多进程的共享空间疑问
apue.h
- C/C++ code
/* Our own header, to be included before all standard system headers */#ifndef _APUE_H#define _APUE_H#if defined(SOLARIS)#define _XOPEN_SOURCE 500 /* Single UNIX Specification, Version 2 for Solaris 9 */#define CMSG_LEN(x) _CMSG_DATA_ALIGN(sizeof(struct cmsghdr)+(x))#elif !defined(BSD)#define _XOPEN_SOURCE 600 /* Single UNIX Specification, Version 3 */#endif#include <sys/types.h> /* some systems still require this */#include <sys/stat.h>#include <sys/termios.h> /* for winsize */#ifndef TIOCGWINSZ#include <sys/ioctl.h>#endif#include <stdio.h> /* for convenience */#include <stdlib.h> /* for convenience */#include <stddef.h> /* for offsetof */#include <string.h> /* for convenience */#include <unistd.h> /* for convenience */#include <signal.h> /* for SIG_ERR */#define MAXLINE 4096 /* max line length *//* * Default file access permissions for new files. */#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)/* * Default permissions for new directories. */#define DIR_MODE (FILE_MODE | S_IXUSR | S_IXGRP | S_IXOTH)typedef void Sigfunc(int); /* for signal handlers */#if defined(SIG_IGN) && !defined(SIG_ERR)#define SIG_ERR ((Sigfunc *)-1)#endif#define min(a,b) ((a) < (b) ? (a) : (b))#define max(a,b) ((a) > (b) ? (a) : (b))/* * Prototypes for our own functions. */char *path_alloc(int *); /* {Prog pathalloc} */long open_max(void); /* {Prog openmax} */void clr_fl(int, int); /* {Prog setfl} */void set_fl(int, int); /* {Prog setfl} */void pr_exit(int); /* {Prog prexit} */void pr_mask(const char *); /* {Prog prmask} */Sigfunc *signal_intr(int, Sigfunc *); /* {Prog signal_intr_function} */int tty_cbreak(int); /* {Prog raw} */int tty_raw(int); /* {Prog raw} */int tty_reset(int); /* {Prog raw} */void tty_atexit(void); /* {Prog raw} */#ifdef ECHO /* only if <termios.h> has been included */struct termios *tty_termios(void); /* {Prog raw} */#endifvoid sleep_us(unsigned int); /* {Ex sleepus} */ssize_t readn(int, void *, size_t); /* {Prog readn_writen} */ssize_t writen(int, const void *, size_t); /* {Prog readn_writen} */void daemonize(const char *); /* {Prog daemoninit} */int s_pipe(int *); /* {Progs streams_spipe sock_spipe} */int recv_fd(int, ssize_t (*func)(int, const void *, size_t));/* {Progs recvfd_streams recvfd_sockets} */int send_fd(int, int); /* {Progs sendfd_streams sendfd_sockets} */int send_err(int, int, const char *); /* {Prog senderr} */int serv_listen(const char *); /* {Progs servlisten_streams servlisten_sockets} */int serv_accept(int, uid_t *); /* {Progs servaccept_streams servaccept_sockets} */int cli_conn(const char *); /* {Progs cliconn_streams cliconn_sockets} */int buf_args(char *, int (*func)(int, char **)); /* {Prog bufargs} */int ptym_open(char *, int); /* {Progs3 ptyopen_streams ptyopen_bsd ptyopen_linux} */int ptys_open(char *); /* {Progs3 ptyopen_streams ptyopen_bsd ptyopen_linux} */#ifdef TIOCGWINSZpid_t pty_fork(int *, char *, int, const struct termios *, const struct winsize *); /* {Prog ptyfork} */#endifint lock_reg(int, int, int, off_t, int, off_t); /* {Prog lockreg} */#define read_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLK, F_RDLCK, (offset), (whence), (len))#define readw_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLKW, F_RDLCK, (offset), (whence), (len))#define write_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLK, F_WRLCK, (offset), (whence), (len))#define writew_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLKW, F_WRLCK, (offset), (whence), (len))#define un_lock(fd, offset, whence, len) \ lock_reg((fd), F_SETLK, F_UNLCK, (offset), (whence), (len))pid_t