My dll has asynchronous function which starts a thread and returns immediately. It accepts handle of event object (type HANDLE) which the thread signals when it is done. This works fine but how can I return result from the function that it passed and no error occurred? A simple bool type will do.
I am thinking of using GetLastError() kind of call to get result of last function but I am not really sold on this way. I also looked at std::future and std::async but I am not sure if I can use that in dll function!? Another option I thought about is to use GetOverlappedResultbut that works usually with file i/o and I don't know if I can use this for a custom function that I have written.
Chad is right callback is safe and easy way to do it
// DLL:
__declspec(dllexport) void (*callback_function)(DWORD ret)=NULL;
DWORD _stdcall thread_function(LPVOID p)
{
// do something ...
if (callback_function) callback_function(some_return_value);
}
// DLL usage
DWORD return_value1=0;
bool done1=false;
void callback_function1(DWORD ret)
{
return_value1=ret;
done1=true;
}
void main()
{
callback_function=callback_function1; // set callbak function for DLL
done1=false; // invalidate return value
// here call you DLL function
for (;!done1;) Sleep(1); // wait for valid result ... also can add some timeout to avoid hang-ups
// now in return_value1 is the valid return value
}
also you can use waitforsingleobject instead
http://msdn.microsoft.com/en-us/library/windows/desktop/ms687032(v=vs.85).aspx
In my current project I need some functions exported from ntdll.dll and csrsrv.dll.
There is no problem with getting handle for ntdll and pointer to functions. But when I try get handle for csrsrv.dll function fails with error code "File not found". I've tried to specify full path to file, but it dose not change a thing.
Code for my load function from dll function:
PVOID GetFunctionFromDll(const std::string& _sModuleName,const std::string& _sFnName)
{
HMODULE hModule = NULL;
PVOID ptrFn = NULL;
if(!GetModuleHandleEx(0,_sModuleName.c_str(),&hModule))
{
return 0;
}
ptrFn = GetProcAddress(hModule, _sFnName.c_str());
FreeLibrary(hModule); // preventing handle leakage
return ptrFn;
}
Any ideas why does it fail with csrsrv.dll?
GetModuleHandleEx() does not load the DLL. From the linked reference page:
Retrieves a module handle for the specified module and increments the module's reference count unless GET_MODULE_HANDLE_EX_FLAG_UNCHANGED_REFCOUNT is specified. The module must have been loaded by the calling process.
The csrsrv.dll must not be in memory when the call is made and the ntdll.dll will be in memory, and the call succeeds.
Suggest using LoadLibrary() outside of the function to ensure the DLL remains in memory beyond the function call, guaranteeing that the address returned by GetFunctionFromDll() remains valid.
I have a wrapper class that wraps functions in an DLL. Naturally, I use LoadLibrary and FreeLibrary to load and free the DLL. When my wrapper management object gets created, it runs a Startup() function:
//at the top
#define AVTCAM_DLL_NAME (L"VimbaBridgeAPI.dll")
//startup()
void CAVTcamDllWrapper::Startup()
{
mAVTCamLibrary = LoadLibrary(AVTCAM_DLL_NAME);
if(mAVTCamLibrary == NULL)
{
//report an error
}
}
Then, when the wrapper manager gets deleted, it calls the shutdown function in its destructor:
void CAVTcamDllWrapper::Shutdown()
{
if(mAVTCamLibrary != NULL)
{
FreeLibrary(mAVTCamLibrary);
mAVTCamLibrary = NULL; //for extra safety
}
}
Here is my problem: the camera I am working with can startup just fine. The problem is during the shutdown, and more specifically, during the FreeLibrary() call. As soon as the FreeLibrary gets called, the next line of code always fails.
In this case, my debugger shows that it executed FreeLibrary and it jumps to the mAVTCamLibrary = NULL; line, then that line will result in an Access Violation Error.
If I get rid of the mAVTCamLibrary = NULL; line (which I did at first because I thought this line was causing the error), then whatever my debugger jumps to after the FreeLibrary() causes an access violation error.
