5.) INTERPROCESS COMMUNICATION

>For communication and synchronization
–Shared memory
–OS provided IPC
>Message system
–no need for shared variable
– two operations
•send(message) – message size fixed or variable
•receive(message)
>If P and Q wish to communicate, they need to
–establish a communication link between them
–exchange messages via send/receive
>Implementation of communication link
–physical (e.g., shared memory, hardware bus)
–logical (e.g., logical properties)

4.) COOPERATING PROCESSES

>Advantages of process cooperation
–Information sharing
–Computation speed-up
–Modularity
–Convenience
>Independent process cannot affect/be affected by the execution of another process, cooperating ones can
>Issues
–Communication
–Avoid processes getting into each other’s way
–Ensure proper sequencing when there are dependencies
>Common paradigm: producer-consumer
–unbounded-buffer - no practical limit on the size of the buffer
–bounded-buffer - assumes fixed buffer size

3.) OPERATION PROCESS

A.) PROCESS ON CREATION
Parent process creates children processes, which, in turn create other processes, forming a tree of processes.

Resource sharing:

>Parent and children share all resources.
>Children share subset of parent’s resources.
>Parent and child share no resources.

Execution:

>Parent and children execute concurrently.
>Parent waits until children terminate.

B.) PROCESS TERMINATION

>Process executes last statement and asks the operating system to delete it (exit).
>Output data from child to parent (via wait).
>Process’ resources are deallocated by operating system.
>Parent may terminate execution of children processes (abort).
>Child has exceeded allocated resources.
>Task assigned to child is no longer required.
>Parent is exiting.
>Operating system does not allow child to continue if its parent terminates.
>Cascading termination.
>In Unix, if parent exits children are assigned init as parent

2.) PROCESS SHEDULING

A.) SCHEDULING QUEUSE

>Job queue – set of all processes in the system.
>Ready queue – set of all processes residing in main memory, ready and waiting to >Execute.Device queues – set of processes waiting for an I/O device.
>Processes migrate between the various queues.

B.) SCHEDULERS

>Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue.
>Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU.

>Short-term scheduler is invoked very frequently (milliseconds) fi (must be fast).
>Long-term scheduler is invoked very infrequently (seconds, minutes) fi (may be slow).
>The long-term scheduler controls the degree of multiprogramming.
>Processes can be described as either:
>I/O-bound process – spends more time doing I/O than computations, many short CPU bursts.
>CPU-bound process – spends more time doing computations; few very long CPU bursts.


C.) CONTEXT SWITCH

>When CPU switches to another process, the system must save the state of the old process and load the saved state for the new process.
>Context-switch time is overhead; the system does no useful work while switching.
>Time dependent on hardware support.

1.) THE CONCEPTS OF PROCESS

A.) PROCESS STATE

-As a process executes, it changes state
new: The process is being created.F running: Instructions are being executed.
waiting: The process is waiting for some event to occur.
ready: The process is waiting to be assigned to a processor
terminated: The process has finished execution.

B.) PROCESS CONTROL BLACK

-Information associated with each process.
>Process ID
>Process state
>Program countern CPU registers
>CPU scheduling information
>Memory-management information
>Accounting information
>I/O status information

C.) THREADS

-Each process provides the resources needed to execute a program. A process has a virtual address space, executable code, open handles to system objects, a security context, a unique process identifier, environment variables, a priority class, minimum and maximum working set sizes, and at least one thread of execution. Each process is started with a single thread, often called the primary thread, but can create additional threads from any of its threads.

QUIZ NUMBER 3

1.) WHAT ARE THE MAJOR ACTIVITIES OF THE O.S WITH REGARDS TO PROCESS MANAGEMENT.

• Process creation and deletion
• Process suspension and resumption
• Provision of management for:
• Process synchornization
• Process communication
• Deadlack handling

2.) WHAT ARE THE MAJOR ACTIVITIES OF THE O.S WITH REGARDS TO MEMORY MANAGEMENT.

• Keep track of w/ parts of memory are curently being used and by whom.
• Decide w/c porcess to load when memory space becomes avalable.
• Allocate and dellocate memory space as needed.

3.) WHAT ARE THE MAJOR ACTIVITIES OF THE O.S WITH REGARDS TO SECONDARY-STORAGE MANAGEMENT.

• Free space management.
• Storage allocation.
• Disk scheduling.

4.) WHAT ARE THE MAJOR ACTIVITIES OF THE O.S WITH REGARDS TO FILE MANAGEMENT.

• File creation and deletion.
• Directory creation and deletion.
• Support of primitives for manipulating files and directories.
• Mapping files onto secondary storage.
• File backup on stable (volatile) storage media.

5.) WHAT IS THE PURPOSE OF THE COMMAND INTERPRETER

• Serves as the interface between the user and the operating system.
• User friendly, mouse based windows environment in the macintosh and in microsoft windows.
• Many command are given to the operating system by control statement with deals.
• Program that read and interpreters control statements is called variously.

SYSTEM BOOT

Operating system must be made available to hardware so hardware can start it

Small piece of code – bootstrap loader, locates the kernel, loads it into memory, and starts it
Sometimes two-step process where boot block at fixed location loads bootstrap loader
When power initialized on system, execution starts at a fixed memory location
Firmware used to hold initial boot code