为什么不从入口点函数调用 FreeLibrary？
我正在编写一个 DLL，需要多次动态调用单独的 DLL。我想保持被调用者加载，然后在卸载 DLL 时卸载它。但根据微软的说法，这是一个坏主意。
入口点函数应该只 执行简单的初始化任务 并且不应调用任何其他 DLL 加载或终止函数。为了 例如，在入口点函数中， 你不应该直接或间接 调用 LoadLibrary 函数或 LoadLibraryEx 函数。此外， 你不应该调用 FreeLibrary 当进程处于 终止。
这是有问题的代码。有人可以解释为什么我不应该从 DLL 的入口点调用 LoadLibrary 和 FreeLibrary 吗？
BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call) {
case DLL_PROCESS_DETACH :
if (hLogLib != NULL) FreeLibrary(hLogLib);
break;
}
return TRUE;
}
I'm writing a DLL that needs to call a separate DLL dynamically multiple times. I would like to keep the callee loaded and then just unload it when my DLL is unloaded. But according to Microsoft, that's a bad idea.
The entry point function should only
perform simple initialization tasks
and should not call any other DLL
loading or termination functions. For
example, in the entry point function,
you should not directly or indirectly
call the LoadLibrary function or the
LoadLibraryEx function. Additionally,
you should not call the FreeLibrary
function when the process is
terminating.
Here's the offending code. Can somebody explain why I shouldn't call LoadLibrary and FreeLibrary from my DLL's entry point?
BOOL APIENTRY DllMain( HANDLE hModule,
DWORD ul_reason_for_call,
LPVOID lpReserved
)
{
switch (ul_reason_for_call) {
case DLL_PROCESS_DETACH :
if (hLogLib != NULL) FreeLibrary(hLogLib);
break;
}
return TRUE;
}
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我想我已经找到了答案 。
I think I've found the answer.
您无法从入口点调用 LoadLibrary，因为 DllMain 函数在操作系统加载程序锁内运行，并且任何重新获取该加载程序锁的尝试（例如，通过调用 LoadLibrary）都将导致死锁。
You can't call LoadLibrary from your entry point because the DllMain function runs inside an OS loader lock and any attempts to reacquire that loader lock (for instance, by calling LoadLibrary) will result in deadlock.
不要在 DLLMain 内执行任何重要的事情。严重地。调用 FreeLibrary 更糟糕，因为如果碰巧您的 free 将引用计数减少到零并且库实际上被释放，它只会有时死锁。
Don't do anything of consequence inside of DLLMain. Seriously. Calling FreeLibrary is even worse because it'll only sometimes deadlock, if it happens that your free decrements the refcount to zero and the library is actually freed.