Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 43)

CS485G Spring 2015 43

(f) The only difference is the return value. For A, it is B’s process

identiﬁer (PID). For B, it is 0.

9. The exit() system call terminates the calling process.

(a) The return value is the status. By convention, 0 means success,

and any other value is a failure code.

(b) The program can register a cleanup function to call at exit by

using atexit(); one may register many such functions.

10. The wait() system call reaps the terminated child, collecting its ter-

mination status and freeing its space in kernel data structures.

(a) Until the parent calls wait(), the child is a zombie.

(b) If the parent terminates before reaping its children, the init

process reaps them.

waitpid() waits for a speciﬁc PID.

(d) wait() returns an integer that can be queried by WIFEXITED

and WEXITSTATUS, among other macros.

11. A process can completely reload itself to run a different program by

using one of the exec() family of calls, such as execl().

(a) The parameters to execXX() include a string indicating the ﬁle

holding the executable object ﬁle, a list of 0 or more parameters

to that program, and, optionally, an array of pointers to strings

indicating environment values of the form var=value.

(b) The initial stack, when main() is called, contains the (1) envi-

ronment strings, (2) the command-line parameters, (3) pointers

to 1, (4) pointers to 2, (5) a pointer to 3, (6) a pointer to 4, a count

of parameters.

49 Processes in Unix

1. Process 1 is always init.

(a) Starts login on each terminal.

(b) Starts daemons to do background work.

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Cirrus Logic CS485 Manual de usuario Pagina 43