学习使用Depend工具,#pragma, Mutex，Event

1.

可以方便的看到哪些模块，关联到了这个dll，

/Program Files/Microsoft Visual Studio 8/Common7/Tools/Bin/depends.exe

具体分析待阅读：

http://www.vckbase.com/document/viewdoc/?id=1590

2. pragmatics 语法论

vc下的编译使用命令：

#pragma comment(lib,"dll_name.lib") 隐式链接dll_name.lib

可以在头文件中写入上边的语句，然后，

class __declspec(dllimport) CMyClassName

{

.........

}

3. 使用Mutex，防止进程或线程间的同时操作一个资源。

Copy From MSDN

Using Mutex Objects

You can use a mutex object to protect a
shared resource from simultaneous access by multiple threads or processes. Each
thread must wait for ownership of the mutex before it can execute the code that
accesses the shared resource. For example, if several threads share access to a
database, the threads can use a mutex object to permit only one thread at a time
to write to the database.

In the following example, a process uses the CreateMutex function to create a mutex
object.

HANDLE hMutex;

// Create a mutex with no initial owner.

hMutex = CreateMutex(
NULL,                       // default security attributes
FALSE,                      // initially not owned
NULL);                      // unnamed mutex

if (hMutex == NULL)
{
printf("CreateMutex error: %d/n", GetLastError());
}

When a thread of this process writes to the database, as in the next example,
it first requests ownership of the mutex. If it gets ownership, the thread
writes to the database and then releases its ownership.

The example uses structured exception-handling syntax to ensure that the
thread properly releases the mutex object. The __finally block of code is
executed no matter how the __try block terminates (unless the
__try block includes a call to the TerminateThread function). This prevents
the mutex object from being abandoned inadvertently.

BOOL FunctionToWriteToDatabase(HANDLE hMutex)
{
DWORD dwWaitResult;

// Request ownership of mutex.

dwWaitResult = WaitForSingleObject(
hMutex,   // handle to mutex
5000L);   // five-second time-out interval

switch (dwWaitResult)
{
// The thread got mutex ownership.
case WAIT_OBJECT_0:
__try {
// Write to the database.
}

__finally {
// Release ownership of the mutex object.
if (! ReleaseMutex(hMutex))
{
// Deal with error.
}

break;
}

// Cannot get mutex ownership due to time-out.
case WAIT_TIMEOUT:
return FALSE;

// Got ownership of the abandoned mutex object.
case WAIT_ABANDONED:
return FALSE;
}

return TRUE;
}

4. 学习Event

Platform SDK: DLLs, Processes, and Threads

Using Event Objects

Applications use event objects in a number of
situations to notify a waiting thread of the occurrence of an event. For
example, overlapped I/O operations on files, named pipes, and communications
devices use an event object to signal their completion. For more information
about the use of event objects in overlapped I/O operations, see Synchronization and
Overlapped Input and Output.

In the following example, an application uses event objects to prevent
several threads from reading from a shared memory buffer while a master thread
is writing to that buffer. First, the master thread uses the CreateEvent function to create a manual-reset
event object. The master thread sets the event object to nonsignaled when it is
writing to the buffer and then resets the object to signaled when it has
finished writing. Then it creates several reader threads and an auto-reset event
object for each thread. Each reader thread sets its event object to signaled
when it is not reading from the buffer.

