What%20is%20a%20Process?

1
What is a Process?

• A process is an executing program and its
  necessary overhead
• a process is not a program by itself

2
Overview

• System Calls
• fork()
• wait()
• pipe()
• write()
• read()
• Examples

3
Process Creation

• fork()
• NAME
• fork()- create a new process
• SYNOPSIS
• include ltsys/types.hgt
• include ltunistd.hgt
• ?pid_t fork (void)
• RETURN VALUE
• success
• parent- child pid
• child- 0
• failure
• -1

4
fork() system call-example

• include ltsys/types.hgt
• include ltunistd.hgt
• include ltstdio.hgt
• main()
• printf ( ld parent process id ld\n,
  getpid(), getppid() )
• fork()
• printf ( \nld parent process id ld\n,
  getpid(), getppid() )

5
fork() system call-example

• 17619 parent process id 12729
• 17619 parent process id 12729
• 2372 parent process id 17619

6
fork()- program structure

• include ltsys/types.hgt
• include ltunistd.hgt
• include ltstdlib.hgt
• include ltstdio.hgt
• main( int argc, char argv )
• pid_t pid
• if ( ( pid fork() ) gt 0 )
• /parent/
• else if ( pid 0 )
• /child/
• else
• /cannot fork/
• exit( 0 )

7
wait() system call

• wait() - wait for the process whose pid reference
  is passed to finish executing
• SYNOPSIS
• include ltsys/types.hgt
• include ltsys/wait.hgt
• ?pid_t wait ( int stat_loc )
• The unsigned decimal integer process ID for
  which to wait.
• RETURN VALUE
• success- child pid
• failure- -1 and errno is set

8
wait()- program structure
include ltsys/types.hgt include
ltunistd.hgt include ltstdlib.hgt include
ltstdio.hgt main( int argc, char argv
) pid_t childPID if ( ( childPID fork() )
0 ) /child/ else /parent/ wa
it ( 0 ) exit( 0 )
9
pipe() system call

• pipe() - to create a read-write pipe that may
  later be used to communicate with a process we'll
  fork off.
• SYNOPSIS
• int pipe( pfd )
• int pfd2
• PARAMETER
• pfd is an array of 2 integers, which that will
  be used to save the two file descriptors used to
  access the pipe.
• RETURN VALUE
• 0 - success
• -1 - error.

10
pipe() - structure

• / first, define an array to store the two file
  descriptors /
• int pipes2
• / now, create the pipe /
• int rc pipe(pipes)
• if (rc -1) / pipe() failed /
• perror("pipe")
• exit(1)
• If the call to pipe() succeeded, a pipe will be
  created, pipes0 will contain the number of its
  read file descriptor, and pipes1 will contain
  the number of its write file descriptor.

11
write() system call

• write() - used to write data to a file or other
  object identified by a file descriptor.
• SYNOPSIS
• include ltsys/types.hgt
• size_t write(int fildes, const void buf,
  size_t nbyte)
• PARAMETER
• fildes is the file descriptor,
• buf is the base address of the area of memory
  that data is copied from,
• nbyte is the amount of data to copy.
• RETURN VALUE
• The return value is the actual amont of data
  written, if this differs from nbyte then
  something has gone wrong.

12
read() system call

• read() - read data from a file or other object
  identified by a file descriptor.
• SYNOPSIS
• include ltsys/types.hgt
• size_t read(int fildes,void buf, size_t
  nbyte)
• ARGUMENT
• fildes is the descriptor,
• buf is the base address of the memory area into
  which the data is read,
• nbyte is the maximum amount of data to read.
• RETURN VALUE
• The actual amount of data read from the file.
  The pointer is incremented by the amount of data
  read.

13
Questions