I am running the following piece of code under the Marmalade SDK. I need to know if there's a "bug" in my code or in Marmalade:
template <class Return = void, class Param = void*>
class IFunction {
private:
static unsigned int counterId;
protected:
unsigned int id;
public:
//
static unsigned int getNewId() { return counterId++; }
template <class FunctionPointer>
static unsigned int discoverId(FunctionPointer funcPtr) {
typedef std::pair<FunctionPointer, unsigned int> FP_ID;
typedef std::vector<FP_ID> FPIDArray;
static FPIDArray siblingFunctions; // <- NOTE THIS
typename FPIDArray::iterator it = siblingFunctions.begin();
while (it != siblingFunctions.end()) {
if (funcPtr == it->first) return it->second; /// found
++it;
}
/// not found
unsigned int newId = getNewId();
siblingFunctions.push_back( FP_ID(funcPtr, newId) ); // <- NOTE THIS
return newId;
}
//
virtual ~IFunction() {}
bool operator<(const IFunction* _other) const {
if (this->id < _other->id) return true;
return false;
}
virtual Return call(Param) = 0;
};
Note that every time template class discoverId is called for the 1st time, a static local array is created.
At program exit, the Marmalade memory manager complains that the memory reserved at this line :
siblingFunctions.push_back( FP_ID(funcPtr, newId) );
hasn't been freed. (The truth is that I don't empty the array, but how could I, I don't have access to it outside that function!).
Here is the catch : Marmalade complains only for the memory reserved at the very first call of this function! This function is called several times and with several different template parameters, but the complaining always occurs only for the memory reserved at the 1st call. This is the case even if I mix up the order of the various calls to this function. Memory reserved for every call after the 1st one is automatically freed - I have checked this out.
So, who's to blame now?
I don't know what "Marmalade" is (and a quick search for this word expectedly found a lot of irrelevant references) but your code doesn't have a resource leak with respect to the static FPIDArray siblingFunctions: this object is constructed the first time the function is called. It is destroyed at some point after main() is exited. I seem to recall that the order of destruction of objects with static linkage is the reverse of order in which objects are constructed but I'm not sure if this extends function local statics.
Related
While trying to find out a problem that occurs only in a release build and not in the debug build I noticed the following behaviour (String would be invalid and would not point to anything while the int would be fine). I have given code below which gives an idea of what I was going through
typedef boost::shared_ptr<MyClass> shared_cls
typedef std::deque<shared_cls> vector_def;
typedef boost::shared_ptr<vector_def> shared_vector_def;
typedef boost::unordered_map<int,shared_vector_def> inner_map_def;
typedef boost::shared_ptr<inner_map_def> shared_inner_map_def;
static boost::unordered_map<std::string,shared_inner_map_def> bcontainer;
shared_cls& SomeMethod(const std::string& symb,const int& no)
{
shared_inner_map_def tshare = bcontainer[symb];
shared_vector_def tmp = tshare->at(no);
shared_cls t = tmp->back();
return t
}
The object MyClass looks like this
class SomeClass
{
private:
int i;
std::string s;
void set_i(int rx)
{
i = rx;
}
int get_i()
{
return i;
}
void set_s(std::string rx)
{
s = rx;
}
std::string get_s()
{
return s;
}
}
Now when I use the above method as in the following code
void main()
{
shared_cls r = SomeMethod("IBM",12);
//Here r does not have a valid string s
//However it does have a valid int i
}
Now my question is in the above main when I call the SomeMethod the r returned does not have a valid string s. It has a scrambled value I found this out by using a logger. However the value of s is totally find during the function SomeMethod. I resolved this issue by not returning the shared pointer by reference.In that case it works. Why does removing the reference make it work
Your shared_cls t goes out of scope because it is defined in the function SomeMethod itself. You need to return shared pointers by value if they are defined in the scope. In the link, it is explained why it is dangerous to return the reference of a temporary object.
