Merge bitcoin/bitcoin#25067: validationinterface: make MainSignalsInstance() a class, drop unused forward declarations

ca1ac1f scripted-diff: Rename MainSignalsInstance() class to MainSignalsImpl() (Jon Atack)
2aaec23 refactor: remove unused forward declarations in validationinterface.h (Jon Atack)
23854f8 refactor: make MainSignalsInstance() a class (Jon Atack)

Pull request description:

  Make MainSignalsInstance a class, rename it to MainSignalsImpl, use Doxygen documentation for it, and remove no longer used forward declarations in src/validationinterface.h.

  ----

  MainSignalsInstance was created in 3a19fed and originally was a collection of boost::signals methods moved to validationinterface.cpp, in order to no longer need to include boost/signals in validationinterface.h.

  MainSignalsInstance then evolved in d6815a2 to become class-like:

  - [C.8: Use class rather than struct if any member is non-public](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-class)

   - [C.2: Use class if the class has an invariant; use struct if the data members can vary independently](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#c2-use-class-if-the-class-has-an-invariant-use-struct-if-the-data-members-can-vary-independently)

  - A class has the advantage of default private access, as opposed to public for a struct.

ACKs for top commit:
  furszy:
    Code ACK ca1ac1f
  promag:
    Code review ACK ca1ac1f.
  danielabrozzoni:
    Code review ACK ca1ac1f

Tree-SHA512: 25f85e2b582fe8c269e6cf384a4aa29350b97ea6477edf3c63591e4f68a97364f7fb2fc4ad2764f61ff86b27353e31d2f12eed7a23368a247e4cf271c7e133ea

Author: MacroFake

src/validationinterface.cpp

@@ -16,14 +16,16 @@
 #include <unordered_map>
 #include <utility>
 
-//! The MainSignalsInstance manages a list of shared_ptr<CValidationInterface>
-//! callbacks.
-//!
-//! A std::unordered_map is used to track what callbacks are currently
-//! registered, and a std::list is to used to store the callbacks that are
-//! currently registered as well as any callbacks that are just unregistered
-//! and about to be deleted when they are done executing.
-struct MainSignalsInstance {
+/**
+ * MainSignalsImpl manages a list of shared_ptr<CValidationInterface> callbacks.
+ *
+ * A std::unordered_map is used to track what callbacks are currently
+ * registered, and a std::list is used to store the callbacks that are
+ * currently registered as well as any callbacks that are just unregistered
+ * and about to be deleted when they are done executing.
+ */
+class MainSignalsImpl
+{
 private:
     Mutex m_mutex;
     //! List entries consist of a callback pointer and reference count. The
@@ -40,7 +42,7 @@ struct MainSignalsInstance {
     // our own queue here :(
     SingleThreadedSchedulerClient m_schedulerClient;
 
-    explicit MainSignalsInstance(CScheduler& scheduler LIFETIMEBOUND) : m_schedulerClient(scheduler) {}
+    explicit MainSignalsImpl(CScheduler& scheduler LIFETIMEBOUND) : m_schedulerClient(scheduler) {}
 
     void Register(std::shared_ptr<CValidationInterface> callbacks)
     {
@@ -92,7 +94,7 @@ static CMainSignals g_signals;
 void CMainSignals::RegisterBackgroundSignalScheduler(CScheduler& scheduler)
 {
     assert(!m_internals);
-    m_internals = std::make_unique<MainSignalsInstance>(scheduler);
+    m_internals = std::make_unique<MainSignalsImpl>(scheduler);
 }
 
 void CMainSignals::UnregisterBackgroundSignalScheduler()

src/validationinterface.h

@@ -17,9 +17,7 @@ class BlockValidationState;
 class CBlock;
 class CBlockIndex;
 struct CBlockLocator;
-class CConnman;
 class CValidationInterface;
-class uint256;
 class CScheduler;
 enum class MemPoolRemovalReason;
 
@@ -177,10 +175,10 @@ class CValidationInterface {
     friend class ValidationInterfaceTest;
 };
 
-struct MainSignalsInstance;
+class MainSignalsImpl;
 class CMainSignals {
 private:
-    std::unique_ptr<MainSignalsInstance> m_internals;
+    std::unique_ptr<MainSignalsImpl> m_internals;
 
     friend void ::RegisterSharedValidationInterface(std::shared_ptr<CValidationInterface>);
     friend void ::UnregisterValidationInterface(CValidationInterface*);