Re: DllMain entrypoint - Is it serialized?
I want to write a DLL with shared memory. I thought I could
initialize the required synchronization resources in DllMain after
reading the following documentation:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllp...
"Access to the entry point is serialized by the system on a
process-wide basis. Threads in DllMain hold the loader lock so no
additional DLLs can be dynamically loaded or initialized."
I decided to do a simple test. I wrote a small DLL with a debug print
message followed by a Sleep(10000) in DllMain when a process attached
to the DLL (case "DLL_PROCESS_ATTACH"). Now I linked the DLL with two
programs and executed them at about the same time.
To my surprise, when one process printed and was still sleeping, the
other process also printed the debug message. Does this mean that both
the processes were in DllMain of my DLL at the same time? What am I
missing here?
If your dll is loaded by 2 processes, the functions in your dll (including
the dllmain function) are executed independently.
The synchronization is per process.
And even then, there are a few undocumented quirks where some cases are
serialized, and others are not.
To be safe, you musn't ever do anything inside dllmain that causes the
loading or unloading of another dll.
if you want to protect your shared memory, I suspect your critical section
objects are named.
In that case, I hope your dll is not going to be used on Windows 2000,
because initializing named objects on win2000 can cause the loading of a
dll, which can cause a deadlock. This is documented in msdn.
In that case you have to provide explicit functions for initialization, or
perform a check in all exported functions to see if initialization still
needs to be done or not.
--
Kind regards,
Bruno van Dooren
bruno_nos_pam_van_dooren@hotmail.com
Remove only "_nos_pam"