1. Advances in Language Design
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Advances in Language Design
Lecture 18:
Dolores Zage

2. Topics Variations on Subprogram Control Parallel Programming
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Topics
Variations on Subprogram Control
Parallel Programming
Formal Properties of Languages
Language Semantics
Hardware Developments
Software Architecture

3. Where do advances come from?
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Where do advances come from?
Formal models of the programming process
experience->theory-> evaluation->
experience - programs have bugs, programming is hard
theory -> structured programming, BNF grammars, data abstractions
evaluation -> build languages using these concepts
These have lead to further improvements
object-oriented classes, SLR(1) and LALR(1) parsing techniques

4. Von Neumann Architecture
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Von Neumann Architecture
Computer consists
relatively large memory
a much faster but smaller control memory
CPU
All present languages implement these features

5. Changes in hardware and software architecture
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Changes in hardware and software architecture
Machines increase by a factor of 2 every 3 years
same basic problem remains -> control memory and CPU are always about an order of magnitude faster than the larger main memory
a computer spends much time simply waiting

6. Waiting Problem Solutions
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Waiting Problem Solutions
Software that allows for more efficient use of the hardware by concurrency
This permits the hardware to execute more efficiently by executing another program when one program is blocked waiting for data.
However, programmers are poor in rewriting applications to handle concurrency

7. Waiting Problem Solutions
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Waiting Problem Solutions
Another solution is develop more effective hardware
More cache
however the nature of computing of changing -> client/server

8. Variations on Subprogram Control
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Variations on Subprogram Control
Four assumptions on our usual activation record
explicit call statements are required
subprograms must execute completely at each call
immediate transfer of control at the point of call
single execution sequence

9. Exception and Exception Handlers
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Exception and Exception Handlers
Error conditions
conditions detected by the virtual computer
conditions generated by the semantics of the programming language
unpredictable conditions
tracing and monitoring

10. 4/20/2017
Coroutines
Drop the assumption to allow subprograms to return to their calling program before completion of execution.
Two subprograms swapping control back and forth as each executes
now used in simulation languages

11. Scheduled Subprograms
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Scheduled Subprograms
Relax the concept that execution of a subprogram should always be initiated immediately upon its call
one way to think of a call is it is to be scheduled for execution immediately
can be thought of exception
again used for discrete time simulation
note no main, just a scheduler

12. Nonsequential Execution
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Nonsequential Execution
Take away the assumption of single execution sequence
Parallel programming
Concurrent programming

13. Parallel Programming Multiprocessor system -> several CPUs
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Parallel Programming
Multiprocessor system -> several CPUs
Distributed or Parallel computer system has several computers each with its own memory and CPU connected with communication links into a network
multiprogramming and time sharing
major block - lack of support in PLs
for the most part, languages use additional OS calls

14. Parallel Programming Languages
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Parallel Programming Languages
Add complexity since several processors may be accessing the same data simultaneously
need 4 concepts
Variable definitions - mutable or definitional
Parallel composition - a statement to define threads
program structure - transformational or reactive
communication - shared memory or messages

15. Commands of Concurrency
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Commands of Concurrency
Construct to allow for parallel - the and
statement 1 and statement 2 and …
the statement beyond the and does not execute until all the parallel statements finish
guarded statements - nondeterministic execution
tasks - dependent
semaphores ...

16. Formal Properties of Programming Languages
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Formal Properties of Programming Languages
Chomsky Hierarchy
Undecidability
Is there a limit to what we can compute with a computer?
Instead of writing a C program, can you write another program that reads a description of the C program (its source file) and determines whether it would halt

17. Programming Verification
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Programming Verification
About the correctness and reliability
languages are being designed with features that enhance these attributes
assert in C++

18. Hardware Developments
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Hardware Developments
Improve the performance of a single CPU
develop alternative architectures

19. 4/20/2017
Processor Design
CISC - making instructions more powerful, fewer instructions, less movement of data
RISC

20. 4/20/2017
System Design
Single bus
crossbar switch
Omega network

21. Software Architecture
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Software Architecture
Persistent or transient data
read in persistent data into transient data within the program and then rewrite the transient data back into the persistent storage
this type of model is inefficient for some systems
reservation system

22. Transaction System Program executing continually
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Transaction System
Program executing continually
reservations occur at any time
just keep the data in transient
problem of system going down and losing the transient updates
solve this by a persistent programming language - no distinction between transient and persistent data

23. Networks and Client/Server Computing
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Networks and Client/Server Computing
Major impact on programming language design is the lack of a global data store for the program.
Both client and server only have limited access to the total information content of the program