In the case of std::string, string has a reference counting mechanism and when it's reference is decremented to zero, it becomes invalidated and a segmentation fault may be observed in such a case. Even if member int i is returned properly, it is still undefined behavior.
Preface:
this question is closely related to these ones: ...
- C++: Avoiding Static Initialization Order Problems and Race Conditions Simultaneously
- How to detect where a block of memory was allocated?
... but they have NO positive solution and my actual target use-case is slightly different.
During construction of the object I need to know if it is initialized in static memory bock ( BSS) or is it instantiated in Heap.
The reasons are follow:
Object by itself is designed to be initialized to "all zeros" in constructor - therefore no initialization is needed if object is statically initialized - entire block with all objects is already set to zeros when program is loaded.
Static instances of the object can be used by other statically allocated objects and alter some member variables of the object
Order of initialization of static variables is not pre-determined - i.e. my target object can be invoked before its constructor is invoked, thus altering some of its data, and constructor can be invoked later according to some unknown order of initialization of statics thus clearing already altered data. That is why I'd like to disable code in constructor for statically allocated objects.
Note: in some scenarios Object is the subject for severe multi-threaded access (it has some InterlockedIncrement/Decrement logic), and it has to be completely initialized before any thread can touch it - what i can guaranteed if i explicitly allocate it in Heep, but not in static area (but i need it for static objects too).
Sample piece of code to illustrate the case:
struct MyObject
{
long counter;
MyObject() {
if( !isStaticallyAllocated() ) {
counter = 0;
}
}
void startSomething() { InterlockedIncrement(&counter); }
void endSomething() { InterlockedDecrement(&counter); }
};
At the moment I'm trying to check if 'this' pointer in some predefined range, but this does not work reliably.
LONG_PTR STATIC_START = 0x00400000;
LONG_PTR STATIC_END = 0x02000000;
bool isStatic = (((LONG_PTR)this >= STATIC_START) && (LONG_PTR)this < STATIC_END));
Update:
sample use-case where explicit new operator is not applicable. Code is 'pseudo code', just to illustrate the use-case.
struct SyncObject() {
long counter;
SyncObject() {
if( !isStaticallyAllocated() ) {
counter = 0;
} }
void enter() { while( counter > 0 ) sleep(); counter++; }
void leave() { counter--; }
}
template <class TEnum>
struct ConstWrapper {
SyncObject syncObj;
TEnum m_value;
operator TEnum() const { return m_value; }
LPCTSTR getName() {
syncObj.enter();
if( !initialized ) {
loadNames();
intialized = true;
}
syncObj.leave();
return names[m_value];
}
}
ConstWrapper<MyEnum> MyEnumValue1(MyEnum::Value1);
You can probably achieve this by overwriting the new operator for your class. In your customized new, you can set a "magic byte" within the allocated memory, which you can later check for. This will not permit distinguishing stack from heap, but statically from dynamically allocated objects, which might be sufficient. Note, however, that in the following case
class A {
};
class B {
A a;
};
//...
B* b = new B;
b.a will be considered statically allocated with the proposed method.
Edit: A cleaner, but more complicated solution is probably a further customization of new, where you can keep track of dynamically allocated memory blocks.
Second edit: If you just want to forbid static allocation, why don't you just make the constructor private and add a factory function to the class dynamically creating the object and delivering the pointer?
class A {
private:
A () { ... }
public:
static A* Create () { return new A; }
};
I think that the best way for you to control this is to create a factory for your class. That way you have complete control of how your objects are created instead of making complicated guesses over what memory is used.
The first answer is: not portably, and it may not be possible at all on
some platforms. Under Solaris (and I think Linux as well), there is an
implicitly defined global symbol end, comparison of arbitrary
addresses works, and if this < &end (after the appropriate
conversions), the variable is static, at least as long as no dynamic
loading is involved. But this is far from general. (And it definitely
fails anytime dynamic linking is involved, regardless of the platform.)
The solution I've used in the past was to make the distinction manually.
