94 lines
3.5 KiB
C
94 lines
3.5 KiB
C
/*++
|
|
|
|
Copyright (c) 2000 Microsoft Corporation
|
|
|
|
Module Name:
|
|
|
|
dllmain.c
|
|
|
|
Abstract:
|
|
|
|
DLL entry point. Does nothing for now. We may add to it later.
|
|
|
|
Author:
|
|
|
|
Dragos C. Sambotin (dragoss) 10-Aug-2000
|
|
|
|
--*/
|
|
|
|
// Private nt headers.
|
|
//
|
|
#include <nt.h>
|
|
#include <ntrtl.h>
|
|
#include <nturtl.h>
|
|
|
|
// Public windows headers.
|
|
//
|
|
#include <windows.h>
|
|
|
|
|
|
//+---------------------------------------------------------------------------
|
|
// DLL Entry Point
|
|
//
|
|
// DllMain should do as little work as possible. Here's why:
|
|
// 1. Incorrectly assuming that thread attach/detach are 1:1. (explain)
|
|
// 2. Performance
|
|
// a) touching pages (#3 below)
|
|
// b) assume you will be loaded by someone who is performance-critical.
|
|
//
|
|
// 1. For every process that the DLL is attached to, DllMain gets called
|
|
// with DLL_PROCESS_ATTACH. For any new threads created or destroyed
|
|
// after DLL_PROCESS_ATTACH, DllMain is called with DLL_THREAD_ATTACH
|
|
// and DLL_THREAD_DETACH events. Since it is rare that a DLL controls
|
|
// or even knows about the clients that use it, it shouldn't assume
|
|
// that DllMain is called only once (or even a small number of times).
|
|
// In fact, you should assume the worst case (that it is called a lot)
|
|
// and code for that case. This is not unrealistic either. If your
|
|
// DLL gets attached to services.exe for example, you will be hit
|
|
// with a lot of thread attach/detach events. If you don't need these
|
|
// events (and you shouldn't) your DllMain code needs to get paged in
|
|
// (assuming it's not paged in) and called.
|
|
//
|
|
// 2. Over time, people tend to lose sight of why and when DLLs are loaded.
|
|
// Further, as more APIs are added to the DLL the likelihood that the
|
|
// DLL will be loaded increases. (i.e. It becomes more useful.) It
|
|
// is your responsibility to keep the performance of your DLL at a level
|
|
// compatible with your most demanding (performance wise) client. For
|
|
// example: Say a very performance-critical client needs to use a small
|
|
// piece of functionality in your DLL. If you've done things in DllMain
|
|
// (like create heaps, or access the registry, etc.) that don't strictly
|
|
// need to be done to access that small piece of functionality, then
|
|
// it is wasteful to do so and may be the straw that broke the camel's
|
|
// back in terms of your client deciding your DLL is "too heavy" to be
|
|
// used. For the functionality in your DLL to "scale" from your first
|
|
// very simple client to the Nth performance-critical client, you've got
|
|
// to keep DllMain absolutely lean and mean.
|
|
//
|
|
// 3. Fewer code in DllMain means fewer pages touched when your DLL is
|
|
// loaded. If your DLL is loaded at all during boot of the OS or
|
|
// an application, this means faster startup times. Let's say it again
|
|
// in another way -- "the more code you add to DllMain, the slower the
|
|
// OS or application boots up". You may think now that your DLL won't
|
|
// be loaded during boot. I'll bet most of the developers of the DLLs
|
|
// that are now loaded during boot thought the same thing in the
|
|
// beginning. ;-) As your DLL becomes more useful, it gets used by
|
|
// more and more parts of the system.
|
|
//
|
|
BOOL
|
|
WINAPI
|
|
DllMain (
|
|
HINSTANCE hinst,
|
|
DWORD dwReason,
|
|
LPVOID pvReserved
|
|
)
|
|
{
|
|
if (DLL_PROCESS_ATTACH == dwReason)
|
|
{
|
|
|
|
}
|
|
else if (DLL_PROCESS_DETACH == dwReason)
|
|
{
|
|
}
|
|
return TRUE;
|
|
}
|