请问可以在数个线程中同时对一个文件使用open()函数和read()函数吗?

menzi11 2013-02-22 05:31:27

请问可以在不同线程中同时对一个文件使用open()函数和read()函数吗?
比如:



//Thread1:

int a = open("c:/1.txt",O_RDONLY);



//Thread2:

int a = open("c:/1.txt",O_RDONLY);

又或者:





int main()

{

    int a = open("c:/1.txt",O_RDONLY);

}



//Thread1:

read(a,ptr,100);



//Thread2:

read(a,ptr,100);

谢谢!

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赵4老师 2013-02-22

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仅供参考： _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