I have 2 dlls: A and B.
From a code in dll A, I am loading dynamically the dll B (using dlopen on Unix and LoadLibrary on Windows). Is it guaranteed that B will be unloaded before A?
Is there any difference between Unix and Windows behavior?
There is no guarantee as to which DLL will be unloaded first (Unix and WIndows do not differ on this point).
Related
I would like to know when do we need to place a file under
C:\Windows\System32 or C:\Windows\SysWOW64, on a 64-bits windows system.
I had two DLL's, one for 32-bit, one for 64-bit.
Logically, I thought I'd place the 32-bit DLL under C:\Windows\System32, and the 64-bit DLL under C:\Windows\SysWOW64.
To my surprise, it's the other way around! The 32-bit one goes into C:\Windows\SysWOW64, and the 64-bit DLL goes into C:\Windows\System32.
Very confusing stuff. What's the reason behind this?
I believe the intent was to rename System32, but so many applications hard-coded for that path, that it wasn't feasible to remove it.
SysWoW64 wasn't intended for the dlls of 64-bit systems, it's actually something like "Windows on Windows64", meaning the bits you need to run 32bit apps on a 64bit windows.
This article explains a bit:
Windows x64 has a directory System32 that contains 64-bit DLLs (sic!).
Thus native processes with a bitness of 64 find “their” DLLs where
they expect them: in the System32 folder. A second directory,
SysWOW64, contains the 32-bit DLLs. The file system redirector does
the magic of hiding the real System32 directory for 32-bit processes
and showing SysWOW64 under the name of System32.
If you're talking about an installer, you really should not hard-code the path to the system folder. Instead, let Windows take care of it for you based on whether or not your installer is running on the emulation layer.
I should add: You should not be putting your dll's into \system32\ anyway! Modify your code, modify your installer... find a home for your bits that is NOT anywhere under c:\windows\
For example, your installer puts your dlls into:
\program files\<your app dir>\
or
\program files\common files\<your app name>\
(Note: The way you actually do this is to use the environment var: %ProgramFiles% or
%ProgramFiles(x86)% to find where Program Files is.... you do not assume it is c:\program files\ ....)
and then sets a registry tag :
HKLM\software\<your app name>
-- dllLocation
The code that uses your dlls reads the registry, then dynamically links to the dlls in that location.
The above is the smart way to go.
You do not ever install your dlls, or third party dlls into \system32\ or \syswow64. If you have to statically load, you put your dlls in your exe dir (where they will be found). If you cannot predict the exe dir (e.g. some other exe is going to call your dll), you may have to put your dll dir into the search path (avoid this if at all poss!)
system32 and syswow64 are for Windows provided files... not for anyone elses files. The only reason folks got into the bad habit of putting stuff there is because it is always in the search path, and many apps/modules use static linking. (So, if you really get down to it, the real sin is static linking -- this is a sin in native code and managed code -- always always always dynamically link!)
Ran into the same issue and researched this for a few minutes.
I was taught to use Windows 3.1 and DOS, remember those days? Shortly after I worked with Macintosh computers strictly for some time, then began to sway back to Windows after buying a x64-bit machine.
There are actual reasons behind these changes (some would say historical significance), that are necessary for programmers to continue their work.
Most of the changes are mentioned above:
Program Files vs Program Files (x86)
In the beginning the 16/86bit files were written on, '86' Intel processors.
System32 really means System64 (on 64-bit Windows)
When developers first started working with Windows7, there were several compatibility issues where other applications where stored.
SysWOW64 really means SysWOW32
Essentially, in plain english, it means 'Windows on Windows within a 64-bit machine'. Each folder is indicating where the DLLs are located for applications it they wish to use them.
Here are two links with all the basic info you need:
MSDN File System Redirector
SysWow64 Explained
Hope this clears things up!
System32 is where Windows historically placed all 32bit DLLs, and System was for the 16bit DLLs. When microsoft created the 64 bit OS, everyone I know of expected the files to reside under System64, but Microsoft decided it made more sense to put 64bit files under System32. The only reasoning I have been able to find, is that they wanted everything that was 32bit to work in a 64bit Windows w/o having to change anything in the programs -- just recompile, and it's done. The way they solved this, so that 32bit applications could still run, was to create a 32bit windows subsystem called Windows32 On Windows64. As such, the acronym SysWOW64 was created for the System directory of the 32bit subsystem. The Sys is short for System, and WOW64 is short for Windows32OnWindows64.