#define NUMTHREADS 4

HANDLE hGlobalWriteEvent;
HANDLE hReadEvents[NUMTHREADS];

void CreateEventsAndThreads(void)
{
HANDLE hThread;
DWORD i, IDThread;

// Create a manual-reset event object. The master thread sets
// this to nonsignaled when it writes to the shared buffer.

hGlobalWriteEvent = CreateEvent(
NULL,         // default security attributes
TRUE,         // manual-reset event
TRUE,         // initial state is signaled
"WriteEvent"  // object name
);

if (hGlobalWriteEvent == NULL)
{
printf("CreateEvent failed (%d)/n", GetLastError());
return;
}

// Create multiple threads and an auto-reset event object
// for each thread. Each thread sets its event object to
// signaled when it is not reading from the shared buffer.

for(i = 0; i < NUMTHREADS; i++)
{
// Create the auto-reset event.
hReadEvents[i] = CreateEvent(
NULL,     // no security attributes
FALSE,    // auto-reset event
TRUE,     // initial state is signaled
NULL);    // object not named

if (hReadEvents[i] == NULL)
{
printf("CreateEvent failed (%d)/n", GetLastError());
return;
}

hThread = CreateThread(NULL, 0,
(LPTHREAD_START_ROUTINE) ThreadFunction,
&hReadEvents[i],  // pass event handle
0, &IDThread);
if (hThread == NULL)
{
printf("CreateThread failed (%d)/n", GetLastError());
return;
}
}
}

Before the master thread writes to the shared buffer, it uses the ResetEvent function to set the state of
hGlobalWriteEvent (an application-defined global variable) to nonsignaled. This
blocks the reader threads from starting a read operation. The master then uses
the WaitForMultipleObjects
function to wait for all reader threads to finish any current read operations.
When WaitForMultipleObjects returns, the master thread can safely write
to the buffer. After it has finished, it sets hGlobalWriteEvent and all the
reader-thread events to signaled, enabling the reader threads to resume their
read operations.

VOID WriteToBuffer(VOID)
{
DWORD dwWaitResult, i;

// Reset hGlobalWriteEvent to nonsignaled, to block readers.

if (! ResetEvent(hGlobalWriteEvent) )
{
printf("ResetEvent failed (%d)/n", GetLastError());
return;
}

// Wait for all reading threads to finish reading.

dwWaitResult = WaitForMultipleObjects(
NUMTHREADS,   // number of handles in array
hReadEvents,  // array of read-event handles
TRUE,         // wait until all are signaled
INFINITE);    // indefinite wait

switch (dwWaitResult)
{
// All read-event objects were signaled.
case WAIT_OBJECT_0:
// Write to the shared buffer.
break;

// An error occurred.
default:
printf("Wait error: %d/n", GetLastError());
ExitProcess(0);
}

// Set hGlobalWriteEvent to signaled.

if (! SetEvent(hGlobalWriteEvent) )
{
printf("SetEvent failed (%d)/n", GetLastError());
return;
}

// Set all read events to signaled.
for(i = 0; i < NUMTHREADS; i++)
if (! SetEvent(hReadEvents[i]) )
{
printf("SetEvent failed (%d)/n", GetLastError());
return;
}
}

Before starting a read operation, each reader thread uses WaitForMultipleObjects to wait for
the application-defined global variable hGlobalWriteEvent and its own read event
to be signaled. When WaitForMultipleObjects returns, the reader thread's
auto-reset event has been reset to nonsignaled. This blocks the master thread
from writing to the buffer until the reader thread uses the SetEvent function to set the event's state back
to signaled.

VOID ThreadFunction(LPVOID lpParam)
{
DWORD dwWaitResult;
HANDLE hEvents[2];

hEvents[0] = *(HANDLE*)lpParam;  // thread's read event
hEvents[1] = hGlobalWriteEvent;

dwWaitResult = WaitForMultipleObjects(
2,            // number of handles in array
hEvents,      // array of event handles
TRUE,         // wait till all are signaled
INFINITE);    // indefinite wait

switch (dwWaitResult)
{
// Both event objects were signaled.
case WAIT_OBJECT_0:
// Read from the shared buffer.
break;

// An error occurred.
default:
printf("Wait error: %d/n", GetLastError());
ExitThread(0);
}

// Set the read event to signaled.

if (! SetEvent(hEvents[0]) )
{
printf("SetEvent failed (%d)/n", GetLastError());
return;
}
}