20170310 [學習筆記] Linux 系統程式 (2)

• 一、作業系統
  • (一) Process in Memory
  • (二) Process State
  • (三) Process Control Block (PCB)
  • (四) Process Switch
  • (五) Process、Thread
  • (六) Process Scheduling
    • Schedulers
    • Processes
  • (七) Process Creation
• 二、Linux 程式設計
  • (一) Unix system call
    • 1. execv()
  • (二) Signals
    • 1. UNIX Process Control
    • 2. kill Command
    • 3. Function Call
    • 4. Linux Signal
    • 5. 訊號處理 - signal.h
      • (1) signal()
      • (2) sigaction()

一、作業系統

• 課程簡報 - Ch3：Process Concept

(一) Process in Memory

(二) Process State

• new: The process is being created.
• running: Instructions are being executed.
• waiting: The process is waiting for some event to occur.
• ready: The process is waiting to be assigned to a processor.
• terminated: The process has finished execution.

(三) Process Control Block (PCB)

(四) Process Switch

(五) Process、Thread

• 參考資料
  • Program / Process / Thread 的差別
  • “Process 行程”、”Thread 執行緒”、”Multithreading 多執行緒” 簡介

(六) Process Scheduling

• Process scheduler selects among available processes for next execution on CPU.
• Maintains scheduling queues of processes.
  • Job queue – set of all processes in the system.
  • Ready queue – set of all processes residing in main memory, ready and waiting to execute.
  • Device queues – set of processes waiting for an I/O device.
  • Processes migrate among the various queues.

Schedulers

• Long-term scheduler (or job scheduler) – selects which processes should be brought into the ready queue.
• Short-term scheduler (or CPU scheduler) – selects which process should be executed next and allocates CPU.
  • Sometimes the only scheduler in a system.
• The long-term scheduler controls the degree of multiprogramming.
• Medium-term scheduler can be added if degree of multiple programming needs to decrease.
  • Remove process from memory, store on disk, bring back in from disk to continue execution: swapping.

Degree of multiprogramming：多工程度、記憶體中行程的總數量

Processes

• I/O-bound process – spends more time doing I/O than computations, many short CPU bursts.
  • 行程大部份的時間在做 I/O，只有少部份的時間在做計算。
• CPU-bound process – spends more time doing computations; few very long CPU bursts.
  • 行程大部份的時間在做計算，只有少部份的時間在做 I/O。

(七) Process Creation

• UNIX examples
  • fork()：system call creates new process
  • exec()：system call used after a fork() to replace the process’ memory space with a new program

• 課程作業

#include <sys/types.h>
#include <stdio.h>
#include <unistd.h>

int main(void) {
	pid_t pid;
	
/* fork a child process */
	pid = fork();

	if (pid < 0) {		// erro occurred
		fprintf(stderr, "Fork Failed");
		return 1;
	}
	else if (pid == 0) {	// child process
		execlp("/bin/ls", "ls", NULL);
	}
	else {			// parent process
		// parent will wait for the child to complete
		wait(NULL);
		printf("Child Complete\n");
	}	
	return 0;
}

• 執行結果

二、Linux 程式設計

• 課程簡報 - Creating and Executing Processes
• 課程簡報 - Signal

(一) Unix system call

1. execv()

• 課堂練習： execv() 的概念

#include <stdio.h>
#include <stdlib.h>

char * argv[] = {"/bin/ls", "-1", 0};
int main(void) {

	int pid, status;

	if ((pid = fork()) < 0) {
		printf("Fork error \n");
		exit(1);
	}
	
	if (pid == 0) {	/* Child executes here */
		execv (argv[0], argv);
		printf("Exec error \n");
		exit(1);
	} else		/* Parent executes here */
		wait(&status);

	printf("Hello there! \n");
	return 0;
}

(二) Signals

1. UNIX Process Control

2. kill Command

kill -signal pid

• Example
  • kill –2 1234
  • kill -SIGINT 1234
    • Same as pressing Ctrl-c if process 1234 is running in foreground.

3. Function Call

• raise()

int ret = raise(SIGINT); /* Process commits suicide. */
assert(ret != 0);	/* Shouldn't get here. */

• kill()

int kill(pid_t iPid, int iSig);

pid_t iPid = getpid(); /* Process gets its id.*/
kill(iPid, SIGINT);	/* Process sends itself a SIGINT signal (commits suicide?) */

4. Linux Signal

• Linux Signal 種類
  • Ctrl-C (in older Unixes, DEL)
    • sends an INT signal (SIGINT)
    • by default, this causes the process to terminate.
  • Ctrl-Z
    • sends a TSTP signal (SIGTSTP)
    • by default, this causes the process to suspend execution.
  • Ctrl-
    • sends a QUIT signal (SIGQUIT)
    • by default, this causes the process to terminate and dump core.

5. 訊號處理 - signal.h

• 意義說明
  • SIGABORT 程序停止
  • SIGALRM 警示
  • SIGFPE 浮點數例外
  • SIGHUP 掛斷
  • SIGILL 非法指令
  • SIGINT 終端機插斷

(1) signal()

#include <signal.h>
void(*signal(int sig, void (*func)(int)))(int);

• 攔截 Ctrl-C 訊號

#include <signal.h>
#include <stdio.h>
#include <unistd.h>

void ouch(int sig) {
	printf("OUCH! - I got signal %d\n", sig);
	(void) signal(SIGINT, SIG_DFL);
}

int main(void) {
	(void) signal(SIGINT, ouch);
	
	while(1) {
		printf("Hello World!\n");
		sleep(1);
	}
}

(2) sigaction()

#include <signal.h>
int sigaction(int sig,const struct sigaction *act, struct sigaction *oact);

• 參數說明
  • sig: 要處理的訊號,若 act 指針非空, 則根據 act 修改該信號的處理動作；若 oact 指針非空, 則通過 oact 傳出該信號原來的處理動作。
  • void(*)(int) sa_handler
  • sigset_t sa_mask
  • int sa_flags
  • sa_handler 代表新的信號處理。
  • sa_mask 用來設置在處理該信號時暫時將 sa_mask 指定的信號集擱置。
  • sa_flags 用來設置信號處理的其他相關操作。
• 程式作業：signal 的處理

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>


// When the process get the "Ctrl+C" signal.
void show_time() {
    system("date"); // show the time.
}

// When the process gets the "Ctrl+\" signal.
void go_default() {
    signal(SIGINT, SIG_DFL);    // recover "Ctrl+C"
}


int main(void) {

    signal(SIGINT, show_time);  // triggering "Ctrl+C"
    signal(SIGQUIT, go_default);// triggering "Ctrl+\"

    while(1) {
        printf("What time is it？\n");  // Something interesting will happen if this line without "\n".
        sleep(1);
    }   
}

• 執行結果