Basically, I designed the class so that the normal constructor did the
same thing as zero initialization, and I then provided a special no-op
constructor for use with static objects:
class MayBeStatic
{
public:
enum ForStatic { isStatic };
MayBeStatic() { /* equivalent of zero initialization */ };
MayBeStatic( ForStatic ) { /* do absolutely nothing! */ };
// ...
};
When defining an instance with static lifetime, you use the second
constructor:
MayBeStatic object( MayBeStatic::isStatic );
I don't think that this is guaranteed by the standard; I think the
implementation is allowed to modify the memory any way it wants before
invoking the constructor, and in particular, I think it is allowed to
"redo" the zero initialization immediately before invoking the
constructor. None do, however, so you're probably safe in practice.
Alternatively, you can wrap all static instances in a function, so that
they are local statics, and will be initialized the first time the
function is called:
MayBeStatic&
getStaticInstance()
{
static MayBeStatic theInstance;
return theInstance;
}
Of course, you'll need a separate function for each static instance.
It looks like after thinking for a while, I've found a workable solution to identify if block is in static area or not. Let me know, please, if there are potential pitfalls.
Designed for MS Windows, which is my target platform - by another OS I actually meant another version of MS Windows: XP -> Win7. The idea is to get address space of the loaded module (.exe or .dll) and check if block is within this address space. Code which calculates start/end of static area is put into 'lib' segment thus it should be executed before all other static objects from 'user' segment, i.e. constructor can assume that staticStart/End variables are already initialized.
#include <psapi.h>
#pragma warning(push)
#pragma warning(disable: 4073)
#pragma init_seg(compiler)
#pragma warning(pop)
HANDLE gDllHandle = (HANDLE)-1;
LONG_PTR staticStart = 0;
LONG_PTR staticEnd = 0;
struct StaticAreaLocator {
StaticAreaLocator() {
if( gDllHandle == (HANDLE)-1 )
gDllHandle = GetModuleHandle(NULL);
MODULEINFO mi;
GetModuleInformation(GetCurrentProcess(), (HMODULE)gDllHandle, &mi, sizeof(mi));
staticStart = (LONG_PTR)mi.lpBaseOfDll;
staticEnd = (LONG_PTR)mi.lpBaseOfDll + mi.SizeOfImage;
// ASSERT will fail in DLL code if gDllHandle not initialized properly
LONG_PTR current_address;
#if _WIN64
ASSERT(FALSE) // to be adopted later
#else
__asm {
call _here
_here: pop eax ; eax now holds the [EIP]
mov [current_address], eax
}
#endif
ASSERT((staticStart <= current_address) && (current_address < staticEnd));
atexit(cleanup);
}
static void cleanup();
};
StaticAreaLocator* staticAreaLocator = new StaticAreaLocator();
void StaticAreaLocator::cleanup() {
delete staticAreaLocator;
staticAreaLocator = NULL;
}
I have been beating my head around this issue of static versus non-static, callback functions, function pointers, etc... My goal is to access data of a struct outside the scope of my callback interface. I am trying to do this within my class called TextDetect. I thought I was on track when I asked this question: Avoiding a static member function in c++ when using a callback interface from C
However, I still can't access the data without losing scope over the data that I am most interested. At runtime, I get "Access violation reading location ..." I'll point it out below where it fails.