I cannot figure out why I get these errors right after calling FreeLibrary(). Anyone have an idea?
In D, the main function is defined:
void main(/*perhaps some args but I do not remember*/)
{
}
I know for sure that this function returns zero on success and non-zero on failure and yet it is defined as not returning anything. What is the logic behind it?
What Alexandrescu is saying is simply shorthand for the exit code I described. The zero or nonzero returned to the OS is a (language-agnostic) process exit code, not a function return value. The OS doesn't call main directly, and main doesn't return directly to the OS. The D compiler inserts startup and shutdown code in your program to handle these interactions with the OS, as do pretty much all other compilers for other languages. On startup, for instance, this boilerplate code uses some OS-dependent mechanism to get the command-line arguments, and puts them into a D string[] array to pass to main. On shutdown, it uses the return value from int main for the exit code, or, for void main, uses its own value (0 for success, nonzero for unhandled exception).
In pseudocode:
// Generated by compiler
void _realMain()
{
// OS-dependent; probably calls GetCommandLineW
// and CommandLineToArgvW on Windows, for example
string[] cmdLineArgs = createArgArray();
int exitCode = 0; // Assume success
try
{
// static if selects only one call to main for compilation,
// depending on main's return type.
// If main has been written to return int, use its value for the exit code
static if (main returns int)
exitCode = main(cmdLineArgs);
// If main has been declared void, just run it and keep the exit code of 0
else
// void main: *doesn't return anything*
main(cmdLineArgs);
}
catch
{
// Unhandled exception results in non-zero exit code
exitCode = 1;
printStackTrace();
}
// OS-dependent process shutdown function.
// This is where the exit code is "returned" to the OS.
// Note it *does not* use the return keyword to do so.
// Calling the OS's function to kill the current process
// does not return, because the process is dead by the
// time the function has finished!
exitProcess(exitCode);
// In particular, no code *after* the exitProcess line will run.
}
There are several possible signatures for main():
void main()
void main(string[] args)
void main(char[][] args)
void main(wstring[] args)
void main(wchar[][] args)
void main(dstring[] args)
void main(dchar[][] args)
int main()
int main(string[] args)
int main(char[][] args)
int main(wstring[] args)
int main(wchar[][] args)
int main(dstring[] args)
int main(dchar[][] args)
If int is the return type, then it's pretty much the same is in C or C++. The value that you return is what the OS/shell sees. If an exception is thrown, then a stack trace is printed, and the OS/shell sees a non-zero value. I don't know what it is. It may vary by exception type.
If void is the return type, then the OS/shell sees 0. If an exception is thrown, then a stack trace is printed, and the OS sees a non-zero value. Again, I don't know what it is.
Essentially, having void main allows you to not worry about returning a value to the OS/shell. Many programs are not in the least bit concerned with returning success or failure to the OS/shell. So, with void, the OS/shell always gets 0 unless an exception is thrown - which makes sense, since the only program failure at that point is if an exception escapes main(). If you do care about returning success or failure to the OS/shell, then you simply use one of the versions that returns int.
The plethora of signatures due to different string types is that you can use pretty much any of the possible string types as the input to main(). main() and main(string[] args) are probably the most commonly used though.
function with void return type does not return any value. There is nothing illogical when you consider call stack looks like this:
OS -> D runtime -> main
The main function is invoked by D runtime system, which recognized that the main function returns nothing - and in this case return success to the OS. In case the main function is defined with return type int, then the D runtime return to OS value returned by main function.
If you define the function as
int main(...);
then the return value, that you can get (in bash) using
echo $?
will be whatever you return from the function. If you don't return anything, or you define your main function as
void main(...);
then the exit status of the command is undefined. For some reason (I can't find any documentation on this) it's always 200 on my system.
Is there any sense to step-execute release code? I noticed that some lines of code are omitted, i.e. some method calls. Also variable preview doesn't show some variables and shows invalid (not real) values for some others, so it's all quite misleading.
