user-0 提问: 多程序写一个文件/文件的并行写入如何处理？

回复:
user: user-1
content: 文件可以加锁(Windows,unix,linux?)， 文件可以共享读，写方式打开，共享的文件，可以锁住某一部分(文件锁)。  如果你使用DOS早期版本，另说。。。 不过早期版本的DOS， 只能同时运行一个程序，多个程序同时运行很困难。

user: user-2
content: _locking Locks or unlocks bytes of a file.  int _locking( int handle, int mode, long nbytes );  Routine Required Header Optional Headers Compatibility  _locking <io.h> and <sys/locking.h> <errno.h> Win 95, Win NT    For additional compatibility information, see Compatibility in the Introduction.  Libraries  LIBC.LIB Single thread static library, retail version  LIBCMT.LIB Multithread static library, retail version  MSVCRT.LIB Import library for MSVCRT.DLL, retail version    Return Value  _locking returns 0 if successful. A return value of –1 indicates failure, in which case errno is set to one of the following values:  EACCES  Locking violation (file already locked or unlocked).  EBADF  Invalid file handle.  EDEADLOCK  Locking violation. Returned when the _LK_LOCK or _LK_RLCK flag is specified and the file cannot be locked after 10 attempts.  EINVAL  An invalid argument was given to _locking.  Parameters  handle  File handle  mode  Locking action to perform  nbytes  Number of bytes to lock  Remarks  The _locking function locks or unlocks nbytes bytes of the file specified by handle. Locking bytes in a file prevents access to those bytes by other processes. All locking or unlocking begins at the current position of the file pointer and proceeds for the next nbytes bytes. It is possible to lock bytes past end of file.  mode must be one of the following manifest constants, which are defined in LOCKING.H:  _LK_LOCK  Locks the specified bytes. If the bytes cannot be locked, the program immediately tries again after 1 second. If, after 10 attempts, the bytes cannot be locked, the constant returns an error.  _LK_NBLCK  Locks the specified bytes. If the bytes cannot be locked, the constant returns an error.  _LK_NBRLCK  Same as _LK_NBLCK.  _LK_RLCK  Same as _LK_LOCK.  _LK_UNLCK  Unlocks the specified bytes, which must have been previously locked.  Multiple regions of a file that do not overlap can be locked. A region being unlocked must have been previously locked. _locking does not merge adjacent regions; if two locked regions are adjacent, each region must be unlocked separately. Regions should be locked only briefly and should be unlocked before closing a file or exiting the program.  Example  /* LOCKING.C: This program opens a file with sharing. It locks  * some bytes before reading them, then unlocks them. Note that the  * program works correctly only if the file exists.  */  #include <io.h> #include <sys/types.h> #include <sys/stat.h> #include <sys/locking.h> #include <share.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h>  void main( void ) {    int  fh, numread;    char buffer[40];     /* Quit if can't open file or system doesn't      * support sharing.      */    fh = _sopen( "locking.c", _O_RDWR, _SH_DENYNO,                   _S_IREAD | _S_IWRITE );    if( fh == -1 )       exit( 1 );     /* Lock some bytes and read them. Then unlock. */    if( _locking( fh, LK_NBLCK, 30L ) != -1 )    {       printf( "No one can change these bytes while I'm reading them\n" );       numread = _read( fh, buffer, 30 );       printf( "%d bytes read: %.30s\n", numread, buffer );       lseek( fh, 0L, SEEK_SET );      _locking( fh, LK_UNLCK, 30L );       printf( "Now I'm done. Do what you will with them\n" );    }    else       perror( "Locking failed\n" );     _close( fh ); }   Output  No one can change these bytes while I'm reading them 30 bytes read: /* LOCKING.C: This program ope Now I'm done. Do what you will with them   File Handling Routines  See Also   _creat, _open

user: user-2
content: 改为多程序通过多个数据库连接写数据库表。

user: user-3
content: 学习下 ……

user: user-4
content: 这些并行的程序如果是代码可控的话,可以把文件操作封装成一个动态库,通过内核级全局锁操作文件,可以保证数据无误,这样一来,就把并行变成同步了

user: user-0
content: 引用 3 楼 u011704121 的回复:其实可以把所有要写的东西排队，只有一个程序可以写，别的程序想写，就发送给他就行  可否再描述详细一点？我一会在做一般的C编程，排队、发送什么的概念有点陌生

user: user-0
content: 引用 4 楼 mujiok2003 的回复:[quote=引用 2 楼 gong_xufei 的回复:] [quote=引用 1 楼 mujiok2003 的回复:] 1. 打开文件的时候可以指明是否是独占 2. 在共享模式下,由操作系统保证同步.  多谢解答。 但实现上还是不很明白，别处也没搜索到： （1）如何指明是否独占？ （2）共享模式是否需要在程序中进行实现？如何实现？ 这两个问题貌似是一个。。。 PS：我做的是linux上的C编程 谢谢！[/quote]  http://linux.die.net/man/2/open[/quote]  貌似很强大的样子，先研究一下。

user: user-5
content: 引用 2 楼 gong_xufei 的回复:[quote=引用 1 楼 mujiok2003 的回复:] 1. 打开文件的时候可以指明是否是独占 2. 在共享模式下,由操作系统保证同步.  多谢解答。 但实现上还是不很明白，别处也没搜索到： （1）如何指明是否独占？ （2）共享模式是否需要在程序中进行实现？如何实现？ 这两个问题貌似是一个。。。 PS：我做的是linux上的C编程 谢谢！[/quote]  http://linux.die.net/man/2/open

user: user-6
content: 其实可以把所有要写的东西排队，只有一个程序可以写，别的程序想写，就发送给他就行

user: user-0
content: 引用 1 楼 mujiok2003 的回复:1. 打开文件的时候可以指明是否是独占 2. 在共享模式下,由操作系统保证同步.  多谢解答。 但实现上还是不很明白，别处也没搜索到： （1）如何指明是否独占？ （2）共享模式是否需要在程序中进行实现？如何实现？ 这两个问题貌似是一个。。。 PS：我做的是linux上的C编程 谢谢！

user: user-5
content: 1. 打开文件的时候可以指明是否是独占 2. 在共享模式下,由操作系统保证同步.