I implemented the answer to my previous question as the following class, shown entirely (Note: vtrInitialize is part of a 3rd party api code int vtrInitialize(const char *inifile, vtrCallback cb, void *calldata);):
class TextDetect {
const char * inifile;
vtrImage *vtrimage;
int framecount;
public:
TextDetect();
~TextDetect();
void vtrCB(vtrTextTrack *track);
static void vtrCB_thunk(vtrTextTrack *track, void *calldata);
int vtrTest(cv::Mat);
bool DrawBox(cv::Mat&);
vtrTextTrack *texttrack;
};
TextDetect::TextDetect() : inifile("vtr.ini")
{
if (vtrInitialize(inifile, vtrCB_thunk, static_cast<void *>(this) ) == -1)
std::cout << "Error: Failure to initialize" << std::endl;
vtrimage = new vtrImage;
}
int TextDetect::vtrTest(cv::Mat imagetest)
{
/*store image data in an image structure*/
}
void TextDetect::vtrCB(vtrTextTrack *track)
{
/*send data to command line from callback */
I've tried copying the data I need a variety of ways and nothing works (this code is a continuation from above):
//texttrack = track;
//texttrack = new vtrTextTrack (*track);
memcpy(texttrack,track,sizeof(*track));
//vtrTextTrackFree(track);
}
void TextDetect::vtrCB_thunk(vtrTextTrack *track, void *calldata)
{
static_cast<TextDetect *>(calldata)->vtrCB(track);
}
This is the member function were I want the data to be used. Texttrack is public member so I might need it outside my class as well (this code is a continuation from above):
bool TextDetect::DrawBox(cv::Mat& tobeboxed)
{
And I get the access violation error at runtime here at this line of code (this code is a continuation from above):
if (texttrack->best->ocrconf > 90)
{
/*do some more stuff*/
}
}
Hopefully I'm understanding this correctly.
It seems to me that the problem is trying to copy those vtrTextTrack structs improperly.
This:
//texttrack = track;
just copies the pointer. If the owner of the struct (probably the caller of the callback function) destroys/deletes the vtrTextTrack, then you're holding on to an invalid pointer.
This one:
memcpy(texttrack,track,sizeof(*track));
will copy all the members of the vtrTextTrack, but will not copy what's being pointed to by it's member pointers (e.g. texttrack->best). Again, if the owner destroys/deletes the track, then you're holding on to invalid pointers.
And since
//texttrack = new vtrTextTrack (*track);
didn't work, I'm guessing that vtrTextTrack doesn't provide a copy constructor.
As for a workaround, first check if your third party library provides a function to copy these structs. If that's not the case (could this be by design?), then you may have to implement one yourself. This might be hard because there might be all kinds of internals that you don't know about. If you don't need the whole vtrTextTrack, I'd say define another struct and store only the information you need. Something along the lines of
SomeType* bestCopier(SomeType* src)
{
SomeType* temp;
/* copy over struct */
return temp;
}
Foo* fooCopier(Foo* src)
{
/*...*/
}
struct myTextTrack
{
public:
myTextTrack(vtrTextTrack* src)
{
//copy over stuff
m_best = bestCopier(src->best);
m_foo = fooCopier(src->foo);
}
private:
/* the members you care about*/
SomeType* m_best;
Foo * m_foo;
}
Ok so I'm wanting to write a precise 'mark and sweep' garbage collector in C++. I have hopefully made some decisions that can help me as in all my pointers will be wrapped in a 'RelocObject' and I'll have a single block of memory for the heap. This looks something like this:
// This class acts as an indirection to the actual object in memory so that it can be
// relocated in the sweep phase of garbage collector
class MemBlock
{
public:
void* Get( void ) { return m_ptr; }
private:
MemBlock( void ) : m_ptr( NULL ){}
void* m_ptr;
};
// This is of the same size as the above class and is directly cast to it, but is
// typed so that we can easily debug the underlying object
template<typename _Type_>
class TypedBlock
{
public:
_Type_* Get( void ) { return m_pObject; }
private:
TypedBlock( void ) : m_pObject( NULL ){}
// Pointer to actual object in memory
_Type_* m_pObject;
};
// This is our wrapper class that every pointer is wrapped in
template< typename _Type_ >
class RelocObject
{
public:
RelocObject( void ) : m_pRef( NULL ) {}
static RelocObject New( void )
{
RelocObject ref( (TypedBlock<_Type_>*)Allocator()->Alloc( this, sizeof(_Type_), __alignof(_Type_) ) );
new ( ref.m_pRef->Get() ) _Type_();
return ref;
}
~RelocObject(){}
_Type_* operator-> ( void ) const
{
assert( m_pRef && "ERROR! Object is null\n" );
return (_Type_*)m_pRef->Get();
}
// Equality
bool operator ==(const RelocObject& rhs) const { return m_pRef->Get() == rhs.m_pRef->Get(); }
bool operator !=(const RelocObject& rhs) const { return m_pRef->Get() != rhs.m_pRef->Get(); }
RelocObject& operator= ( const RelocObject& rhs )
{
if(this == &rhs) return *this;
m_pRef = rhs.m_pRef;
return *this;
}
private:
RelocObject( TypedBlock<_Type_>* pRef ) : m_pRef( pRef )
{
assert( m_pRef && "ERROR! Can't construct a null object\n");
}
RelocObject* operator& ( void ) { return this; }
_Type_& operator* ( void ) const { return *(_Type_*)m_pRef->Get(); }
// SS:
TypedBlock<_Type_>* m_pRef;
};
// We would use it like so...
