Add config option 'rpcasyncthreads' to specify number of async rpc workers. Default is 1.

src/init.cpp

@@ -424,6 +424,7 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-rpcallowip=<ip>", _("Allow JSON-RPC connections from specified source. Valid for <ip> are a single IP (e.g. 1.2.3.4), a network/netmask (e.g. 1.2.3.4/255.255.255.0) or a network/CIDR (e.g. 1.2.3.4/24). This option can be specified multiple times"));
     strUsage += HelpMessageOpt("-rpcthreads=<n>", strprintf(_("Set the number of threads to service RPC calls (default: %d)"), 4));
     strUsage += HelpMessageOpt("-rpckeepalive", strprintf(_("RPC support for HTTP persistent connections (default: %d)"), 1));
+    strUsage += HelpMessageOpt("-rpcasyncthreads=<n>", strprintf(_("Set the number of threads to service Async RPC calls (default: %d)"), 1));
 
     strUsage += HelpMessageGroup(_("RPC SSL options: (see the Bitcoin Wiki for SSL setup instructions)"));
     strUsage += HelpMessageOpt("-rpcssl", _("Use OpenSSL (https) for JSON-RPC connections"));

src/rpcserver.cpp

@@ -746,9 +746,16 @@ void StartRPCThreads()
 
     // Launch at least one async rpc worker
     async_rpc_queue = std::make_shared<AsyncRPCQueue>();
-    async_rpc_queue->addWorker();
-    async_rpc_queue->addWorker();
-    async_rpc_queue->addWorker();
+    int n = GetArg("-rpcasyncthreads", 1);
+    if (n<1) {
+        LogPrintf("ERROR: Invalid value %d for -rpcasyncthreads.  Must be at least 1.\n", n);
+        strerr = strprintf(_("An error occurred while setting up the Async RPC threads, invalid parameter value of %d (must be at least 1)."), n);
+        uiInterface.ThreadSafeMessageBox(strerr, "", CClientUIInterface::MSG_ERROR);
+        StartShutdown();
+        return;
+    }
+    for (int i = 0; i < n; i++)
+        async_rpc_queue->addWorker();
 
 }