Module 2Module 2

Programming with ProcessesProgramming with Processes

ProcessesProcesses

•Process -- a program in execution–May share code segments–Typically do not share data, stack, heap

•OS data structures (file handles, coroutine, context block) kept in struct named User•One User struct per process

•Process -- a program in execution–May share code segments–Typically do not share data, stack, heap

•OS data structures (file handles, coroutine, context block) kept in struct named User•One User struct per process

LoginLogin• Authenticates via name/password• Name converted to number(s)

– User Id– Group Id : used for sharing

Macintosh-2:~ shawne$ ls -ltotal 48drwx------+ 89 shawne staff 3026 Mar 1 14:03 Desktopdrwx------+ 7 shawne staff 238 Feb 13 15:50 Documentsdrwx------+ 5 shawne staff 170 Feb 19 11:07 Downloads

• Authenticates via name/password• Name converted to number(s)

– User Id– Group Id : used for sharing

Macintosh-2:~ shawne$ ls -ltotal 48drwx------+ 89 shawne staff 3026 Mar 1 14:03 Desktopdrwx------+ 7 shawne staff 238 Feb 13 15:50 Documentsdrwx------+ 5 shawne staff 170 Feb 19 11:07 Downloads

User id group id

Process Creation and Destruction

Process Creation and Destruction

int execle(const char *filepath,const char *arg, ..., (char *)0, char *const envp[] );/* replaces caller's memory image with "program" */

void exit(int status);/* terminates execution; returns status to parent */

pid_t wait(int *stat_loc);pid_t waitpid(pid_t pid, int *stat_loc, int options);/* blocks caller until a child terminates.

pid_t fork(void);/* duplicates the memory image of the caller */

int execle(const char *filepath,const char *arg, ..., (char *)0, char *const envp[] );/* replaces caller's memory image with "program" */

void exit(int status);/* terminates execution; returns status to parent */

pid_t wait(int *stat_loc);pid_t waitpid(pid_t pid, int *stat_loc, int options);/* blocks caller until a child terminates.

pid_t fork(void);/* duplicates the memory image of the caller */

#include <stdio.h>#include <stdlib.h>#include <unistd.h>

int main() { int pid, out; char *envp[]={"ME=BOB",0}; pid=fork(); printf("I am %d\n",pid); if (pid!=0) { wait(&out); printf("child returned %d\n",out); execle("/bin/echo","dog","cat",0,envp); } exit(55);}

#include <stdio.h>#include <stdlib.h>#include <unistd.h>

int main() { int pid, out; char *envp[]={"ME=BOB",0}; pid=fork(); printf("I am %d\n",pid); if (pid!=0) { wait(&out); printf("child returned %d\n",out); execle("/bin/echo","dog","cat",0,envp); } exit(55);}

C program usesOS APIs to write

commands

Shell programs

Window programs

Browser

Browser programs

C program usesOS APIs to write

commands

Shell programs

Window programs

Browser

Browser programs

UNIX ShellUNIX Shell

Boot-up to CommandBoot-up to Command

Remote Executionssh user@hostname command

Remote Executionssh user@hostname command

• Automatic login is desirable– The scheme is based on public-key

cryptography, using cryptosystems where encryption and decryption are done using separate keys, and it is infeasible to derive the decryption key from the encryption key.

– The idea is that each user creates a public/private key pair for authentication purposes. The server knows the public key, and only the user knows the private key.

– Private key encrypts login info; public key decrypts

• Automatic login is desirable– The scheme is based on public-key

cryptography, using cryptosystems where encryption and decryption are done using separate keys, and it is infeasible to derive the decryption key from the encryption key.

– The idea is that each user creates a public/private key pair for authentication purposes. The server knows the public key, and only the user knows the private key.

– Private key encrypts login info; public key decrypts

Data ParallelismData Parallelism• Why: speed-up

• How (greatly simplified): – split work into independent similar pieces– execute pieces in parallel– collect results

• Simple example– Count number of identifiers in a set of files

• Why: speed-up

• How (greatly simplified): – split work into independent similar pieces– execute pieces in parallel– collect results

• Simple example– Count number of identifiers in a set of files

Practical Parallel and Concurrent Programming DRAFT: comments to msrpcpcp@microsoft.com

106/16/2010

Count ids in several files./test foo.txt moo.txt boo.txt

Count ids in several files./test foo.txt moo.txt boo.txt

#include <unistd.h>#include <stdio.h>#include <sys/wait.h>

int main(int argc, char *argv[]) { int count=0, i;for (i=1; i<argc; i++) { if (fork()) continue; 

execl("./cnt","./cnt",argv[i],0);} //forfor (i=1; i<argc; i++) {    int cnt;    wait(&cnt);    count+=WEXITSTATUS(cnt);}printf("count = %d¥n", count);exit(0); }

#include <unistd.h>#include <stdio.h>#include <sys/wait.h>

int main(int argc, char *argv[]) { int count=0, i;for (i=1; i<argc; i++) { if (fork()) continue; 

execl("./cnt","./cnt",argv[i],0);} //forfor (i=1; i<argc; i++) {    int cnt;    wait(&cnt);    count+=WEXITSTATUS(cnt);}printf("count = %d¥n", count);exit(0); }

Shell procedure to count ids

Shell procedure to count ids

declare -i x=0for i in $* ; do   x=x+`./cnt $i` ;   echo $x ;DoneCommand Line./foo.sh /Users/bobcook/Desktop/*.txtOutput31826053141

declare -i x=0for i in $* ; do   x=x+`./cnt $i` ;   echo $x ;DoneCommand Line./foo.sh /Users/bobcook/Desktop/*.txtOutput31826053141

Amdahl’s hypothesisAmdahl’s hypothesis• Assume that sorting takes 70% of the

execution time of a sequential program• You replace the sorting algorithm with

one that scales perfectly on multi-core hardware

• How many cores do you need to get a 4x speed-up of the program?