Since windows 16 is already segregated from Windows 32, there was no need for a Windows 16 On Windows 64 equivalence. Within the 32bit subsystem, when a program goes to use files from the system32 directory, they actually get the files from the SysWOW64 directory. But the process is flawed.
It's a horrible design. And in my experience, I had to do a lot more changes for writing 64bit applications, that simply changing the System32 directory to read System64 would have been a very small change, and one that pre-compiler directives are intended to handle.
Other folks have already done a good job of explaining this ridiculus conundrum ... and I think Chris Hoffman did an even better job here: https://www.howtogeek.com/326509/whats-the-difference-between-the-system32-and-syswow64-folders-in-windows/
My two thoughts:
We all make stupid short-sighted mistakes in life. When Microsoft named their (at the time) Win32 DLL directory "System32", it made sense at the time ... they just didn't take into consideration what would happen if/when a 64-bit (or 128-bit) version of their OS got developed later - and the massive backward compatibility issue such a directory name would cause. Hindsight is always 20-20, so I can't really blame them (too much) for such a mistake. ...HOWEVER... When Microsoft did later develop their 64-bit operating system, even with the benefit of hindsight, why oh why would they make not only the exact same short-sighted mistake AGAIN but make it even worse by PURPOSEFULLY giving it such a misleading name?!? Shame on them!!! Why not AT LEAST actually name the directory "SysWin32OnWin64" to avoid confusion?!? And what happens when they eventually produce a 128-bit OS ... then where are they going to put their 32-bit, 64-bit, and 128-bit DLLs?!?
All of this logic still seems completely flawed to me. On 32-bit versions of Windows, System32 contains 32-bit DLLs; on 64-bit versions of Windows, System32 contains 64-bit DLLs ... so that developers wouldn't have to make code changes, correct? The problem with this logic is that those developers are either now making 64-bit apps needing 64-bit DLLs or they're making 32-bit apps needing 32-bit DLLs ... either way, aren't they still screwed? I mean, if they're still making a 32-bit app, for it to now run on a 64-bit Windows, they'll now need to make a code change to find/reference the same ol' 32-bit DLL they used before (now located in SysWOW64). Or, if they're working on a 64-bit app, they're going to need to re-write their old app for the new OS anyway ... so a recompile/rebuild was going to be needed anyway!!!
Microsoft just hurts me sometimes.
I've read about running 32 bit DLLs in 64 bit environments, especially here. But I'm still getting errors. Here's what I have. I have a real old 32-bit DLL that can't be converted to 64 bit. I have another DLL, my own, written in VB.NET, that I've compiled as x86. It calls the older one. My DLL is part of a Windows Service which I've compiled to x86 as well. So all x86 running on a 64-bit Win2012 server. The older DLL is actually installed on the machine itself, not part of my DLL or the Win Svc because of the nature of that DLL.
The older DLL is invoked using the standard X = CreateObject("oldDLL"). Everything works until I try to call a method on X. Then the method can't be found.
Any thoughts?
System.Data.SQLite (SDS) is apparently the most popular way to use SQLite from a .Net application.
I was wondering if
SDS requires shipping the SQLite DLL in addition, or if SDS includes
the SQLite source code, and
SDS can be statically compiled into a
VB.Net application of it can only be shipped as a DLL?
Thank you.
To expand on my comment, SDS is a .net wrapper for unmanaged code, so you will need to ship your release code with a copy of the DLL.
As Steve mentions, there are 32 and 64bit versions of the DLL, and as i discovered after much frustration, you must have the corresponding visual c++ runtime installed on the target machine, so if you deploy the 32bit version onto a 64bit machine, it will need the 32bit c++ runtime environment installed.
