Processes

Processes!

Address Space

Proc Address Space

What is Copied Over?

Forkbomb

Process Flowchart

Utilities Unleashed

What are you going to learn?

  • What the fork-exec-wait pattern is.
  • Why we use it.
  • String Manipulation.

All Fork-Exec-Wait Code

pid_t pid = fork();
if(pid == -1){
	//fork failed
}else if(pid == 0){
	//I am the child
	exec(...)
}else{
	//I Am the parent
	wait(pid);
}

Exec Family

  • There are three modifiers/mnemonic
    • Either past a list or argv (null terminated array) of arguments
    • Search for the executable either in the current directory or in the path
    • Use the parent’s environment variables or use an environment setting

  • Here are the list exec
    • execl( path, arg, … ),execute the file in current directory
    • execlp( file, arg, … ), executes a file only searching in the path
    • execle( path, arg, …, envp[]), execute the file in path + environment settings

  • Pass an array of string as arguments
    • execv( path, argv[]), execute the file in current directory
    • execvp( file, argv[]), execute the file in the path only
    • execvpe( file, argv[]), envp[]) // environment setting

time

  • ./time <command> <args> ...
  • Try measuring the time of running sleep 2
  • Should use fork-exec scheme.
  • Should take care of programs do not terminate successfully.
  • Command line arguments are not limited two one.
  • Use the format.h functions to print out time/etc.

time Workflow

Workflow for time

Helper Functions

  • struct timespec
    • time_t tv_sec;
    • long tv_nsec;
    • tv_sec = 10, tv_nsec = 992300000 -> 10.9923 sec
  • int clock_gettime(clockid_t, timespec *);
    • clockid_t: should use CLOCK_MONOTONIC in this lab
  • return 0 when success, -1 otherwise

env

  • ./env [-n #] [key=val1,val2,...] [key2=val1,val2,...] ... -- cmd [args] ..
  • ./env -n 4 TZ=EST5EDT,CST6CDT,MST7MDT,PST8PDT -- date - execute date under environment TZ=EST5EDT, then TZ=CST6CDT, then TZ=MST7MDT, and finally TZ=PST8PDT
  • ./env -n 4 TEMP=EST5EDT,CST6CDT,MST7MDT,PST8PDT TZ=%TEMP -- date - why is this the same as above?

env Workflow

Environment Workflow

Helper Functions

  • int setenv(const char* name, const char* value,
    int overwrite)
  • char *getenv(const char *name)
  • Write a split function that can split string based on ,
  • Write a function that can find all %notation in a string
  • Extend that function so that you can replace variables
    with environment variables
  • Use getenv to get environment variables
  • Be familiar with: return array of strings, clear an array
    of strings-> camelCasers