imitation hi-pri occam tool?

[Lawrence Dickson <tjoccam@xxxxxxxxxxxxx>]

All,
   I have a problem that has come up at work, and if anyone can point
me to a STANDARD library or toolset in the "Unix-Linux-C-driver" (not
C++) world, it would help us. It is like a high-priority occam process.

  begin -> code -> condition -> code -> condition ... -> code -> end

(the arrows may or may not mean structure pointer evaluation: a
chaining sequence is required). The conditions are asynchronous.
Working from the left, stuff is executed in "user" space until a false
condition (wait required) is found. From then on, conditions are tested
in asynchronous interrupts (for quick response) and code in "bottom
half" or immediate queue space (to avoid delays in other interrupt
response). Code can spawn its own sequence of "begin" commands, which
amounts to a PAR construct.
   So the asynchronous interrupt code loads the immediate queue, and
the immediate queue chains conditions onto the asynchronous interrupt.
Obviously we can set up the structures required to do this, but my
boss, Erik Peterson, is hoping somebody already invented this wheel.
   TIA,
   Larry Dickson