An alternative that i am currently looking into but havent had time to test is csharpe-sqlite, a pure .net implementation:
http://code.google.com/p/csharp-sqlite/
Coded in c# as the name suggests, but of course usable in any .net language including vb.net
Actually it's quite easy to compile System.Data.SQLite.dll to the does not require C++ runtime. For example if you download source code and follow the build procedures you'll find statically linked (no C/C++ runtime required) copy of System.Data.SQLite.dll in the following path:
<your-src-root>\bin\<2008 or 2010>\<Win32 or x64>\ReleaseStatic
For example if your source is in C:\Work\sqlite-netFx-source-1.0.80.0 then statically linked binary for Win32 and .NET 3.5 (VS 2008) will be located in:
C:\Work\sqlite-netFx-source-1.0.80.0\bin\2008\Win32\ReleaseStatic
Furthermore since System.Data.SQLite.dll is a mixed-mode assembly consisting of a managed .netmodule and native .obj file linked together using link.exe, it is possible to build your app as a .netmodule as well and link it together with SQLite into a single mixed mode assembly.
The resulting assembly will still be either Win32 or x64, however since almost all x64 machines will have no problem running Win32 code you can just settle on Win32 as long as:
Your app is an .exe or a .dll the is always loaded into a Win32 process, and
You don't use any of x64 specific advantages such as larger address space or using unmanaged code available only in x64
I have 32bit dll files and I need to register them on windows 7 x64,
I have tries the regsvr.exe file that exists in the folder c:\windows\syswow64
However, nothing happened with me, and I haven't got a successful message.
When I searched for my dlls in regedt , I haven't found it.
So, how can I solve that.
Regards,
Aya.
It's no different to doing it on 32-bit Windows.
It also doesn't matter which of the two regsvr32.exe versions you run: The 32-bit one is clever enough to call the 64-bit one if a 64-bit DLL is passed to it, and vice versa. (At least on Windows 7.)
If you're getting an error or the registration request doesn't return at all then the problem is likely to be with the registration function in the DLL (e.g. it's getting stuck in a long or endless operation or loop due to some other platform difference), or the DLL itself (e.g. some of its dependencies are missing).
I would like to know when do we need to place a file under
C:\Windows\System32 or C:\Windows\SysWOW64, on a 64-bits windows system.
I had two DLL's, one for 32-bit, one for 64-bit.
Logically, I thought I'd place the 32-bit DLL under C:\Windows\System32, and the 64-bit DLL under C:\Windows\SysWOW64.
To my surprise, it's the other way around! The 32-bit one goes into C:\Windows\SysWOW64, and the 64-bit DLL goes into C:\Windows\System32.
Very confusing stuff. What's the reason behind this?
I believe the intent was to rename System32, but so many applications hard-coded for that path, that it wasn't feasible to remove it.
SysWoW64 wasn't intended for the dlls of 64-bit systems, it's actually something like "Windows on Windows64", meaning the bits you need to run 32bit apps on a 64bit windows.
This article explains a bit:
Windows x64 has a directory System32 that contains 64-bit DLLs (sic!).
Thus native processes with a bitness of 64 find “their” DLLs where
they expect them: in the System32 folder. A second directory,
SysWOW64, contains the 32-bit DLLs. The file system redirector does
the magic of hiding the real System32 directory for 32-bit processes
and showing SysWOW64 under the name of System32.
If you're talking about an installer, you really should not hard-code the path to the system folder. Instead, let Windows take care of it for you based on whether or not your installer is running on the emulation layer.
I should add: You should not be putting your dll's into \system32\ anyway! Modify your code, modify your installer... find a home for your bits that is NOT anywhere under c:\windows\
For example, your installer puts your dlls into:
\program files\<your app dir>\
or
\program files\common files\<your app name>\
(Note: The way you actually do this is to use the environment var: %ProgramFiles% or
%ProgramFiles(x86)% to find where Program Files is.... you do not assume it is c:\program files\ ....)
and then sets a registry tag :
HKLM\software\<your app name>
-- dllLocation
The code that uses your dlls reads the registry, then dynamically links to the dlls in that location.
The above is the smart way to go.