typedef RelocObject<Impl::Foo> Foo;
void main( void )
{
Foo foo = Foo::New();
}
So in order to find the 'root' RelocObjects when I allocate in 'RelocObject::New' I pass in the 'this' pointer of the RelocObject into the allocator(garbage collector). The allocator then checks to see if the 'this' pointer is in the range of the memory block for the heap and if it is then I can assume its not a root.
So the issue comes when I want to trace from the roots through the child objects using the zero or more RelocObjects located inside each child object.
I want to find the RelocObjects in a class (ie a child object) using a 'precise' method. I could use a reflection approach and make the user Register where in each class his or her RelocObjects are. However this would be very error prone and so I'd like to do this automatically.
So instead I'm looking to use Clang to find the offsets of the RelocObjects within the classes at compile time and then load this information at program start and use this in the mark phase of the garbage collector to trace through and mark the child objects.
So my question is can Clang help? I've heard you can gather all kinds of type information during compilation using its compile time hooks. If so what should I look for in Clang ie are there any examples of doing this kind of thing?
Just to be explicit: I want to use Clang to automatically find the offset of 'Foo' (which is a typedef of RelocObject) in FooB without the user providing any 'hints' ie they just write:
class FooB
{
public:
int m_a;
Foo m_ptr;
};
Thanks in advance for any help.
Whenever a RelocObject is instantiated, it's address can be recorded in a RelocObject ownership database along with sizeof(*derivedRelocObject) which will immediately identify which Foo belongs to which FooB. You don't need Clang for that. Also since Foo will be created shortly after FooB, your ownership database system can be very simple as the order of "I've been created, here's my address and size" calls will show the owning RelocObject record directly before the RelocObject instance's that it owns.
Each RelocObject has a ownership_been_declared flag initialized as false, upon first use (which would be after the constructors have completed, since no real work should be done in the constructor), so when any of those newly created objects is first used it requests that the database update it's ownership, the database goes through it's queue of recorded addresses and can identify which objects belong to which, clear some from it's list, setting their ownership_been_declared flag to true and you will have the offsets too (if you still need them).
p.s. if you like I can share my code for an Incremental Garbage Collector I wrote many years ago, which you might find helpful.
Here is my issue.
I have a class to create timed events. It takes in:
A function pointer of void (*func)(void* arg)
A void* to the argument
A delay
The issue is I may want to create on-the-fly variables that I dont want to be a static variable in the class, or a global variable. If either of these are not met, I cant do something like:
void doStuff(void *arg)
{
somebool = *(bool*)arg;
}
void makeIt()
{
bool a = true;
container->createTimedEvent(doStuff,(void*)&a,5);
}
That wont work because the bool gets destroyed when the function returns. So I'd have to allocate these on the heap. The issue then becomes, who allocates and who deletes. what I'd like to do is to be able to take in anything, then copy its memory and manage it in the timed event class. But I dont think I can do memcpy since I dont know the tyoe.
What would be a good way to acheive this where the time event is responsible for memory managment.
