1. Chapter 11: Distributed Processing Variations of subprogram control
Explicit call statements
Exception handlers
Subprograms must execute completely
Co-routines
Control must be transferred immediately
Scheduled subprograms
Single execution sequence
Parallel programming

2. Exceptions and exception handlers
Exception Handlers are subprograms that are not invoked by explicit calls
Special situations, called exceptions:
Error conditions
Unpredictable conditions
Tracing and monitoring

3. Exceptions and exception handlers
Exception handlers typically contain only:
A set of declarations of local variables
A sequence of executable statements
Exception Handlers can be
predefined in the language
programmer defined

4. Raising and catching an exception
Languages provide methods for raising (throwing) and testing for exceptions.
try {
statement1;
statement2; …
if badCondition throw ExceptionName; }
catch ExceptionName
{ ……….// do something for exception…….}

5. Implementation
.Operating system exceptions - raised directly by hardware interrupts.
.Programmer defined -
the translator inserts code to handle the exceptions.

6. Co-routines
Subprograms that can return control to the caller before completion of execution.
Resume B
Resume A
Coroutine A
Coroutine B

7. Implementation of co-routines
Similar to the simple call-return structure, the difference is in handling the CIP.
Each co-routine has IP location in its activation record,
used to provide the value for CIP on resuming the execution.

8. Scheduled subprograms
Subprograms scheduling techniques:
Execution after other subprograms – call B after A
Execution when a Boolean expression is true – call B when X=5
Execution on the basis of a simulated time scale - call B when time=25
Execution based on priority – call B with priority 7

9. Implementation of scheduling techniques
Scheduling is a run-time activity.
The process is controlled (usually) by a system-defined scheduler program that maintains a list of currently scheduled subprogram activations.