I'm asking this question, because loading WinDbg crashdump file into Visual Studio brings the same stack and variables partial view as step-execution. Are there any way to improve crashdump analyze experience, except recompiling application without optimalizations?
Windows, Visual Studio 2005, unmanaged C++
Yes - if you have the .pdb for the build, and the .dmp file from the crash, then you can open the debugger on the exact point of failure, and examine the state of your app at that point.
As several have noted - some variables will be optimized away, but if you're mildly creative / inquisitive, you'll find ways to obtain those values.
You can build in a root crash handler for your code to generate a .dmp file automatically which works on all Windows flavors (assuming you are creating a Windows app) using something like the following:
// capture the unhandled exception hook - we will create a mini dump for ourselves
// NOTE: according to docs, if a debugger is present, this API won't succeed (ie. debug builds ignore this)
MiniDumper::Install(
true,
filename,
"Please send a copy of this file, along with a brief description of the problem, to [insert your email address here] so that we might fix this issue."
);
The above would require the MiniDumper class I wrote, below:
#pragma once
#include <dbghelp.h>
#include "DynamicLinkLibrary.h"
#include "FileName.h"
//////////////////////////////////////////////////////////////////////////
// MiniDumper
//
// Provides a mechanism whereby an application will generate its own mini dump file anytime
// it throws an unhandled exception (or at the client's request - see GenerateMiniDump, below).
//
// Warning: the C-runtime will NOT invoke our unhandled handler if you are running a debugger
// due to the way that the SetUnhandledExceptionFilter() API works (q.v.)
//
// To use this facility, simply call MiniDumper::Install - for example, during CWinApp initialization.
//
// Once this has been installed, all current and future threads in this process will be covered.
// This is unlike the StructuredException and CRTInvalidParameter classes, which must be installed for
// for each thread for which you wish to use their services.
//
class MiniDumper
{
public:
// install the mini dumper (and optionally, hook the unhandled exception filter chain)
// #param filename is the mini dump filename to use (please include a path)
// #return success or failure
// NOTE: we can be called more than once to change our options (unhook unhandled, change the filename)
static bool Install(bool bHookUnhandledExceptionFilter, const CFilename & filenameMiniDump, const CString & strCustomizedMessage, DWORD dwMiniDumpType = MiniDumpNormal)
{
return GetSingleton().Initialize(bHookUnhandledExceptionFilter, filenameMiniDump, strCustomizedMessage, dwMiniDumpType);
}
// returns true if we've been initialized (but doesn't indicate if we have hooked the unhandled exception filter or not)
static bool IsInitialized() { return g_bInstalled; }
// returns true if we've been setup to intercept unhandled exceptions
static bool IsUnhandledExceptionHooked() { return g_bInstalled && GetSingleton().m_bHookedUnhandledExceptionFilter; }
// returns the filename we've been configured to write to if we're requested to generate a mini dump
static CFilename GetMiniDumpFilename() { return g_bInstalled ? GetSingleton().m_filenameMiniDump : ""; }
// you may use this wherever you have a valid EXCEPTION_POINTERS in order to generate a mini dump of whatever exception just occurred
