Userland summaryUserland summary

Nezer J. ZaidenbergNezer J. Zaidenberg

Today’s topicsToday’s topics

• What have we learned - USERLAND summary• Revisited topics

• execXXX functions• POSIX cond• Daemons

• Sync methods we learned• EX 2 Pseudo code

• What have we learned - USERLAND summary• Revisited topics

• execXXX functions• POSIX cond• Daemons

• Sync methods we learned• EX 2 Pseudo code

Topics we covered - Processes

Topics we covered - Processes

• We learned how to create process (fork(2)) execute a run time (execXXX(2))

• How to wait(2) and waitpid(2) for process • We tried 2 methods of Inter process communications IPC

(network and UNIX domain sockets) - THERE ARE MANY MORE

• We understand process environment - File descriptor table, environment (getenv(2)), heap, stack, global variables

• Daemon process• Signals (sigaction(2)/signal(3))

• We learned how to create process (fork(2)) execute a run time (execXXX(2))

• How to wait(2) and waitpid(2) for process • We tried 2 methods of Inter process communications IPC

(network and UNIX domain sockets) - THERE ARE MANY MORE

• We understand process environment - File descriptor table, environment (getenv(2)), heap, stack, global variables

• Daemon process• Signals (sigaction(2)/signal(3))

Topics we covered - Threads

Topics we covered - Threads

• We learned to create POSIX & SDL threads• We learned to join threads• We learned to sync threads using

• POSIX & SDL cond• POSIX & SDL mutex

• We know what re-enterant and non-reenterant function is (strtok(3) and strtok_r(3))

• We discussed (in lecture) some syncing algorithms

• We learned to create POSIX & SDL threads• We learned to join threads• We learned to sync threads using

• POSIX & SDL cond• POSIX & SDL mutex

• We know what re-enterant and non-reenterant function is (strtok(3) and strtok_r(3))

• We discussed (in lecture) some syncing algorithms

Topics we covered - Files

Topics we covered - Files

• We know what file descriptor is (and to dup(2) it)• We know how to open(2) and close(2) fd• We know how to read(2) write(2) and lseek(2)

files• We know how to stat(2) to get file info• We know how to unlink(2) to delete file or UDS.• We know how to mmap(2) munmap(2) and

msync(2) files• We also know open/scan/readdir(2) API

• We know what file descriptor is (and to dup(2) it)• We know how to open(2) and close(2) fd• We know how to read(2) write(2) and lseek(2)

files• We know how to stat(2) to get file info• We know how to unlink(2) to delete file or UDS.• We know how to mmap(2) munmap(2) and

msync(2) files• We also know open/scan/readdir(2) API

Topics we covered - networking

Topics we covered - networking

• Behavior of • AF_INET, AF_UNIX• SOCK_STREAM, SOCK_DGRAM

• socket(2), bind(2), listen(2),accept(2), connect(2), send(2), recv(2), close(2) and shutdown(2)

• sendto(2) and recvfrom(2)• select(2)

• Behavior of • AF_INET, AF_UNIX• SOCK_STREAM, SOCK_DGRAM

• socket(2), bind(2), listen(2),accept(2), connect(2), send(2), recv(2), close(2) and shutdown(2)

• sendto(2) and recvfrom(2)• select(2)

Topics we covered UNIX

Topics we covered UNIX

• At this point I assume you all know how to • Edit a file• Compile a project• Create make file • Run user commands efficiently• Read a manpage• Get the unix time(2)

• Hopefully you should also be able to • Debug you code• Generate core dump and process it• Run strace(1) on a running server and see what’s up

• At this point I assume you all know how to • Edit a file• Compile a project• Create make file • Run user commands efficiently• Read a manpage• Get the unix time(2)

• Hopefully you should also be able to • Debug you code• Generate core dump and process it• Run strace(1) on a running server and see what’s up

Revisited topics - execXXX

Revisited topics - execXXX

• Refs• 8.9 in APUE 1st edition (p 207-212)• 8.10 in APUE 2nd edition (p 231-237)

• Family of 6 functions (execlp, execvp, execv, execl, execve, execle) execve is the most generic (lowest layer)

• Those function replace the running image of the current process with new one

• Refs• 8.9 in APUE 1st edition (p 207-212)• 8.10 in APUE 2nd edition (p 231-237)

• Family of 6 functions (execlp, execvp, execv, execl, execve, execle) execve is the most generic (lowest layer)

• Those function replace the running image of the current process with new one

Exec functionsExec functions

• Suffixes • The function with l suffix builds argv• The functions with the e suffix allow to

change environ• The functions with the p suffix try each path

in PATH environment variable (so if we run ls it will find /bin/ls)

• Suffixes • The function with l suffix builds argv• The functions with the e suffix allow to

change environ• The functions with the p suffix try each path

in PATH environment variable (so if we run ls it will find /bin/ls)

