UNIX编程(7)-进程环境

1.main 函数

c程序总是从main函数开始执行，当内核执行c程序时，在调用main前先调用一个特殊的启动例程，启动例程从内核获得命令行参数和环境变量值，然后为按上述方式调用main做好安排

2.进程终止

有8种方式使进程终止：

1）从main返回

2）调用exit

3）调用_exit或_Exit

4）最后一个线程从其启动例程返回

5）最后一个线程调用pthread_exit

6)调用abort

7)接到一个信号并终止

8）最后一个线程对取消请求做出相应

有三个函数用来正常终止一个程序

#include <stdlib.h>

void exit(int status);

void _Exit(int status);

#include <unistd.h>

void _exit(int status);

_exit和_EXit立即进入内核，exit则先执行一些清理处理。

atexit函数用来登记终止处理程序

#include <stdlib.h>

int atexit(void (*func)(void));

例：

#include "apue.h"

static void my_exit1(void);
static void my_exit2(void);

int
main(void)
{
     if (atexit(my_exit2) != 0)
         err_sys("can't register my_exit2");

     if (atexit(my_exit1) != 0)
         err_sys("can't register my_exit1");

     if (atexit(my_exit1) != 0)
         err_sys("can't register my_exit1");

     printf("main is done\n");
     return(0);
}

static void
my_exit1(void)
{
   printf("first exit handler\n");
}

static void
my_exit2(void)
{
   printf("second exit handler\n");
}

3.命令行参数（略）

4.环境表

5.c程序的存储空间

6.共享库

7.存储器分配

#include <stdlib.h>

void *malloc(size_t size);

void *calloc(size_t nobj, size_t size);

void *realloc(void *ptr, size_t newsize);

All three return: non-null pointer if OK, NULL on error

void free(void *ptr);

8.环境变量

用于环境变量的操作函数

#include <stdlib.h>

char *getenv(const char *name);

#include <stdlib.h>

  int putenv(char *str);

  int setenv(const char *name, const char *value,
int rewrite);

  int unsetenv(const char *name);

9.setjmp和longjmp跨越函数跳转

#include <setjmp.h>

  int setjmp(jmp_buf env);

Returns: 0 if called directly, nonzero if returning from a call to longjmp

  void longjmp(jmp_buf env, int val);

例：

#include "apue.h"
#include <setjmp.h>

static void f1(int, int, int, int);
static void f2(void);

static jmp_buf jmpbuffer;
static int     globval;

int
main(void)
{
     int             autoval;
     register int    regival;
     volatile int    volaval;
     static int      statval;

     globval = 1; autoval = 2; regival = 3; volaval = 4; statval = 5;

     if (setjmp(jmpbuffer) != 0) {
         printf("after longjmp:\n");
         printf("globval = %d, autoval = %d, regival = %d,"
             " volaval = %d, statval = %d\n",
             globval, autoval, regival, volaval, statval);
         exit(0);
     }

     /*
      * Change variables after setjmp, but before longjmp.
      */
     globval = 95; autoval = 96; regival = 97; volaval = 98;
     statval = 99;

     f1(autoval, regival, volaval, statval); /* never returns */
     exit(0);
}

static void
f1(int i, int j, int k, int l)
{
    printf("in f1():\n");
    printf("globval = %d, autoval = %d, regival = %d,"
        " volaval = %d, statval = %d\n", globval, i, j, k, l);
    f2();
}
static void
f2(void)
{
    longjmp(jmpbuffer, 1);
}

10.资源限制getrlimit和setrlimit

#include <sys/resource.h>

int getrlimit(int resource, struct rlimit *rlptr);

int setrlimit(int resource, const struct rlimit *rlptr);

例：

#include "apue.h"
#if defined(BSD) || defined(MACOS)
#include <sys/time.h>
#define FMT "%10lld "
#else
#define FMT "%10ld "
#endif
#include <sys/resource.h>

#define doit(name) pr_limits(#name, name)

static void pr_limits(char *, int);

int
main(void)
{

#ifdef  RLIMIT_AS
    doit(RLIMIT_AS);
#endif
    doit(RLIMIT_CORE);
    doit(RLIMIT_CPU);
    doit(RLIMIT_DATA);
    doit(RLIMIT_FSIZE);
#ifdef  RLIMIT_LOCKS
    doit(RLIMIT_LOCKS);
#endif
#ifdef  RLIMIT_MEMLOCK
    doit(RLIMIT_MEMLOCK);
#endif
    doit(RLIMIT_NOFILE);
#ifdef  RLIMIT_NPROC
    doit(RLIMIT_NPROC);
#endif
#ifdef  RLIMIT_RSS
    doit(RLIMIT_RSS);
#endif
#ifdef  RLIMIT_SBSIZE
    doit(RLIMIT_SBSIZE);
#endif
    doit(RLIMIT_STACK);
#ifdef  RLIMIT_VMEM
    doit(RLIMIT_VMEM);
#endif
    exit(0);
}

static void
pr_limits(char *name, int resource)
{
    struct rlimit limit;

    if (getrlimit(resource, &limit) < 0)
        err_sys("getrlimit error for %s", name);
    printf("%-14s ", name);
    if (limit.rlim_cur == RLIM_INFINITY)
        printf("(infinite) ");
    else
        printf(FMT, limit.rlim_cur);
    if (limit.rlim_max == RLIM_INFINITY)
        printf("(infinite)");
    else
        printf(FMT, limit.rlim_max);
    putchar((int)'\n');
}

UNIX编程(7)-进程环境

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