AsyncSemaphore to serialize Getbalances

2 files changed, 16 insertions, 8 deletions

diff --git a/TalerWallet1/Model/Model+Balances.swift b/TalerWallet1/Model/Model+Balances.swift
index 3c5c585..c5fa095 100644
--- a/TalerWallet1/Model/Model+Balances.swift
+++ b/TalerWallet1/Model/Model+Balances.swift
@@ -45,13 +45,20 @@ extension WalletModel {
     /// fetch Balances from Wallet-Core. No networking involved
     @MainActor func balancesM(_ stack: CallStack)
       async -> [Balance] {          // M for MainActor
-        do {
-            let request = Balances()
-            let response = try await sendRequest(request, ASYNCDELAY)
-            return response.balances                // trigger view update in BalancesListView
-        } catch {
-            logger.error("balancesM failed: \(error)")
-            return []
+        await semaphore.wait()
+        defer { semaphore.signal() }
+        if cachedBalances == nil {
+            do {
+                let request = Balances()
+                let response = try await sendRequest(request, ASYNCDELAY)
+                cachedBalances = response.balances
+            } catch {
+                logger.error("balancesM failed: \(error)")
+                // TODO: show error
+            }
+        } else {
+            logger.trace("returning cached Balances")
         }
+        return cachedBalances ?? []
     }
 }
diff --git a/TalerWallet1/Model/WalletModel.swift b/TalerWallet1/Model/WalletModel.swift
index 508fbf9..6a24d8e 100644
--- a/TalerWallet1/Model/WalletModel.swift
+++ b/TalerWallet1/Model/WalletModel.swift
@@ -9,13 +9,14 @@ import os.log
 fileprivate let DATABASE = "talerwalletdb-v30"
 fileprivate let ASYNCDELAY: UInt = 0   //set e.g to 6 or 9 seconds for debugging
 
-
 // MARK: -
 /// The "virtual" base class for all models
 class WalletModel: ObservableObject {
     public static let shared = WalletModel()
     static func className() -> String {"\(self)"}
     let logger = Logger (subsystem: "net.taler.gnu", category: "WalletModel")
+    let semaphore = AsyncSemaphore(value: 1)
+    var cachedBalances: [Balance]? = nil
 
     func sendRequest<T: WalletBackendFormattedRequest> (_ request: T, _ delay: UInt = 0)
       async throws -> T.Response {    // T for any Thread