what is a loader lock?

by

For example, review this question:

Loader lock error

The general idea of loader lock: The system runs the code in DllMain inside a lock (as in – synchronization lock). Therefore, running non-trivial code inside DllMain is “asking for a deadlock”

Answer I’ve mentioned is based on this article:

Another reason not to do anything scary in your DllMain: Inadvertent deadlock

Your DllMain function runs inside the loader lock, one of the few times the OS lets you run code while one of its internal locks is held. This means that you must be extra careful not to violate a lock hierarchy in your DllMain; otherwise, you are asking for a deadlock.

The loader lock is taken by any function that needs to access the list of DLLs loaded into the process. This includes functions like GetModuleHandle and GetModuleFileName. If your DllMain enters a critical section or waits on a synchronization object, and that critical section or synchronization object is owned by some code that is in turn waiting for the loader lock, you just created a deadlock:

// global variable
CRITICAL_SECTION g_csGlobal;

// some code somewhere
EnterCriticalSection(&g_csGlobal);
... GetModuleFileName(MyInstance, ..);
LeaveCriticalSection(&g_csGlobal);

BOOL WINAPI
DllMain(HINSTANCE hinstDLL, DWORD fdwReason,
        LPVOID lpvReserved)
{
  switch (fdwReason) {
  ...
  case DLL_THREAD_DETACH:
   EnterCriticalSection(&g_csGlobal);
   ...
  }
  ...
}

Please review the whole article for full understanding.

More Related Contents:

  1. Recursive Lock (Mutex) vs Non-Recursive Lock (Mutex)
  2. Re-entrant locks in C#
  3. What’s the maximum number of threads in Windows Server 2003?
  4. What is a deadlock?
  5. What is the difference between mutex and critical section?
  6. Command-line tool for finding out who is locking a file
  7. Enumerating threads in Windows
  8. Accessing a single file with multiple threads
  9. VB – Linking a DLL in implicit way
  10. OpenSSL and multi-threads
  11. ReentrantReadWriteLock: what’s the difference between ReadLock and WriteLock?
  12. How to delete subfolders and Files but not parent Folder in windows using Script? [closed]
  13. How does the Windows Command Interpreter (CMD.EXE) parse scripts?
  14. What is the Windows version of cron? [closed]
  15. Git – How to use .netrc file on Windows to save user and password
  16. The difference between the ‘Local System’ account and the ‘Network Service’ account?
  17. Running PowerShell in Task Scheduler
  18. SVN repository backup strategies
  19. XCOPY still asking (F = file, D = directory) confirmation
  20. How can we check if a file Exists or not using Win32 program?
  21. Redirecting Output from within Batch file
  22. Changing .gitconfig location on Windows
  23. Monitor vs lock
  24. What is the Windows equivalent of process.on(‘SIGINT’) in node.js?
  25. How to use clang with mingw-w64 headers on windows
  26. How to wait for a process to terminate to execute another process in batch file
  27. Anything like dos2unix for Windows?
  28. Cannot read unicode .csv into R
  29. Cross-Process Locking in C#
  30. Alternative to Win32_Product?

Leave a Comment