Merge #17993: gui: Balance/TxStatus polling update based on last block hash.

a06e845e826acaeb0db7cf02b2519c177e94dee5 BlockTip struct created and connected to notifyHeaderTip and notifyBlockTip signals. (furszy)
2f867203b0c7a4438ce484be4cfa2b29dbf1abf0 Added best block hash to the NotifyHeaderTip and NotifyBlockTip signals. (furszy)

Pull request description:

  Rationale:

  The height based polling in the GUI is an issue on chain reorgs. Any new tip signal with the same height as the one that it's cached in the model was not triggering the GUI update (interpreting it as the same same block when it could receive a different one). Ending up with bad information presented in the GUI.

  This PR essentially changes the last cached height to be a last cached block hash.

  ---

  Old historical information of this PR.

  As the tip height is cached and updated via signaling in clientModel, there is no need to continue locking `cs_main` on every balance poll (`m_node.getNumBlocks()` method call).

  Extra topic:

  Would suggest to change the `cachedNumBlocks` field inside `walletModel` to a more understandable name, maybe `nLastBalanceUpdateHeight`.

  And finally, this will have the equal height reorg issue mentioned [here](https://github.com/bitcoin/bitcoin/pull/17905#issuecomment-577324304), whatever is presented to fix it, this should use the same flow too.

  **[Edit - 24/01/2020]**

  Have added #[17905](https://github.com/bitcoin/bitcoin/pull/17905#issuecomment-577324304) comment fix here too.

ACKs for top commit:
  jonasschnelli:
    utACK a06e845e826acaeb0db7cf02b2519c177e94dee5 - it would be great to have QT unit tests  (in this case for a reorg) that either automatically inspect the window content based on accessibility and tests for expected values or at least allow for quick manual re-testing (screenshots, automatically create UI situations).
  hebasto:
    re-ACK a06e845e826acaeb0db7cf02b2519c177e94dee5, suggested style changes implemented since the [previous](https://github.com/bitcoin/bitcoin/pull/17993#pullrequestreview-417249705) review.
  ryanofsky:
    Code review ACK a06e845e826acaeb0db7cf02b2519c177e94dee5. A lot of changes since the last review: rebase after sync_state introduction #18152 and tryGetBalances revert #18587, reverting getLastBlockTime change, fixing spacing and initializations and renaming some variables

Tree-SHA512: 835e587a8296df9899cccd7b3e598a5970942b640e432e6a32de0b4eaea5b40f9271258f089ec033595311707b74a0f7187ecf8ed397c713e1153e2714072975

1 files changed, 4 insertions, 2 deletions

diff --git a/src/qt/walletmodel.h b/src/qt/walletmodel.h
index 7bd6d9cde0..38e8a14556 100644
--- a/src/qt/walletmodel.h
+++ b/src/qt/walletmodel.h
@@ -144,8 +144,8 @@ public:
 
     interfaces::Node& node() const { return m_node; }
     interfaces::Wallet& wallet() const { return *m_wallet; }
+    ClientModel& clientModel() const { return *m_client_model; }
     void setClientModel(ClientModel* client_model);
-    int getNumBlocks() const { return cachedNumBlocks; }
 
     QString getWalletName() const;
     QString getDisplayName() const;
@@ -181,9 +181,11 @@ private:
     // Cache some values to be able to detect changes
     interfaces::WalletBalances m_cached_balances;
     EncryptionStatus cachedEncryptionStatus;
-    int cachedNumBlocks;
     QTimer* timer;
 
+    // Block hash denoting when the last balance update was done.
+    uint256 m_cached_last_update_tip{};
+
     void subscribeToCoreSignals();
     void unsubscribeFromCoreSignals();
     void checkBalanceChanged(const interfaces::WalletBalances& new_balances);