// use the GetExceptionInformation() intrinsic to obtain the EXCEPTION_POINTERS in an __except(filter) context
// returns success or failure
// DO NOT hand the result of GenerateMiniDump to your __except(filter) - instead use a proper disposition value (q.v. __except)
// NOTE: you *must* have already installed MiniDumper or this will only error
static bool GenerateMiniDump(EXCEPTION_POINTERS * pExceptionPointers);
private:
// based on dbghelp.h
typedef BOOL (WINAPI * MINIDUMPWRITEDUMP_FUNC_PTR)(
HANDLE hProcess,
DWORD dwPid,
HANDLE hFile,
MINIDUMP_TYPE DumpType,
CONST PMINIDUMP_EXCEPTION_INFORMATION ExceptionParam,
CONST PMINIDUMP_USER_STREAM_INFORMATION UserStreamParam,
CONST PMINIDUMP_CALLBACK_INFORMATION CallbackParam
);
// data we need to pass to our mini dump thread
struct ExceptionThreadData
{
ExceptionThreadData(EXCEPTION_POINTERS * exceptionPointers, bool bUnhandled, DWORD threadID = ::GetCurrentThreadId())
: pExceptionPointers(exceptionPointers)
, dwThreadID(threadID)
, bUnhandledException(bUnhandled)
{
}
EXCEPTION_POINTERS * pExceptionPointers;
DWORD dwThreadID;
bool bUnhandledException;
};
// our unhandled exception filter (called automatically by the run time if we've been installed to do so)
static LONG CALLBACK UnhandledExceptionFilter(EXCEPTION_POINTERS * pExceptionPointers);
// creates a new thread in which to generate our mini dump (so we don't run out of stack)
static bool ExecuteMiniDumpThread(EXCEPTION_POINTERS * pExceptionPointers, bool bUnhandledException);
// thread entry point for generating a mini dump file
static DWORD WINAPI MiniDumpThreadProc(LPVOID lpParam);
// obtains the one and only instance
static MiniDumper & GetSingleton();
// flag to indicate if we're installed or not
static bool g_bInstalled;
// create us
MiniDumper()
: m_pPreviousFilter(NULL)
, m_pWriteMiniDumpFunction(NULL)
, m_bHookedUnhandledExceptionFilter(false)
{
}
// install our unhandled exception filter
bool Initialize(bool bHookUnhandledExceptionFilter, const CFilename & filenameMiniDump, const CString & strCustomizedMessage, DWORD dwMiniDumpType);
// generates a mini dump file
bool GenerateMiniDumpFile(ExceptionThreadData * pData);
// handle an unhandled exception
bool HandleUnhandledException(ExceptionThreadData * pData);
bool m_bHookedUnhandledExceptionFilter;
CFilename m_filenameMiniDump;
CString m_strCustomizedMessage;
DWORD m_dwMiniDumpType;
MINIDUMPWRITEDUMP_FUNC_PTR m_pWriteMiniDumpFunction;
LPTOP_LEVEL_EXCEPTION_FILTER m_pPreviousFilter;
};
And its implementation:
#include "StdAfx.h"
#include "MiniDumper.h"
using namespace Toolbox;
//////////////////////////////////////////////////////////////////////////
// Static Members
bool MiniDumper::g_bInstalled = false;
// returns true if we were able to create a mini dump for this exception
bool MiniDumper::GenerateMiniDump(EXCEPTION_POINTERS * pExceptionPointers)
{
// obtain the mini dump in a new thread context (which will have its own stack)
return ExecuteMiniDumpThread(pExceptionPointers, false);
}
// this is called from the run time if we were installed to hook the unhandled exception filter
LONG CALLBACK MiniDumper::UnhandledExceptionFilter(EXCEPTION_POINTERS * pExceptionPointers)
{
// attempt to generate the mini dump (use a separate thread to ensure this one is frozen & we have a fresh stack to work with)
ExecuteMiniDumpThread(pExceptionPointers, true);
// terminate this process, now
::TerminateProcess(GetCurrentProcess(), 0xFFFFFFFF);
