C/C++ 多线程同步和多进程日志问题

C++语言 码拜 7年前 (2015-07-10) 1374次浏览 0个评论

有两个问题想咨询一下,

1、多线程同步的问题,之前公司有一个后台服务是用多线程框架处理的,然后是一个网络线程和多个逻辑线程,这样当有请求来的时候是不是不能保证请求的时序问题,比如,某一个人在业务中首先有一个加10个钱币的请求,然后迅速有一个扣10个钱币的请求,会不会出现扣10个钱币的请求先返回,然后提示钱币不足?

2、多进程日志同步的问题,当启动多个进程处理逻辑的时候,多个进程都要打印日志到同一个文件,这个怎么处理同步问题,不然的话,肯定会乱序的

10分

仅供参考:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef WIN32
    #include <windows.h>
    #include <io.h>
#else
    #include <unistd.h>
    #include <sys/time.h>
    #include <pthread.h>
    #define  CRITICAL_SECTION   pthread_mutex_t
    #define  _vsnprintf         vsnprintf
#endif
//Log{
#define MAXLOGSIZE 20000000
#define MAXLINSIZE 16000
#include <time.h>
#include <sys/timeb.h>
#include <stdarg.h>
char logfilename1[]="MyLog1.log";
char logfilename2[]="MyLog2.log";
static char logstr[MAXLINSIZE+1];
char datestr[16];
char timestr[16];
char mss[4];
CRITICAL_SECTION cs_log;
FILE *flog;
#ifdef WIN32
void Lock(CRITICAL_SECTION *l) {
    EnterCriticalSection(l);
}
void Unlock(CRITICAL_SECTION *l) {
    LeaveCriticalSection(l);
}
#else
void Lock(CRITICAL_SECTION *l) {
    pthread_mutex_lock(l);
}
void Unlock(CRITICAL_SECTION *l) {
    pthread_mutex_unlock(l);
}
#endif
void LogV(const char *pszFmt,va_list argp) {
    struct tm *now;
    struct timeb tb;

    if (NULL==pszFmt||0==pszFmt[0]) return;
    _vsnprintf(logstr,MAXLINSIZE,pszFmt,argp);
    ftime(&tb);
    now=localtime(&tb.time);
    sprintf(datestr,"%04d-%02d-%02d",now->tm_year+1900,now->tm_mon+1,now->tm_mday);
    sprintf(timestr,"%02d:%02d:%02d",now->tm_hour     ,now->tm_min  ,now->tm_sec );
    sprintf(mss,"%03d",tb.millitm);
    printf("%s %s.%s %s",datestr,timestr,mss,logstr);
    flog=fopen(logfilename1,"a");
    if (NULL!=flog) {
        fprintf(flog,"%s %s.%s %s",datestr,timestr,mss,logstr);
        if (ftell(flog)>MAXLOGSIZE) {
            fclose(flog);
            if (rename(logfilename1,logfilename2)) {
                remove(logfilename2);
                rename(logfilename1,logfilename2);
            }
        } else {
            fclose(flog);
        }
    }
}
void Log(const char *pszFmt,...) {
    va_list argp;

    Lock(&cs_log);
    va_start(argp,pszFmt);
    LogV(pszFmt,argp);
    va_end(argp);
    Unlock(&cs_log);
}
//Log}
int main(int argc,char * argv[]) {
    int i;
#ifdef WIN32
    InitializeCriticalSection(&cs_log);
#else
    pthread_mutex_init(&cs_log,NULL);
#endif
    for (i=0;i<10000;i++) {
        Log("This is a Log %04d from FILE:%s LINE:%d\n",i, __FILE__, __LINE__);
    }
#ifdef WIN32
    DeleteCriticalSection(&cs_log);
#else
    pthread_mutex_destroy(&cs_log);
#endif
    return 0;
}
//1-78行添加到你带main的.c或.cpp的那个文件的最前面
//81-85行添加到你的main函数开头
//89-93行添加到你的main函数结束前
//在要写LOG的地方仿照第87行的写法写LOG到文件MyLog1.log中

10分

进程生成的不同日志合并后按每行开头的时间戳排序即可。
 
引用 2 楼 zhao4zhong1 的回复:

进程生成的不同日志合并后按每行开头的时间戳排序即可。

不是排序的问题,多进程同时操作一个文件,有可能两条三条日志打印在一行的错乱

10分

多进程锁使用Mutex

CreateMutex
The CreateMutex function creates a named or unnamed mutex object.