Exec functionsExec functions

• What does replace the current process image means?• The process has it’s memory space (data and program itself)

released. Instead a new program is loaded. • When the new program terminates the process terminates. • There is no way to get back to the old program or to get its

data

• Though it is by no means a must typical use of exec involves a call to fork(2) and wait(2)

• This is the way your shell (bash(1) or tcsh(1)) calls your programs

• What does replace the current process image means?• The process has it’s memory space (data and program itself)

released. Instead a new program is loaded. • When the new program terminates the process terminates. • There is no way to get back to the old program or to get its

data

• Though it is by no means a must typical use of exec involves a call to fork(2) and wait(2)

• This is the way your shell (bash(1) or tcsh(1)) calls your programs

System(3) - exec example

System(3) - exec example

int my_system (const char *command) { int pid, status;

if ((pid = fork()) == -1) return -1; if (pid == 0) { char *argv[4]; argv[0] = "sh"; argv[1] = "-c"; argv[2] = command; argv[3] = 0; execve("/bin/sh", argv, environ); }

waitpid(pid,&status,0);return status;

}

int my_system (const char *command) { int pid, status;

if ((pid = fork()) == -1) return -1; if (pid == 0) { char *argv[4]; argv[0] = "sh"; argv[1] = "-c"; argv[2] = command; argv[3] = 0; execve("/bin/sh", argv, environ); }

waitpid(pid,&status,0);return status;

}

System (cont’d)System (cont’d)

} do { if (waitpid(pid, &status, 0) == -1) { if (errno != EINTR) return -1; } else return status; } while(1); }// Note that system(3) is not very recommended function and I prefer you will use the

above // instead of system(3) in your homework (but using system is legal)// the above code is from the BUGS section of man system. It is suggested as

replacement// I suggest you follow the advice

} do { if (waitpid(pid, &status, 0) == -1) { if (errno != EINTR) return -1; } else return status; } while(1); }// Note that system(3) is not very recommended function and I prefer you will use the

above // instead of system(3) in your homework (but using system is legal)// the above code is from the BUGS section of man system. It is suggested as

replacement// I suggest you follow the advice

POSIX condPOSIX cond

• Ref : APUE 2nd edition (doesn’t appear on first) 11.6 (specifically p 382-385)

• We know of mutex - I came first therefore it is mine.• But lets think of the following scenarios (hint -

homework 2)• I have a file being received and I need to compress

it/uncompress it when receiving is done • I have a file being compressed. I have to wake up some

threads that will send the file but only after compression is done

• Ref : APUE 2nd edition (doesn’t appear on first) 11.6 (specifically p 382-385)

• We know of mutex - I came first therefore it is mine.• But lets think of the following scenarios (hint -

homework 2)• I have a file being received and I need to compress

it/uncompress it when receiving is done • I have a file being compressed. I have to wake up some

threads that will send the file but only after compression is done

Cond Vs. MutexCond Vs. Mutex

• In Mutex case I am entering the critical section AND prevent other threads from entering there.

• In cond case I am blocking myself from entering the critical section. I release myself after another thread has finished preparing the critical section for me

• In Mutex case I am entering the critical section AND prevent other threads from entering there.

• In cond case I am blocking myself from entering the critical section. I release myself after another thread has finished preparing the critical section for me

Cond exampleCond example

• check out p384-385 of APUE 2e for a simpler example but their code is not a complete program

• In our example we will wait for child process to die. (that child process may have done some work for us… such as compress or uncompress file) then we wake up another thread when we are done

• check out p384-385 of APUE 2e for a simpler example but their code is not a complete program

• In our example we will wait for child process to die. (that child process may have done some work for us… such as compress or uncompress file) then we wake up another thread when we are done

Cond example - singal when child die

Cond example - singal when child die

pthread_cond_t readycond=PTHREAD_COND_INITIALIZER;pthread_mutex_t readymutex=PTHREAD_MUTEX_INIALIZER;

void * waitingThread(void * arg){

pthread_mutex_lock(&readymutex);printf (“before waiting for cond\n”);pthread_cond_wait(&readycond, &readymutex );printf (“after cond was relesaed\n);

// do somethingpthread_mutex_unlock(&readymutex);

}

pthread_cond_t readycond=PTHREAD_COND_INITIALIZER;pthread_mutex_t readymutex=PTHREAD_MUTEX_INIALIZER;

void * waitingThread(void * arg){

pthread_mutex_lock(&readymutex);printf (“before waiting for cond\n”);pthread_cond_wait(&readycond, &readymutex );printf (“after cond was relesaed\n);

// do somethingpthread_mutex_unlock(&readymutex);

}

Cond example 2/2Cond example 2/2

Int main(){

pthread_t tid;pthread_create(&tid,NULL,waitingThread,NULL);my_system(getenv(“program”)); pthread_mutex_lock(&readymutex);pthread_cond_signal(&readycond);pthread_mutex_unlock(&readymutex);

}

Int main(){

pthread_t tid;pthread_create(&tid,NULL,waitingThread,NULL);my_system(getenv(“program”)); pthread_mutex_lock(&readymutex);pthread_cond_signal(&readycond);pthread_mutex_unlock(&readymutex);