// carry on as normal (we should never get here due to TerminateProcess, above)
return EXCEPTION_CONTINUE_SEARCH;
}
bool MiniDumper::ExecuteMiniDumpThread(EXCEPTION_POINTERS * pExceptionPointers, bool bUnhandledException)
{
// because this may have been created by a stack overflow
// we may be very very low on stack space
// so we'll create a new, temporary stack to work with until we fix this situation
ExceptionThreadData data(pExceptionPointers, bUnhandledException);
DWORD dwScratch;
HANDLE hMiniDumpThread = ::CreateThread(NULL, 0, MiniDumpThreadProc, &data, 0, &dwScratch);
if (hMiniDumpThread)
{
VERIFY(::WaitForSingleObject(hMiniDumpThread, INFINITE) == WAIT_OBJECT_0);
VERIFY(::GetExitCodeThread(hMiniDumpThread, &dwScratch));
VERIFY(::CloseHandle(hMiniDumpThread));
return AsBool(dwScratch);
}
return false;
}
DWORD WINAPI MiniDumper::MiniDumpThreadProc(LPVOID lpParam)
{
// retrieve our exception context from our creator
ExceptionThreadData * pData = (ExceptionThreadData *)lpParam;
// generate the actual mini dump file in this thread context - with our own stack
if (pData->bUnhandledException)
return GetSingleton().HandleUnhandledException(pData);
else
return GetSingleton().GenerateMiniDumpFile(pData);
}
bool MiniDumper::HandleUnhandledException(ExceptionThreadData * pData)
{
// generate the actual mini dump file first - hopefully we get this even if the following errors
const bool bMiniDumpSucceeded = GenerateMiniDumpFile(pData);
// try to inform the user of what's happened
CString strMessage = FString("An Unhandled Exception occurred in %s\n\nUnfortunately, this requires that the application be terminated.", CFilename::GetModuleFilename());
// create the mini dump file
if (bMiniDumpSucceeded)
{
// let user know about the mini dump
strMessage.AppendFormat("\n\nOn a higher note, we have saved some diagnostic information in %s", m_filenameMiniDump.c_str());
}
// append any custom message(s)
if (!IsEmpty(m_strCustomizedMessage))
strMessage.AppendFormat("\n\n%s", m_strCustomizedMessage);
// cap it off with an apology
strMessage.Append("\n\nThis application must be terminated now. All unsaved data will be lost. We are deeply sorry for the inconvenience.");
// let the user know that things have gone terribly wrong
::MessageBox(GetAppWindow(), strMessage, "Internal Error - Unhandled Exception", MB_ICONERROR);
// indicate success or not
return bMiniDumpSucceeded;
}
//////////////////////////////////////////////////////////////////////////
// Instance Members
MiniDumper & MiniDumper::GetSingleton()
{
static std::auto_ptr<MiniDumper> g_pSingleton(new MiniDumper);
return *g_pSingleton.get();
}
bool MiniDumper::Initialize(bool bHookUnhandledExceptionFilter, const CFilename & filenameMiniDump, const CString & strCustomizedMessage, DWORD dwMiniDumpType)
{
// check if we need to link to the the mini dump function
if (!m_pWriteMiniDumpFunction)
{
try
{
// attempt to load the debug helper DLL
DynamicLinkLibrary dll("DBGHelp.dll", true);
// get the function address we need
m_pWriteMiniDumpFunction = (MINIDUMPWRITEDUMP_FUNC_PTR)dll.GetProcAddress("MiniDumpWriteDump", false);
}
catch (CCustomException &)
{
// we failed to load the dll, or the function didn't exist
// either way, m_pWriteMiniDumpFunction will be NULL
ASSERT(m_pWriteMiniDumpFunction == NULL);
// there is nothing functional about the mini dumper if we have no mini dump function pointer
return false;
}
}
// record the filename to write our mini dumps to (NOTE: we don't do error checking on the filename provided!)
