各位大大，請教個問題 ，一個程式，需要快速保存4個傳感器的資料到本地檔案。如果我對每個傳感器添加一個執行緒，這樣使用4個執行緒來進行本地檔案的寫操作。這樣會不會有什么問題，多執行緒的磁盤寫操作有什么需要注意的事項沒？
uj5u.com熱心網友回復：
如果寫不同的檔案就無所謂了，如果是寫同一個檔案，你可以4個執行緒將要寫的資料往同一個鏈表尾部添加（做好執行緒同步),另開一個執行緒，從鏈表頭取資料往檔案中寫就可以了。uj5u.com熱心網友回復：
寫同一個檔案要加鎖uj5u.com熱心網友回復：
_lockingLocks 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
uj5u.com熱心網友回復：
在檔案大小相同的前提下：讀剛讀過的檔案比頭次讀沒讀過的檔案快
讀轉速快的硬碟上的檔案比讀轉速慢的硬碟上的檔案快
讀沒有磁盤碎片的檔案比讀有磁盤碎片的檔案快
讀檔案不處理比邊讀邊處理快
單執行緒從頭到尾一次讀檔案比多執行緒分別讀檔案各部分快（非固態硬碟上）
讀固態硬碟上的檔案比讀普通硬碟上的檔案快
寫類似。
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標籤：進程/線程/DLL