Thanks
I do not use boost
class AguiTimedEvent {
void (*onEvent)(void* arg);
void* argument;
AguiWidgetBase* caller;
double timeStamp;
public:
void call() const;
bool expired() const;
AguiWidgetBase* getCaller() const;
AguiTimedEvent();
AguiTimedEvent(void(*Timefunc)(void* arg),void* arg, double timeSec, AguiWidgetBase* caller);
};
void AguiWidgetContainer::handleTimedEvents()
{
for(std::vector<AguiTimedEvent>::iterator it = timedEvents.begin(); it != timedEvents.end();)
{
if(it->expired())
{
it->call();
it = timedEvents.erase(it);
}
else
it++;
}
}
void AguiWidgetBase::createTimedEvent( void (*func)(void* data),void* data,double timeInSec )
{
if(!getWidgetContainer())
return;
getWidgetContainer()->addTimedEvent(AguiTimedEvent(func,data,timeInSec,this));
}
void AguiWidgetContainer::addTimedEvent( const AguiTimedEvent &timedEvent )
{
timedEvents.push_back(timedEvent);
}
Why would you not use boost::shared_ptr?
It offers storage duration you require since an underlying object will be destructed only when all shared_ptrs pointing to it will have been destructed.
Also it offers full thread safety.
Using C++0x unique_ptr is perfect for the job. This is a future standard, but unique_ptr is already supported under G++ and Visual Studio. For C++98 (current standard), auto_ptr works like a harder to use version of unique_ptr... For C++ TR1 (implemented in Visual Studio and G++), you can use std::tr1::shared_ptr.
Basically, you need a smart pointer. Here's how unique_ptr would work:
unique_ptr<bool> makeIt(){ // More commonly, called a "source"
bool a = true;
container->createTimedEvent(doStuff,(void*)&a,5);
return new unique_ptr<bool>(a)
}
When you use the code later...
void someFunction(){
unique_ptr<bool> stuff = makeIt();
} // stuff is deleted here, because unique_ptr deletes
// things when they leave their scope
You can also use it as a function "sink"
void sink(unique_ptr<bool> ptr){
// Use the pointer somehow
}
void somewhereElse(){
unique_ptr<bool> stuff = makeIt();
sink(stuff);
// stuff is now deleted! Stuff points to null now
}
Aside from that, you can use unique_ptr like a normal pointer, aside from the strange movement rules. There are many smart pointers, unique_ptr is just one of them. shared_ptr is implemented in both Visual Studio and G++ and is the more typical ptr. I personally like to use unique_ptr as often as possible however.
If you can't use boost or tr1, then what I'd do is write my own function that behaves like auto_ptr. In fact that's what I've done on a project here that doesn't have any boost or tr1 access. When all of the events who care about the data are done with it it automatically gets deleted.
You can just change your function definition to take in an extra parameter that represents the size of the object passed in. Then just pass the size down. So your new function declarations looks like this:
void (*func)(void* arg, size_t size)
void doStuff(void *arg, size_t size)
{
somebool = *(bool*)arg;
memcpy( arg, myStorage, size );
}
void makeIt()
{
bool a = true;
container->createTimedEvent(doStuff,(void*)&a,sizeof(bool), 5);
}
Then you can pass variables that are still on the stack and memcpy them in the timed event class. The only problem is that you don't know the type any more... but that's what happens when you cast to void*
Hope that helps.
You should re-work your class to use inheritance, not a function pointer.
class AguiEvent {
virtual void Call() = 0;
virtual ~AguiEvent() {}
};
class AguiTimedEvent {
std::auto_ptr<AguiEvent> event;
double timeSec;
AguiWidgetBase* caller;
public:
AguiTimedEvent(std::auto_ptr<AguiEvent> ev, double time, AguiWidgetBase* base)
: event(ev)
, timeSec(time)
, caller(base) {}
void call() { event->Call(); }
// All the rest of it
};
void MakeIt() {
class someclass : AguiEvent {
bool MahBool;
public:
someclass() { MahBool = false; }
void Call() {
// access to MahBool through this.
}
};
something->somefunc(AguiTimedEvent(new someclass())); // problem solved
}