HANDLE CreateMutex(
LPSECURITY_ATTRIBUTES lpMutexAttributes,
// pointer to security attributes
BOOL bInitialOwner, // flag for initial ownership
LPCTSTR lpName // pointer to mutex-object name
);

Parameters
lpMutexAttributes
Pointer to a SECURITY_ATTRIBUTES structure that determines whether the returned handle can be inherited by child processes. If lpMutexAttributes is NULL, the handle cannot be inherited.
Windows NT: The lpSecurityDescriptor member of the structure specifies a security descriptor for the new mutex. If lpMutexAttributes is NULL, the mutex gets a default security descriptor.

bInitialOwner
Specifies the initial owner of the mutex object. If this value is TRUE and the caller created the mutex, the calling thread obtains ownership of the mutex object. Otherwise, the calling thread does not obtain ownership of the mutex. To determine if the caller created the mutex, see the Return Values section.
lpName
Pointer to a null-terminated string specifying the name of the mutex object. The name is limited to MAX_PATH characters and can contain any character except the backslash path-separator character (\). Name comparison is case sensitive.
If lpName matches the name of an existing named mutex object, this function requests MUTEX_ALL_ACCESS access to the existing object. In this case, the bInitialOwner parameter is ignored because it has already been set by the creating process. If the lpMutexAttributes parameter is not NULL, it determines whether the handle can be inherited, but its security-descriptor member is ignored.

If lpName is NULL, the mutex object is created without a name.

If lpName matches the name of an existing event, semaphore, waitable timer, job, or file-mapping object, the function fails and the GetLastError function returns ERROR_INVALID_HANDLE. This occurs because these objects share the same name space.

Return Values
If the function succeeds, the return value is a handle to the mutex object. If the named mutex object existed before the function call, the function returns a handle to the existing object and GetLastError returns ERROR_ALREADY_EXISTS. Otherwise, the caller created the mutex.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks
The handle returned by CreateMutex has MUTEX_ALL_ACCESS access to the new mutex object and can be used in any function that requires a handle to a mutex object.

Any thread of the calling process can specify the mutex-object handle in a call to one of the wait functions. The single-object wait functions return when the state of the specified object is signaled. The multiple-object wait functions can be instructed to return either when any one or when all of the specified objects are signaled. When a wait function returns, the waiting thread is released to continue its execution.

The state of a mutex object is signaled when it is not owned by any thread. The creating thread can use the bInitialOwner flag to request immediate ownership of the mutex. Otherwise, a thread must use one of the wait functions to request ownership. When the mutex””s state is signaled, one waiting thread is granted ownership, the mutex””s state changes to nonsignaled, and the wait function returns. Only one thread can own a mutex at any given time. The owning thread uses the ReleaseMutex function to release its ownership.

The thread that owns a mutex can specify the same mutex in repeated wait function calls without blocking its execution. Typically, you would not wait repeatedly for the same mutex, but this mechanism prevents a thread from deadlocking itself while waiting for a mutex that it already owns. However, to release its ownership, the thread must call ReleaseMutex once for each time that the mutex satisfied a wait.

Two or more processes can call CreateMutex to create the same named mutex. The first process actually creates the mutex, and subsequent processes open a handle to the existing mutex. This enables multiple processes to get handles of the same mutex, while relieving the user of the responsibility of ensuring that the creating process is started first. When using this technique, you should set the bInitialOwner flag to FALSE; otherwise, it can be difficult to be certain which process has initial ownership.

Multiple processes can have handles of the same mutex object, enabling use of the object for interprocess synchronization. The following object-sharing mechanisms are available:

A child process created by the CreateProcess function can inherit a handle to a mutex object if the lpMutexAttributes parameter of CreateMutex enabled inheritance.
A process can specify the mutex-object handle in a call to the DuplicateHandle function to create a duplicate handle that can be used by another process.
A process can specify the name of a mutex object in a call to the OpenMutex or CreateMutex function.
Use the CloseHandle function to close the handle. The system closes the handle automatically when the process terminates. The mutex object is destroyed when its last handle has been closed.

Windows CE: The lpMutexAttributes parameter must be set to NULL.

QuickInfo
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Requires version 1.0 or later.
Header: Declared in winbase.h.
Import Library: Use kernel32.lib.
Unicode: Implemented as Unicode and ANSI versions on Windows NT.

See Also
Synchronization Overview, Synchronization Functions, CloseHandle, CreateProcess, DuplicateHandle, OpenMutex, ReleaseMutex, SECURITY_ATTRIBUTES

10分

_locking也可以凑合用:
_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

 
Linux下有一个flock文件锁,或者fcntl段级别的锁
 
就用锁实现吧
 
赵老师说的应该是window上的锁,感觉很高端的样子

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