[wallet] setup wallet background flushing in WalletInit directly

WalletInit::Start calls postInitProcess() for each wallet. Previously
each call to postInitProcess() would attempt to schedule wallet
background flushing.

Just start wallet background flushing once from WalletInit::Start().

src/wallet/init.cpp

@@ -6,6 +6,7 @@
 #include <chainparams.h>
 #include <init.h>
 #include <net.h>
+#include <scheduler.h>
 #include <util.h>
 #include <utilmoneystr.h>
 #include <validation.h>
@@ -264,8 +265,11 @@ bool WalletInit::Open() const
 void WalletInit::Start(CScheduler& scheduler) const
 {
     for (CWallet* pwallet : GetWallets()) {
-        pwallet->postInitProcess(scheduler);
+        pwallet->postInitProcess();
     }
+
+    // Run a thread to flush wallet periodically
+    scheduler.scheduleEvery(MaybeCompactWalletDB, 500);
 }
 
 void WalletInit::Flush() const

src/wallet/wallet.cpp

@@ -23,7 +23,6 @@
 #include <primitives/block.h>
 #include <primitives/transaction.h>
 #include <script/script.h>
-#include <scheduler.h>
 #include <timedata.h>
 #include <txmempool.h>
 #include <utilmoneystr.h>
@@ -4308,18 +4307,11 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
     return walletInstance;
 }
 
-std::atomic<bool> CWallet::fFlushScheduled(false);
-
-void CWallet::postInitProcess(CScheduler& scheduler)
+void CWallet::postInitProcess()
 {
     // Add wallet transactions that aren't already in a block to mempool
     // Do this here as mempool requires genesis block to be loaded
     ReacceptWalletTransactions();
-
-    // Run a thread to flush wallet periodically
-    if (!CWallet::fFlushScheduled.exchange(true)) {
-        scheduler.scheduleEvery(MaybeCompactWalletDB, 500);
-    }
 }
 
 bool CWallet::BackupWallet(const std::string& strDest)

src/wallet/wallet.h

@@ -68,7 +68,6 @@ class CCoinControl;
 class COutput;
 class CReserveKey;
 class CScript;
-class CScheduler;
 class CTxMemPool;
 class CBlockPolicyEstimator;
 class CWalletTx;
@@ -675,7 +674,6 @@ class WalletRescanReserver; //forward declarations for ScanForWalletTransactions
 class CWallet final : public CCryptoKeyStore, public CValidationInterface
 {
 private:
-    static std::atomic<bool> fFlushScheduled;
     std::atomic<bool> fAbortRescan{false};
     std::atomic<bool> fScanningWallet{false}; // controlled by WalletRescanReserver
     std::mutex mutexScanning;
@@ -1127,7 +1125,7 @@ public:
      * Wallet post-init setup
      * Gives the wallet a chance to register repetitive tasks and complete post-init tasks
      */
-    void postInitProcess(CScheduler& scheduler);
+    void postInitProcess();
 
     bool BackupWallet(const std::string& strDest);