• Assume that sorting takes 70% of the execution time of a sequential program

• You replace the sorting algorithm with one that scales perfectly on multi-core hardware

• How many cores do you need to get a 4x speed-up of the program?

6/16/2010 Practical Parallel and Concurrent Programming DRAFT: comments to msrpcpcp@microsoft.com

14

6/16/2010 Practical Parallel and Concurrent Programming

DRAFT: comments to msrpcpcp@microsoft.com 15

Amdahl’s Formula

6/16/2010 Practical Parallel and Concurrent Programming

DRAFT: comments to msrpcpcp@microsoft.com 16

Speedup achieved with perfect scalingSpeedup achieved

with perfect scaling

Amdahl’s law limit, just 1.11x

Amdahl’s law limit, just 1.11x

f = 10%

6/16/2010 Practical Parallel and Concurrent Programming

DRAFT: comments to msrpcpcp@microsoft.com 17

Desired 4x speedup

Desired 4x speedup

Speedup achieved (perfect scaling on 70%)

Speedup achieved (perfect scaling on 70%)

Limit as c→∞ = 1/(1-f) = 3.33Limit as c→∞ = 1/(1-f) = 3.33

f = 70%

6/16/2010 Practical Parallel and Concurrent Programming

DRAFT: comments to msrpcpcp@microsoft.com 18

f = 98%

LessonLesson

• Speedup is limited by sequential code

• Even a small percentage of sequential code can greatly limit potential speedup

• Speedup is limited by sequential code

• Even a small percentage of sequential code can greatly limit potential speedup

6/16/2010 Practical Parallel and Concurrent Programming DRAFT: comments to msrpcpcp@microsoft.com

19

Reasons for IPC

Information sharing

Program speedup

Fault tolerance

Resource limitations per node

Heterogeneity

Modularity

Convenience

Privilege separation -- different levels of protection

Inter-Process Communication (IPC)

Inter-Process Communication (IPC)

PipesMessage queuesShared memoryShared filesSignalsSockets (TCP/IP protocols)Message passing (MPI, discussed later)Semaphores (discussed later)Remote variable access (discussed later)Remote procedure call (discussed later)Remote process invocation (ssh commands)

Common IPC APIsCommon IPC APIs

#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <string.h>

int main() { //pipe input to sort command  FILE *write;  char *str[]={"hi", "by", "so", "mo"};  int i;  write = popen("sort", "w");  if (write !=NULL) {    for (i=0; i<4; i++) fprintf(write, "%s\n", str[i]);    pclose(write);    exit(EXIT_SUCCESS);  }  exit(EXIT_FAILURE);}OUTPUT by hi mo so

Pipe Command Example(invoke commands from C

programs)

Pipe Command Example(invoke commands from C

programs)

#include <unistd.h>

int pipe(int fildes[2] /* out parameter*/);fildes[0] - read end of pipefildes[1] - write end of pipe

Be aware that write() can write less than you request and read() can read less. File handles are inherited by fork()/exec() processes.

Pipe System Call APIPipe System Call API

FIFO File Object System APIFIFO File Object System API#include <sys/types.h>#include <sys/stat.h>

int mkfifo(const char *path, mode_t mode);

Like a file, a FIFO can be opened for reading or writing or both intermittently.

Message Queue APIMessage Queue API

Message Queue -record oriented

Message Queue -record oriented

#include <fcntl.h> /* For O_* constants */#include <sys/stat.h> /* For mode constants */#include <mqueue.h>struct mq_attr { long mq_flags; /* Flags: 0|O_NONBLOCK */ long mq_maxmsg; /* Max. # of msgs on Q*/ long mq_msgsize; /* Max. msg size (bytes) */ long mq_curmsgs; /* # msgs currently in Q*/};mqd_t mq_open(const char name[], int oflag); //to open onlymqd_t mq_open(const char name[], int oflag, mode_t access_mode, struct mq_attr *attr);int mq_close(mqd_t mqdes);int mq_unlink(const char name[]);

int mq_send(mqd_t mqdes, const char msg_ptr[], size_t msg_len, unsigned msg_priority);ssize_t mq_receive(mqd_t mqdes, char msg_ptr[], size_t msg_len, unsigned *msg_priority);

Processing Multiple Files in ParallelOne thread per Chunk

Shared Memory Among Multiple Processes

//returns shmid for new segment of size bytesint      shmget(key_t key, size_t size, int mode_t);

//control ops such as stat, unlink, lock, unlockint      shmctl(int shmid, int cmd, struct shmid_ds *buf);

//attach segment to process at shmaddrvoid *shmat(int shmid, const void *shmaddr, int shmflag);

//detach segment at shmaddr from this processint     shmdt(const void *shmaddr);

Shared Memory API

Memory-Mapped Files forIncreased Efficiency

#include <sys/mman.h>

void *mmap(void *start_addr, size_t length, int protection, int flags, int filedescriptor, off_t offset);

int     munmap(void *start_addr, size_t length);

Memory-Mapped File API