if (!IsEmpty(filenameMiniDump))
m_filenameMiniDump = filenameMiniDump;
// record the custom message to tell the user on an unhandled exception
m_strCustomizedMessage = strCustomizedMessage;
// check if they're updating the unhandled filter chain
if (bHookUnhandledExceptionFilter && !m_bHookedUnhandledExceptionFilter)
{
// we need to hook the unhandled exception filter chain
m_pPreviousFilter = ::SetUnhandledExceptionFilter(&MiniDumper::UnhandledExceptionFilter);
}
else if (!bHookUnhandledExceptionFilter && m_bHookedUnhandledExceptionFilter)
{
// we need to un-hook the unhandled exception filter chain
VERIFY(&MiniDumper::UnhandledExceptionFilter == ::SetUnhandledExceptionFilter(m_pPreviousFilter));
}
// set type of mini dump to generate
m_dwMiniDumpType = dwMiniDumpType;
// record that we've been installed
g_bInstalled = true;
// if we got here, we must have been successful
return true;
}
bool MiniDumper::GenerateMiniDumpFile(ExceptionThreadData * pData)
{
// NOTE: we don't check this before now because this allows us to generate an exception in a different thread context (rather than an exception while processing an exception in the main thread)
ASSERT(g_bInstalled);
if (!g_bInstalled)
return false;
HANDLE hFile = ::CreateFile(m_filenameMiniDump.c_str(), GENERIC_WRITE, FILE_SHARE_READ, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
if (hFile == INVALID_HANDLE_VALUE)
{
// indicate failure
return false;
}
else
{
// NOTE: don't use exception_info - its a #define!!!
Initialized<_MINIDUMP_EXCEPTION_INFORMATION> ex_info;
ex_info.ThreadId = pData->dwThreadID;
ex_info.ExceptionPointers = pData->pExceptionPointers;
// generate our mini dump
bool bStatus = FALSE != ((*m_pWriteMiniDumpFunction)(GetCurrentProcess(), GetCurrentProcessId(), hFile, (MINIDUMP_TYPE)m_dwMiniDumpType, &ex_info, NULL, NULL));
// close the mini dump file
::CloseHandle(hFile);
return bStatus;
}
}
I apologize for the fact that this is not a drop-in solution. There are dependencies on other parts of my Toolbox library. But I think it would go a long way towards giving you the right idea as to how to build-in "capture a crash mini-dump" automatically from your code, which you can then combine with your .dsp files that you can make a normal part of your development cycle - so that when a .dmp comes in - you can fire up the debugger on it with your saved .pdb from your release build (which you don't distribute!) and you can debug the crash conditions quite easily.
The above code is an amalgam of many different sources - code snippets from debugging books, from MSDN documentation, etc., etc. If I have left out attribution I mean no harm. However, I do no believe that any of the above code is significantly created by anyone but myself.
Recompile just the file of interest without optimisations :)
In general:
Switch to interleaved disassembly mode. Single-stepping through the disassembly will enable you to step into function calls that would otherwise be skipped over, and make inlined code more evident.
Look for alternative ways of getting at values in variables the debugger is not able to directly show you. If they were passed in as arguments, look up the callstack - you will often find they are visible in the caller. If they were retrieved via getters from some object, examine that object; glance over the assembly generated by the code that calculates them to work out where they were stored; etc. If all else fails and disabling optimisations / adding a printf() distorts timings sufficiently to affect debugging, add a dummy global variable and set it to the value of interest on entry to the section of interest.
At least is not a IA64 dump...
There really isn't much you can do beyond having full dump and private symbols. Modern compilers have a field day with your code and is barely recognisable, specially if you add something like LTCG.
There are two things I found usefull:
Walk up the stack until you get a good anchor on what 'this' really points to. Most times when you are in an object method frame 'this' is unreliable because of registry optmizations. Usually several calls up the stack you get an object that has the correct address and you can navigate, member reference by member reference, until your crash point and have a correct value for 'this'
uf (Windbg's unassembly function command). This little helper can list a function dissasembly in a more manageable form than the normal dissasembly view. Because it follows jumps and code re-arranges, is easier to follow the logic of uf output.
The most important thing is to have the symbol files (*.pdb). You can generate them for release builds, by default they are not active.
Then you have to know that because of optimizations, code might get re-ordered, so debugging could look a bit jerky. Also some intermediate variables might have got optimized away. Generally speaking the behaviour and visibility of data might have some restrictions.
With Visual Studio C++ 2008 you can automatically debug the *.dmp files. I believe it also works for VS 2005. For older compilers I am afraid you´ll have to use WinDbg... (Also specify of course the *.pdb files for WinDbg, otherwise the info will be quite limited)