Procesy Operan systmy 2009 Process in Memory Operan

Procesy Operačné systémy © 2009

Process in Memory Operačné systémy 3. 2 © 2009

Diagram of Process State Operačné systémy 3. 3 © 2009

Process Control Block (PCB) Operačné systémy 3. 4 © 2009

CPU Switch From Process to Process Operačné systémy 3. 5 © 2009

Ready Queue And Various I/O Device Queues Operačné systémy 3. 6 © 2009

Representation of Process Scheduling Operačné systémy 3. 7 © 2009

Addition of Medium Term Scheduling Operačné systémy 3. 8 © 2009

Process Creation Operačné systémy 3. 9 © 2009

C 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); } } Operačné systémy 3. 10 © 2009

A tree of processes on a typical Solaris Operačné systémy 3. 11 © 2009

Interprocess Communication n Processes within a system may be independent or cooperating n Cooperating process can affect or be affected by other processes, including sharing data n Reasons for cooperating processes: l Information sharing l Computation speedup l Modularity l Convenience n Cooperating processes need interprocess communication (IPC) n Two models of IPC l Shared memory l Message passing Operačné systémy 3. 12 © 2009

Communications Models Operačné systémy 3. 13 © 2009

Cooperating Processes n Independent process cannot affect or be affected by the execution of another process n Cooperating process can affect or be affected by the execution of another process n Advantages of process cooperation l Information sharing l Computation speed-up l Modularity l Convenience Operačné systémy 3. 14 © 2009

Producer-Consumer Problem n Paradigm for cooperating processes, producer process produces information that is consumed by a consumer process l unbounded-buffer places no practical limit on the size of the buffer l bounded-buffer assumes that there is a fixed buffer size Operačné systémy 3. 15 © 2009

Bounded-Buffer – Shared-Memory Solution n Shared data #define BUFFER_SIZE 10 typedef struct {. . . } item; item buffer[BUFFER_SIZE]; int in = 0; int out = 0; n Solution is correct, but can only use BUFFER_SIZE-1 elements Operačné systémy 3. 16 © 2009

Bounded-Buffer – Producer 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; } Operačné systémy 3. 17 © 2009

Bounded Buffer – Consumer 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; } Operačné systémy 3. 18 © 2009

Interprocess Communication – Message Passing n Mechanism for processes to communicate and to synchronize their actions n Message system – processes communicate with each other without resorting to shared variables n IPC facility provides two operations: l send(message) – message size fixed or variable l receive(message) n If P and Q wish to communicate, they need to: l establish a communication link between them l exchange messages via send/receive n Implementation of communication link physical (e. g. , shared memory, hardware bus) l logical (e. g. , logical properties) l Operačné systémy 3. 19 © 2009

Implementation Questions n How are links established? n Can a link be associated with more than two processes? n How many links can there be between every pair of communicating processes? n What is the capacity of a link? n Is the size of a message that the link can accommodate fixed or variable? n Is a link unidirectional or bi-directional? Operačné systémy 3. 20 © 2009

Direct Communication n Processes must name each other explicitly: l send (P, message) – send a message to process P l receive(Q, message) – receive a message from process Q n Properties of communication link l Links are established automatically l A link is associated with exactly one pair of communicating processes l Between each pair there exists exactly one link l The link may be unidirectional, but is usually bi-directional Operačné systémy 3. 21 © 2009

Indirect Communication n Messages are directed and received from mailboxes (also referred to as ports) l Each mailbox has a unique id l Processes can communicate only if they share a mailbox n Properties of communication link l Link established only if processes share a common mailbox l A link may be associated with many processes l Each pair of processes may share several communication links l Link may be unidirectional or bi-directional Operačné systémy 3. 22 © 2009

Indirect Communication n Operations l create a new mailbox l send and receive messages through mailbox l destroy a mailbox n Primitives are defined as: send(A, message) – send a message to mailbox A receive(A, message) – receive a message from mailbox A Operačné systémy 3. 23 © 2009

Indirect Communication n Mailbox sharing l P 1, P 2, and P 3 share mailbox A l P 1, sends; P 2 and P 3 receive l Who gets the message? n Solutions l Allow a link to be associated with at most two processes l Allow only one process at a time to execute a receive operation l Allow the system to select arbitrarily the receiver. Sender is notified who the receiver was. Operačné systémy 3. 24 © 2009

Synchronization n Message passing may be either blocking or non-blocking n Blocking is considered synchronous n l Blocking send has the sender block until the message is received l Blocking receive has the receiver block until a message is available Non-blocking is considered asynchronous l Non-blocking send has the sender send the message and continue l Non-blocking receive has the receiver receive a valid message or null Operačné systémy 3. 25 © 2009

Buffering n Queue of messages attached to the link; implemented in one of three ways 1. Zero capacity – 0 messages Sender must wait for receiver (rendezvous) 2. Bounded capacity – finite length of n messages Sender must wait if link full 3. Unbounded capacity – infinite length Sender never waits Operačné systémy 3. 26 © 2009

Examples of IPC Systems - POSIX n POSIX Shared Memory l Process first creates shared memory segment id = shmget(IPC PRIVATE, size, S IRUSR | S IWUSR); l Process wanting access to that shared memory must attach to it shared memory = (char *) shmat(id, NULL, 0); l Now the process could write to the shared memory sprintf(shared memory, "Writing to shared memory"); l When done a process can detach the shared memory from its address space shmdt(shared memory); Operačné systémy 3. 27 © 2009

Local Procedure Calls in Windows XP Operačné systémy 3. 28 © 2009

Communications in Client-Server Systems n Sockets n Remote Procedure Calls n Pipes n Remote Method Invocation (Java) Operačné systémy 3. 29 © 2009

Sockets n A socket is defined as an endpoint for communication n Concatenation of IP address and port n The socket 161. 25. 19. 8: 1625 refers to port 1625 on host 161. 25. 19. 8 n Communication consists between a pair of sockets Operačné systémy 3. 30 © 2009

Socket Communication Operačné systémy 3. 31 © 2009

Remote Procedure Calls n Remote procedure call (RPC) abstracts procedure calls between processes on networked systems n Stubs – client-side proxy for the actual procedure on the server n The client-side stub locates the server and marshalls the parameters n The server-side stub receives this message, unpacks the marshalled parameters, and peforms the procedure on the server Operačné systémy 3. 32 © 2009

Execution of RPC Operačné systémy 3. 33 © 2009