lock_test(int, int, off_t, int, off_t); /* {Prog locktest} */#define is_read_lockable(fd, offset, whence, len) \ (lock_test((fd), F_RDLCK, (offset), (whence), (len)) == 0)#define is_write_lockable(fd, offset, whence, len) \ (lock_test((fd), F_WRLCK, (offset), (whence), (len)) == 0)void err_dump(const char *, ...); /* {App misc_source} */void err_msg(const char *, ...);void err_quit(const char *, ...);void err_exit(int, const char *, ...);void err_ret(const char *, ...);void err_sys(const char *, ...);void log_msg(const char *, ...); /* {App misc_source} */void log_open(const char *, int, int);void log_quit(const char *, ...);void log_ret(const char *, ...);void log_sys(const char *, ...);void TELL_WAIT(void); /* parent/child from {Sec race_conditions} */void TELL_PARENT(pid_t);void TELL_CHILD(pid_t);void WAIT_PARENT(void);void WAIT_CHILD(void);#endif /* _APUE_H */
apueerror.h
- C/C++ code
#include <errno.h> /* for definition of errno */#include <stdarg.h> /* ISO C variable aruments */#define MAXLINE 4096static void err_doit(int, int, const char *, va_list);/* * Nonfatal error related to a system call. * Print a message and return. */void err_ret(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, errno, fmt, ap); va_end(ap);}/* * Fatal error related to a system call. * Print a message and terminate. */void err_sys(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, errno, fmt, ap); va_end(ap); exit(1);}/* * Fatal error unrelated to a system call. * Error code passed as explict parameter. * Print a message and terminate. */void err_exit(int error, const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, error, fmt, ap); va_end(ap); exit(1);}/* * Fatal error related to a system call. * Print a message, dump core, and terminate. */void err_dump(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(1, errno, fmt, ap); va_end(ap); abort(); /* dump core and terminate */ exit(1); /* shouldn't get here */}/* * Nonfatal error unrelated to a system call. * Print a message and return. */void err_msg(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(0, 0, fmt, ap); va_end(ap);}/* * Fatal error unrelated to a system call. * Print a message and terminate. */void err_quit(const char *fmt, ...) { va_list ap; va_start(ap, fmt); err_doit(0, 0, fmt, ap); va_end(ap); exit(1);}/* * Print a message and return to caller. * Caller specifies "errnoflag". */static void err_doit(int errnoflag, int error, const char *fmt, va_list ap) { char buf[MAXLINE]; vsnprintf(buf, MAXLINE, fmt, ap); if (errnoflag) snprintf(buf + strlen(buf), MAXLINE - strlen(buf), ": %s", strerror( error)); strcat(buf, "\n"); fflush(stdout); /* in case stdout and stderr are the same */ fputs(buf, stderr); fflush(NULL); /* flushes all stdio output streams */}- C/C++ code
#include "apue.h"#include "apueerror.h"//./a.out > temp.out 会产生两次before forkint glob = 6; /* external variable in initialized data */char buf[] = "a write to stdout\n";int main(void) { int var; /* automatic variable on the stack */ pid_t pid; var = 88; if (write(STDOUT_FILENO, buf, sizeof(buf) - 1) != sizeof(buf) - 1) err_sys("write error"); printf("before fork\n"); /* we don't flush stdout */ if ((pid = fork()) < 0) { err_sys("fork error"); } else if (pid == 0) { /* child */ glob++; /* modify variables */ var++; } else { sleep(2); /* parent */ } printf("pid = %d, glob = %d, var = %d\n", getpid(), glob, var); exit(0);}为什么
./a.out 只会产生一次 before fork
./a.out > temp.out 会产生两次before fork
为什么重定向才会有两次呢？
[解决办法]
多进程用共享临时文本文件
[解决办法]
因为终端是行缓冲，文件是全缓冲，你的输出printf没有\n，所以fork的子进程的stdin._iobuf里也有那句话，两个进程都结束的时候冲刷缓冲区都写到这个文件里了。