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// *****************************************************************************
// * This file is part of the FreeFileSync project. It is distributed under *
// * GNU General Public License: https://www.gnu.org/licenses/gpl-3.0 *
// * Copyright (C) Zenju (zenju AT freefilesync DOT org) - All Rights Reserved *
// *****************************************************************************
#ifndef GLOBALS_H_8013740213748021573485
#define GLOBALS_H_8013740213748021573485
#include <atomic>
#include <memory>
#include "scope_guard.h"
namespace zen
{
/*
Solve static destruction order fiasco by providing shared ownership and serialized access to global variables
=>there may be accesses to "Global<T>::get()" during process shutdown e.g. _("") used by message in debug_minidump.cpp or by some detached thread assembling an error message!
=> use trivially-destructible POD only!!!
ATTENTION: function-static globals have the compiler generate "magic statics" == compiler-genenerated locking code which will crash or leak memory when accessed after global is "dead"
=> "solved" by FunStatGlobal, but we can't have "too many" of these...
*/
template <class T>
class Global //don't use for function-scope statics!
{
public:
Global()
{
static_assert(std::is_trivially_constructible_v<Pod>&& std::is_trivially_destructible_v<Pod>, "this memory needs to live forever");
assert(!pod_.inst && !pod_.spinLock); //we depend on static zero-initialization!
}
explicit Global(std::unique_ptr<T>&& newInst) { set(std::move(newInst)); }
~Global() { set(nullptr); }
std::shared_ptr<T> get() //=> return std::shared_ptr to let instance life time be handled by caller (MT usage!)
{
while (pod_.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
if (pod_.inst)
return *pod_.inst;
return nullptr;
}
void set(std::unique_ptr<T>&& newInst)
{
std::shared_ptr<T>* tmpInst = nullptr;
if (newInst)
tmpInst = new std::shared_ptr<T>(std::move(newInst));
{
while (pod_.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
std::swap(pod_.inst, tmpInst);
}
delete tmpInst;
}
private:
struct Pod
{
std::atomic<bool> spinLock; // { false }; rely entirely on static zero-initialization! => avoid potential contention with worker thread during Global<> construction!
//serialize access; can't use std::mutex: has non-trival destructor
std::shared_ptr<T>* inst; // = nullptr;
} pod_;
};
//===================================================================================================================
//===================================================================================================================
struct CleanUpEntry
{
using CleanUpFunction = void (*)(void* callbackData);
CleanUpFunction cleanUpFun;
void* callbackData;
CleanUpEntry* prev;
};
void registerGlobalForDestruction(CleanUpEntry& entry);
template <class T>
class FunStatGlobal
{
public:
//No FunStatGlobal() or ~FunStatGlobal()!
std::shared_ptr<T> get()
{
static_assert(std::is_trivially_constructible_v<FunStatGlobal>&&
std::is_trivially_destructible_v<FunStatGlobal>, "this class must not generate code for magic statics!");
while (pod_.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
if (pod_.inst)
return *pod_.inst;
return nullptr;
}
void set(std::unique_ptr<T>&& newInst)
{
std::shared_ptr<T>* tmpInst = nullptr;
if (newInst)
tmpInst = new std::shared_ptr<T>(std::move(newInst));
{
while (pod_.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
std::swap(pod_.inst, tmpInst);
registerDestruction();
}
delete tmpInst;
}
void initOnce(std::unique_ptr<T> (*getInitialValue)())
{
while (pod_.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(pod_.spinLock = false);
if (!pod_.cleanUpEntry.cleanUpFun)
{
assert(!pod_.inst);
if (std::unique_ptr<T> newInst = (*getInitialValue)())
pod_.inst = new std::shared_ptr<T>(std::move(newInst));
registerDestruction();
}
}
private:
//call while holding pod_.spinLock
void registerDestruction()
{
assert(pod_.spinLock);
if (!pod_.cleanUpEntry.cleanUpFun)
{
pod_.cleanUpEntry.callbackData = this;
pod_.cleanUpEntry.cleanUpFun = [](void* callbackData)
{
auto thisPtr = static_cast<FunStatGlobal*>(callbackData);
thisPtr->set(nullptr);
};
registerGlobalForDestruction(pod_.cleanUpEntry);
}
}
struct Pod
{
std::atomic<bool> spinLock; // { false }; rely entirely on static zero-initialization! => avoid potential contention with worker thread during Global<> construction!
//serialize access; can't use std::mutex: has non-trival destructor
std::shared_ptr<T>* inst; // = nullptr;
CleanUpEntry cleanUpEntry;
} pod_;
};
inline
void registerGlobalForDestruction(CleanUpEntry& entry)
{
static struct
{
std::atomic<bool> spinLock;
CleanUpEntry* head;
} cleanUpList;
static_assert(std::is_trivially_constructible_v<decltype(cleanUpList)>&&
std::is_trivially_destructible_v<decltype(cleanUpList)>, "we must not generate code for magic statics!");
while (cleanUpList.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(cleanUpList.spinLock = false);
std::atexit([]
{
while (cleanUpList.spinLock.exchange(true)) ;
ZEN_ON_SCOPE_EXIT(cleanUpList.spinLock = false);
(*cleanUpList.head->cleanUpFun)(cleanUpList.head->callbackData);
cleanUpList.head = cleanUpList.head->prev; //nicely clean up in reverse order of construction
});
entry.prev = cleanUpList.head;
cleanUpList.head = &entry;
}
}
#endif //GLOBALS_H_8013740213748021573485
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