Advanced Programming in the UNIX Environment

1
Advanced Programmingin the UNIX Environment

• Chap 1. Introduction
• 2003. 5. 1
• Daewoo Lee

2
Programs and Processes

• Program
• An executable file residing in a disk file
• Process
• An executing instance of a program
• Process ID unique nonnegative integer
  identifier of each process
• Process Control
• fork
• exec
• waitpid

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Process Control (1/2)

• fork
• To create a new process
• parent(caller), child(callee)
• Return value
• To parent pID of the new child
• To child 0
• Called once but returns twice.
• exec
• To execute the new program file
• Replace the current process with the new program
• 6 variants
• execl, execlp, execle, execv, execvp, execve

4
Process Control (2/2)

• fork exec
• Spawning a new process
• waitpid
• To wait for some process to terminate
• Return the termination status to the 2nd
  argument.

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ANSI C Features

• Primitive System Data Types
• ex. pid_t, size_t,
• ltsys/types.hgt
• To prevent from using specific data types
• To allow each implementation to choose a suitable
  data type
• Necessary to modify one header

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Error Handling

• When an error occurs
• A negative value is often returned.
• Additional information
• lterrno.hgt extern int errno
• errno
• Never cleared if an error doesnt occur.
• Never set to 0.
• strerror, perror

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Signals

• Signals
• To notify a process that some condition has
  occurred
• When a signal is received, the process can
• ignore the signal.
• let the default action occur.
• provide a function that is called when the signal
  occurs.
• signal catch the specific signal

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System Calls and Library Functions
Application Code
more elaborate interface
user process
C Library Functions
minimal interface
kernel