Chapter 3: Processes-Concepthscc.cs.nthu.edu.tw › ~sheujp › lecture_note › os08_CH03.pdf ·...
Transcript of Chapter 3: Processes-Concepthscc.cs.nthu.edu.tw › ~sheujp › lecture_note › os08_CH03.pdf ·...
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Chapter 3: ProcessesChapter 3: Processes--ConceptConcept
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3.2 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
ContentsContents
Process Concept
Process Scheduling
Operations on Processes
Cooperating Processes
Interprocess Communication
Communication in Client-Server Systems
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3.3 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process Concept (1)Process Concept (1)
Process (job): a program in execution (informally)
the unit of work in most systems
A system consists of a collection of processes (system processes and user processes) executing concurrently, with CPU multiplexed among them
A process is more than the program code (known as the text section). It also includes: (more formal definitionformal definition)
current activity (program counter, content of registers)
stack containing temporary data (e.g., parameters)
heap for dynamically memory allocation
data section containing global variables
a set of associated resources
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3.4 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process in MemoryProcess in Memory
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3.5 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process Concept (2)Process Concept (2)
program counterprogram counter: next instruction to be executed
A program is a passivepassive entity but a process is an activeactive entity
Two processes may be associated with the same program, they are considered as separate execution sequences
They have the same text section, but their data section will vary e.g., several users may running the copies of the mail/editor program
A process may spawnspawn many processes as it runs
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3.6 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process StateProcess State
As a process executes, it changes state
new: The process is being created
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 process
terminated: The process has finished execution
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3.7 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Diagram of Process StateDiagram of Process State
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3.8 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process Control Block (PCB)Process Control Block (PCB)
Information associated with each process
Process state
Program counter
CPU registers
CPU scheduling information
Memory-management information
Accounting information
I/O status information
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3.9 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process Control Block (PCB)Process Control Block (PCB)
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3.10 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
CPU Switch From Process to ProcessCPU Switch From Process to Process
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3.11 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process Scheduling QueuesProcess Scheduling Queues
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 among the various queues
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3.12 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Ready Queue And Various I/O Device Ready Queue And Various I/O Device QueuesQueues
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3.13 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Representation of Process Representation of Process SchedulingScheduling
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3.14 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
SchedulersSchedulers
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
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3.15 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
LongLong--term Scheduler (job term Scheduler (job Scheduler):Scheduler):
Selecting processes from the job pool and loads them into memory for execution
Execute less frequently (e.g., once several minutes)
Control the degree of multiprogrammingdegree of multiprogramming
Select a good process mixprocess mix of I/OI/O--boundboundprocessesprocesses and CPUCPU--bound processesbound processes
Some system, such as time-sharing system, do not have. Their multiprogramming degree are controlled by hardware limitation (e.g., # of terminals) or on the self-adjusting nature of users
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ShortShort--term scheduler (CPU term scheduler (CPU scheduler)scheduler)
Selecting one of the ready processes, and allocates the CPU to it.
Execute quite frequently (e.g., once per 100ms)
must be very fast e.g., if it takes 10 ms, then 10/(100+10) percent of CPU is wasted.
ready queue
I/O queue(s)I/O
CPUshort-termlong-term
end
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3.17 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Addition of Medium Term SchedulingAddition of Medium Term Scheduling
swap out: removing processes from memory to reduce the degree of multiprogramming.
swap in: reintroducing swap-out processes into memory
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3.18 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Context SwitchContext Switch
Context switch: saving the state of the old process and loading the saved state of the new process
This is a pure overheadoverhead
switch time (about 1~1000 ms) depends on
memory speed
number of registers
existence of special instructions
• e.g., a single instruction to save/load all registers
hardware support
• e.g., multiple sets of registers
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3.19 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Schedulers (Cont.)Schedulers (Cont.)
Short-term scheduler is invoked very frequently (milliseconds) (must be fast)
Long-term scheduler is invoked very infrequently (seconds, minutes) (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
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3.20 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process CreationProcess Creation
Parent process create 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 , the child ask new one from OS
Execution
Parent and children execute concurrently
Parent waits until children terminate
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3.21 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process Creation (Cont.)Process Creation (Cont.)
Address space
Child duplicate of parent , communication via sharing variables (it has the same program and data as the parent)
Child has a program loaded into it , communication via message passing
UNIX examples
fork system call creates new process
exec system call used after a fork to replace the process’s memory space with a new program
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3.22 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process CreationProcess Creation
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3.23 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
C Program Forking Separate ProcessC Program Forking Separate Process
int main(){Pid_t pid;
/* fork another process */pid = fork();if (pid < 0) { /* error occurred */
fprintf(stderr, "Fork Failed");exit(-1);
}else if (pid == 0) { /* child process */
execlp("/bin/ls", "ls", NULL);}else { /* parent process */
/* parent will wait for the child to complete */wait (NULL);printf ("Child Complete");exit(0);
}}
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3.24 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
A tree of processes on a typical A tree of processes on a typical SolarisSolaris
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3.25 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Process TerminationProcess Termination
Process executes last statement and asks the operating system to delete it (exit)
Output data from child to parent (via wait)
Process’s 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
If parent is exiting
Some operating system do not allow child to continue if its parent terminates
–All children terminated - cascading termination
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3.26 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Cooperating ProcessesCooperating Processes
Independent process cannot affect or be affected by the execution of another process
Cooperating process can affect or be affected by the execution of another process
Advantages of process cooperation
Information sharing ( e.g. a shared file)
Computation speed-up (e.g. parallel processing)
Modularity
Convenience (e.g., A user can performs several tasks at one time (editing, printing, compiling))
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3.27 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
ProducerProducer--Consumer ProblemConsumer Problem
Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process
unboundedunbounded--bufferbuffer places no practical limit on the size of the buffer
producer: no wait
consumer: wait when buffer is empty
boundedbounded--bufferbuffer assumes that there is a fixed buffer size
producer: wait when buffer is full
consumer: wait when buffer is empty
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3.28 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
BoundedBounded--Buffer Buffer –– SharedShared--Memory Memory SolutionSolution
Shared data
#define BUFFER_SIZE 10
Typedef struct {
. . .
