C functions with COMMIT/ROLLBACK?

Hi everyone,

Is is possible to add handlers so that a C function is fired when a transaction is committed or rolled back, for example (pseudo code):

BEGIN;
CALL my_function(1);
CALL my_function(2);
CALL my_function(3);
ROLLACK;

my_function()
Create "my_file.txt.tmp"
Write some information to it

commit_handle()
Rename "my_file.txt.tmp" to "my_file.txt"

rollback_handle()
Delete "my_file.txt"

OK, now is it possible to get postgres to call commit_handle() or rollback_handle() for COMMIT and ROLLBACK respectively? Is it even possible to carry context information (for C) throughout an entire transaction?

P.S. Yes, I understand how silly that example is and all the things practically wrong with it but its the concept of firing a C function when a transaction ends and whether it succeeded or not.