}

Cond function prototypes

Cond function prototypes

#include <pthread.h>

int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr);

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec *abstime);

#include <pthread.h>

int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *attr);

int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec *abstime);

Cond function prototypes 2/2

Cond function prototypes 2/2

#include <pthread.h>

int pthread_cond_signal(pthread_cond_t *cond);int pthread_cond_broadcast(pthread_cond_t

*cond);int pthread_cond_destroy(pthread_cond_t *cond);

#include <pthread.h>

int pthread_cond_signal(pthread_cond_t *cond);int pthread_cond_broadcast(pthread_cond_t

*cond);int pthread_cond_destroy(pthread_cond_t *cond);

Initializing conds and mutexes

Initializing conds and mutexes

• Using macros (PTHREAD_COND_INITIALIZER, PTHREAD_MUTEX_INITIALIZER)

• Using functions (pthread_mutex_init(2), pthread_cond_init(2))

• Unless you know better it is safe to give null for attributes.

• Cond and mutex attributes are discussed in 12.4 of APUE 2e and refer to things such as is the mutex recursive (i.e. if it is locked twice, by the same thread does it have to be released twice)

• Most attributes are beyond the scope for us.

• Using macros (PTHREAD_COND_INITIALIZER, PTHREAD_MUTEX_INITIALIZER)

• Using functions (pthread_mutex_init(2), pthread_cond_init(2))

• Unless you know better it is safe to give null for attributes.

• Cond and mutex attributes are discussed in 12.4 of APUE 2e and refer to things such as is the mutex recursive (i.e. if it is locked twice, by the same thread does it have to be released twice)

• Most attributes are beyond the scope for us.

Syncing methodsSyncing methods

For processes• We can use file locking to

implement mutex. (this doesn’t work for threads0

• We use IPC (for example UDS) to implement cond - We send one byte when we are ready. We select-recv that byte. Waiting in similar way to cond. (this also works between threads)

For processes• We can use file locking to

implement mutex. (this doesn’t work for threads0

• We use IPC (for example UDS) to implement cond - We send one byte when we are ready. We select-recv that byte. Waiting in similar way to cond. (this also works between threads)

For threads• We use mutex to lock

critical section• We use cond to lock

ourselves • These mechanisms do

not work on Processes!

For threads• We use mutex to lock

critical section• We use cond to lock

ourselves • These mechanisms do

not work on Processes!

DaemonsDaemons

• We want to run in background detached from any login shell.

• We fork(2) and kill parent to lose controlling terminal. (controlling terminal belongs to parent)

• We setsid(2) to detach from login. Then we fork(2) again to lose virtual terminal

• We want to run in background detached from any login shell.

• We fork(2) and kill parent to lose controlling terminal. (controlling terminal belongs to parent)

• We setsid(2) to detach from login. Then we fork(2) again to lose virtual terminal

AdditionsAdditions

• We usually like to set some signals to our daemon

• We like to reopen (using dup2) the stdXXX to /dev/null just in case somebody tries to print

• We like to chdir to (“/”) so that cwd can be removed. (will not be in use)

• Some daemonize functions do more things

• We usually like to set some signals to our daemon

• We like to reopen (using dup2) the stdXXX to /dev/null just in case somebody tries to print

• We like to chdir to (“/”) so that cwd can be removed. (will not be in use)

• Some daemonize functions do more things

SyslogSyslog

• Since we closed stdout and stderr we can’t print.

• Some programmers would like to print anyway…

• That’s why we use syslog – the UNIX logging facility for all daemons

• Since we closed stdout and stderr we can’t print.

• Some programmers would like to print anyway…

• That’s why we use syslog – the UNIX logging facility for all daemons

Tomer’s way to do ex. 2

Tomer’s way to do ex. 2

• What Tomer did was to use ffmpeg generalized reading methods to avoid transferring structs.

• He defined new protocol and registered it

• Then all that is left is to implement the protocol methods.

• What Tomer did was to use ffmpeg generalized reading methods to avoid transferring structs.

• He defined new protocol and registered it

• Then all that is left is to implement the protocol methods.

CLIENT IMPLEMENTATION

CLIENT IMPLEMENTATION

• All that the client now need to implement are the methods that are found in osetup.c

• Tomer has also provided methods that demonstrate using a local file using upex.c

• The osetup.c should now be overwritten to work with network. – thus you end up with a complete streaming client/server

• All that the client now need to implement are the methods that are found in osetup.c

• Tomer has also provided methods that demonstrate using a local file using upex.c

• The osetup.c should now be overwritten to work with network. – thus you end up with a complete streaming client/server

This to note in Tomer implementation

This to note in Tomer implementation

• Check main to see that the new protocol is registered.

• Implement communication protocol anyway you want.

• Check main to see that the new protocol is registered.

• Implement communication protocol anyway you want.

Starting next week we study kernel (AT LAST!)

Starting next week we study kernel (AT LAST!)