
gets called, it contains a mechanism for communicating it to another instance or instances of itself, or indeed any other
apllication thread running in the OS which it somehow knows about and knows how to contact.
Another option is to have a continuous interrogation of some data table which contains possible messages that one application may
set and another may check until there is something to read, then read it and act accordingly. The caveat here is that one thread's
DB connection may not flush cached values for some time and it is IO intensive, depending on how fast polling you are doing and how
deterministic you need it to be. This sort of communication (if it can be called that) is ok if you have a slow non-deterministic
one-way notification need.
Personally, I prefer using a named pipe or socket connection on a local machine/device to an application which serves the changed
data. This is the purpose pipes/sockets exist for (as opposed to a file system), and it makes process visibility and debugging much
easier. (Not to mention the enormous ease with which it can later be scaled up to a multi-tiered networked / internet system). The
con here is that the serving application must be alive and running all the time for anyone else to know the current data state,
although a last-known-state DB table can be pressed into service here should this be a real problem.
RDBMSes should never be in charge of communications.
Have a great day!
PS: On Windows systems specifically you can also use the DDE service for inter-application communications, it's a cheap and nasty
solution, not my favourite, but sometimes cheap and nasty is what is needed. Sockets work cross-platform mostly and does not require
much of an application change if you do go multi-platform, just the socket layer itself adjusts.
On 2013/07/22 07:32, techi eth wrote:
I want to create a trigger on INSERT & in trigger logic I want to notify
other running executable in system.
Can I do this using trigger operation?
Example:
Create table ();
CREATE TABLE test (
ID INT PRIMARY KEY NOT NULL,
NAME TEXT NOT NULL,
);
CREATE TRIGGER Event_test1 AFTER INSERT
ON test
BEGIN
<Notify to other process either by registered callback OR signal>
END;
Cheers
Techi
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