You do not ever install your dlls, or third party dlls into \system32\ or \syswow64. If you have to statically load, you put your dlls in your exe dir (where they will be found). If you cannot predict the exe dir (e.g. some other exe is going to call your dll), you may have to put your dll dir into the search path (avoid this if at all poss!)
system32 and syswow64 are for Windows provided files... not for anyone elses files. The only reason folks got into the bad habit of putting stuff there is because it is always in the search path, and many apps/modules use static linking. (So, if you really get down to it, the real sin is static linking -- this is a sin in native code and managed code -- always always always dynamically link!)
Ran into the same issue and researched this for a few minutes.
I was taught to use Windows 3.1 and DOS, remember those days? Shortly after I worked with Macintosh computers strictly for some time, then began to sway back to Windows after buying a x64-bit machine.
There are actual reasons behind these changes (some would say historical significance), that are necessary for programmers to continue their work.
Most of the changes are mentioned above:
Program Files vs Program Files (x86)
In the beginning the 16/86bit files were written on, '86' Intel processors.
System32 really means System64 (on 64-bit Windows)
When developers first started working with Windows7, there were several compatibility issues where other applications where stored.
SysWOW64 really means SysWOW32
Essentially, in plain english, it means 'Windows on Windows within a 64-bit machine'. Each folder is indicating where the DLLs are located for applications it they wish to use them.
Here are two links with all the basic info you need:
MSDN File System Redirector
SysWow64 Explained
Hope this clears things up!
System32 is where Windows historically placed all 32bit DLLs, and System was for the 16bit DLLs. When microsoft created the 64 bit OS, everyone I know of expected the files to reside under System64, but Microsoft decided it made more sense to put 64bit files under System32. The only reasoning I have been able to find, is that they wanted everything that was 32bit to work in a 64bit Windows w/o having to change anything in the programs -- just recompile, and it's done. The way they solved this, so that 32bit applications could still run, was to create a 32bit windows subsystem called Windows32 On Windows64. As such, the acronym SysWOW64 was created for the System directory of the 32bit subsystem. The Sys is short for System, and WOW64 is short for Windows32OnWindows64.
Since windows 16 is already segregated from Windows 32, there was no need for a Windows 16 On Windows 64 equivalence. Within the 32bit subsystem, when a program goes to use files from the system32 directory, they actually get the files from the SysWOW64 directory. But the process is flawed.
It's a horrible design. And in my experience, I had to do a lot more changes for writing 64bit applications, that simply changing the System32 directory to read System64 would have been a very small change, and one that pre-compiler directives are intended to handle.
Other folks have already done a good job of explaining this ridiculus conundrum ... and I think Chris Hoffman did an even better job here: https://www.howtogeek.com/326509/whats-the-difference-between-the-system32-and-syswow64-folders-in-windows/
My two thoughts:
We all make stupid short-sighted mistakes in life. When Microsoft named their (at the time) Win32 DLL directory "System32", it made sense at the time ... they just didn't take into consideration what would happen if/when a 64-bit (or 128-bit) version of their OS got developed later - and the massive backward compatibility issue such a directory name would cause. Hindsight is always 20-20, so I can't really blame them (too much) for such a mistake. ...HOWEVER... When Microsoft did later develop their 64-bit operating system, even with the benefit of hindsight, why oh why would they make not only the exact same short-sighted mistake AGAIN but make it even worse by PURPOSEFULLY giving it such a misleading name?!? Shame on them!!! Why not AT LEAST actually name the directory "SysWin32OnWin64" to avoid confusion?!? And what happens when they eventually produce a 128-bit OS ... then where are they going to put their 32-bit, 64-bit, and 128-bit DLLs?!?
All of this logic still seems completely flawed to me. On 32-bit versions of Windows, System32 contains 32-bit DLLs; on 64-bit versions of Windows, System32 contains 64-bit DLLs ... so that developers wouldn't have to make code changes, correct? The problem with this logic is that those developers are either now making 64-bit apps needing 64-bit DLLs or they're making 32-bit apps needing 32-bit DLLs ... either way, aren't they still screwed? I mean, if they're still making a 32-bit app, for it to now run on a 64-bit Windows, they'll now need to make a code change to find/reference the same ol' 32-bit DLL they used before (now located in SysWOW64). Or, if they're working on a 64-bit app, they're going to need to re-write their old app for the new OS anyway ... so a recompile/rebuild was going to be needed anyway!!!
Microsoft just hurts me sometimes.