QMCS 360 Class Notes # 11	Dr. Rick Smith Quantitative Methods and Computer Science
Dr. Smith Home | Research | Classes | Blackboard | Cryptosmith | QMCS Home | UST A-Z | UST Home last update: Tuesday, October 18, 2005

Describe Quiz

Concurrency in our Favorite OSes (Sections 6.7-8-9-10)

Unix

Actually, System V, Release 4 (circa 1992)

IPC mechanisms

Pipes - we talked about these - a stream of data between processes

Named and unnamed pipes

Messages - more packet-like

Queued for the receiving process

Receiver can process them FIFO or by a sender-selected "type"

Shared Memory

All the obvious benefits and liabilities

Signals

Each signal is assigned a bit in the PCB - gets set when occurs

Process may establish a "signal handler" for each signal - it gets run when that signal occurs

Semaphores

An overdesigned service that provides every semaphore feature known to science, and a few never tried before

Linux

Includes SVR4 functions

Also...

Atomic operations

Establish a special "atomic" integer data type

Noninterruptable updates, also test-and-set

Requires that "atomic" operations are always used

Prevents accidental accesses by non-atomic operations

Can implement "real" shared variables

Can implement spinlocks

Bitmap updates

Implement noninterruptable bitmap update

Implement informal spinlocks on bitmap entries

True spinlocks

Various flavors depending on the "execution context"

Interrupts enabled, disabled, context saved, part of interrupt routine, etc.

Clearly for Kernel use only

Reader-Writer spinlocks - give many readers access to spinlock, but only one writer - it's more efficient that way

Semaphores

User-level = same as SVR4

Kernel-level are built-in to kernel and more efficient than user-level ones

Reader/writer semaphores, like the spinlocks

Barriers

Compiler-aware functions that prevent optimizations that reorder instructions.

Inserted in necessary places in device drivers, for example.

Solaris Thread Synchronization

Mutex Locks - some nonblocking

mutex-enter

mutex-exit

mutex-tryenter

Counting Semaphores - some nonblocking

sema-p = wait

sema-v = signal

sema-tryp = try it

Readers/Writer Lock = all potentially blocking

rw-enter

rw-exit

rw-downgrade

rw-tryupgrade

Condition Variable (like with monitors)

cv-wait

cv-signal

cv-broadcast

MS Windows

Object Oriented

Wait for object - includes a timeout

Synchronization objects - 4 explicit types to implement synchronization

Event - announces an event occurred

Mutex - acquire/release mutex in a thread

Semaphore - usual thing

Waitable timer - signals when done

Critical section objects

Similar to mutex objects, but only are visible to local threads

Faster, since no external context is required

Pluribus

Nonpreemptive

Spin locks

Deadlock and starvation detection