} item;
item buffer[BUFFER_SIZE];
int in = 0;
int out = 0;
Solution is correct, but can only use BUFFER_SIZE-1 elements
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3.29 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
BoundedBounded--Buffer Buffer –– Insert() MethodInsert() Method
while (true) {/* Produce an item */
while (((in = (in + 1) % BUFFER SIZE count) == out)
; /* do nothing -- no free buffers */
buffer[in] = item;
in = (in + 1) % BUFFER SIZE;
{
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3.30 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Bounded Buffer Bounded Buffer –– Remove() MethodRemove() Method
while (true) {
while (in == out)
; // do nothing -- nothing to consume
// remove an item from the buffer
item = buffer[out];
out = (out + 1) % BUFFER SIZE;
return item;
{
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3.31 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
MessageMessage--Passing SystemsPassing Systems
Mechanism for processes to communicate and to synchronize their actions
Message system – processes communicate with each other without resorting to shared variables
IPC facility provides 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) such as channel or socket
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3.32 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Implementation QuestionsImplementation Questions
How are links established?
Can a link be associated with more than two processes?
How many links can there be between every pair of communicating processes?
What is the capacity of a link?
Is the size of a message that the link can accommodate fixed or variable?
Is a link unidirectional or bi-directional?
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3.33 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Logical LinksLogical Links
Several methods for logically implementing a link and the send/receive operations:
Direct or indirect communication
Symmetric or asymmetric communication
Automatic or explicit buffering
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3.34 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Direct CommunicationDirect Communication
Processes must name each other explicitly:
send (P, message) – send a message to process P
receive(Q, message) – receive a message from process Q
Properties of communication link
Links are established automatically
A link is associated with exactly one pair of communicating processes
Between each pair there exists exactly one link
The link may be unidirectional, but is usually bi-directional
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3.35 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Indirect CommunicationIndirect Communication
Messages are directed and received from mailboxes (also referred to as ports)
Each mailbox has a unique id
Processes can communicate only if they share a mailbox
Properties of communication link
Link established only if processes share a common mailbox
A link may be associated with many processes
Each pair of processes may share several communication links
Link may be unidirectional or bi-directional
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3.36 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Indirect CommunicationIndirect Communication
Operations
create a new mailbox
send and receive messages through mailbox
destroy a mailbox
Primitives are defined as:
send(A, message) – send a message to mailbox A
receive(A, message) – receive a message from mailbox A
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3.37 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Indirect CommunicationIndirect Communication
Mailbox sharing
P1, P2, and P3 share mailbox A
P1, sends; P2 and P3 receive
Who gets the message?
The answer depends on which of the following methods we choose
Allow a link to be associated with at most two processes
Allow only one process at a time to execute a receive operation
Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was.
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3.38 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
SynchronizationSynchronization
Message passing may be either blocking or non-blocking
Blocking is considered synchronous
Blocking send has the sender block until the message is received
Blocking receive has the receiver block until a message is available
Non-blocking is considered asynchronous
Non-blocking send has the sender send the message and continue
Non-blocking receive has the receiver receive a valid message or null
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3.39 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
BufferingBuffering
Queue of messages attached to the link; implemented in one of three ways
Zero capacity – 0 messagesSender must wait for receiver (rendezvous)
Bounded capacity – finite length of nmessagesSender must wait if link full
Unbounded capacity – infinite length Sender never waits
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3.40 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
ClientClient--Server CommunicationServer Communication
Sockets
Remote Procedure Calls
Remote Method Invocation (Java)
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3.41 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
SocketsSockets
A socket is defined as an endpoint for communication
Concatenation of IP address and port
The socket 161.25.19.8:1625 refers to port 1625 on host 161.25.19.8
Communication consists between a pair of sockets
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3.42 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Socket CommunicationSocket Communication
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3.43 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Remote Procedure CallsRemote Procedure Calls
Remote procedure call (RPC) abstracts procedure calls between processes on networked systems.
Stubs – client-side routine for the actual procedure on the server.
The client-side stub locates the server and marshals the parameters.
The server-side stub receives this message, unpacks the marshalled parameters, and performs the procedure on the server.
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3.44 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Execution of RPCExecution of RPC
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3.45 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Remote Method InvocationRemote Method Invocation
Remote Method Invocation (RMI) is a Java mechanism similar to RPCs.
RMI allows a Java program on one machine to invoke a method on a remote object.
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3.46 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Marshalling ParametersMarshalling Parameters
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3.47 Silberschatz, Galvin and Gagne ©2005Operating System Concepts
Home worksHome works
3.2, 3.3, 3.5, 3.6
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End of Chapter 3End of Chapter 3