Ch.03 Outline

1
Ch.03 Outline

• Process concept
• Definition
• Process states
• PCB
• Threads
• Process scheduling
• Queues
• Job, ready, device

2
Ch.03 Outline (cont)

• Process scheduling (cont)
• schedulers
• Job(long-term), CPU (short-term) swap
  (medium-term)
• Context switch
• Operations on processes
• Creation
• Termination

3
Ch.03 Outline (cont)

• Cooperating processes
• motivation
• Consumer/producer problem
• (shared memory)
• Interprocess communication
• Message-passing
• Naming
• Direct vs indirect

4
Ch.03 Outline (cont)

• Interprocess communication (cont)
• Synchronization
• Blocking vs nonblocking
• Buffering
• Zero
• Bounded
• Unbounded

5
Ch.03 Outline (cont)

• Comm in client/server systems
• sockets
• Remote procedure calls (RPC)
• Issues
• Remote method invocation (RMI)

6
PRESENTATION

• Process scheduling (?3.2)
• Queues
• Job, ready, device
• Process scheduling (cont)
• schedulers
• Job(long-term), CPU (short-term) swap
  (medium-term)
• Context switch

7
PRESENTATION

• Presentation (cont)
• Operation on Processes(?3.3)
• Creation
• Fork, execlp, wait
• Termination
• Exit, abort, kill
• PP. 83 92 in the text

8
processes

• Slide 4.2
• Compare program, process(job), task and thread in
  terms of size or work unit
• job (early term)
• Definition of above terms
• Need of a stack data section
• reentrant

9
Process states

• Slide 4.4
• Scheduling occurs when CPU is idle (timer
  interrupt, termination or I/O) or a process
  changes its state to ready (higher priority
  process)
• Interrupted programs (by I/O not timer) are
  handled by interrupt stack and re-scheduling is
  not involved,i.e., no state changes

10
PCB

• Slide 4.5
• PCB
• it is like a name or student id for a person
  and used for mgmt but it is not the actual being
  (as in file descriptor for files)

11
Exceptional conditions

• Made a mistake
• Slide 4.10 has a queue for wait for
  interrupt and I did not see that because of my
  prejudice
• Exceptions are interrupts, traps, faults and
  aborts.
• Executing process is suspended and control goes
  to the exceptions handler in the OS kernel.

12
Exceptional conditions

• 1. Interrupts
• asynchronous, signal from I/O devices external
  to CPU.
• timer interrupts
• put SP back in RQ and reschedule
• other interrupts
• put SP in current frame and adjust frame in
  interrupt stack for interrupt handler and process
  the interrupt.

13
Exceptional conditions

• 1. Interrupts (cont)
• continue I/O if more interrupts are expected
  (initiation, continuation termination). For
  termination, make any interrupt waiting process
  ready, if it exists.
• the remaining classes of exceptional
  conditions(trap, fault, abort) occur
  synchronously as a result of current instruction
  execution.

14
Exceptional conditions

• 2. Traps
• For I/O, a new system process different
  from caller is created and enqued to that device
  que (I/O que). Schedule device ques and ready
  queue. Enque the suspended process to WIF queue
  and it will later become ready again by an
  interrupt.

15
Exceptional conditions

• 2. Traps (cont)
• For non-I/O, a new process may not be
  necessary and works like a usual procedure
  call/return except that caller executes in user
  mode and system calls in supervisor mode.
• 3. Faults
• Correct the problem if possible, otherwise
  abort (e.g. divide error).

16
Exceptional conditions

• 3. Faults (cont)
• Error correction requires system calls and
  works like a trap afterwards (page fault)
• 4. Aborts
• hardware error, abort system call
• Terminate the process and reschedule.

17
schedulers

• Slide 4.11
• Job scheduler (long-term)
• Input spooling
• card reader (special handling in I/O)
• manual interrupt as in KB, mouse
• Degree of multiprogramming
• Job mix (CPU or I/O bound)
• Swapping (mid-term)

18
Process termination

• Slide 4.18
• Cascade
• Cascading termination

19
Process communication

• Process communication
• Cooperating processes must communicate and
  synchronize their activities with others (slide
  4.19)
• Shared memory (producer/consumer)
• IPC (without shared memory)
• direct indirect (slides 4.26-29)

20
Client/server comm

• Client/server communication
• Sockets concatenation of IPport
• Port number identifies specific services e.g.
  telnet23, ftp21,etc.
• RPC
• Built on top of IPC
• Stub on both sides

21
RPC

• RPC (cont)
• Parameter marshalling by stubs
• Issues
• External data representation (diff syss)
• comm failure (timestamps)
• binding of client and server ports
• fixed or matchmaker daemon

22
Word power

• Daemon, daimon a divinity or a
• manifestation of divine power in
• ancient Greek belief
• Paradigm an example serving as a
• model or pattern
• a set of all inflected forms of a word
• based on a single stem or root
• ex. Boy, boys, boys, boys

23
homework

• List and explain two major issues in RPC
  operation.
• Solve exercise 4.6.
• What is the main reason causing poor performance
  in message systems?
• What is meant by process migration between
  different queues?
• Solve problem 4.4.