rpc: increase the defaults for -rpcthreads and -rpcworkqueue

`rpcthreads` was introduced with a default of 4 in 2013 in
21eb5ad

`rpcworkqueue` was introduced with a default of 16 in 2015 in
40b556d

Resolves: bitcoin#29386

src/httpserver.h

@@ -14,8 +14,17 @@ namespace util {
 class SignalInterrupt;
 } // namespace util
 
-static const int DEFAULT_HTTP_THREADS=4;
-static const int DEFAULT_HTTP_WORKQUEUE=16;
+/**
+ * The default value for `-rpcthreads`. This number of threads will be created at startup.
+ */
+static const int DEFAULT_HTTP_THREADS=16;
+
+/**
+ * The default value for `-rpcworkqueue`. This is the maximum depth of the work queue,
+ * we don't allocate this number of work queue items upfront.
+ */
+static const int DEFAULT_HTTP_WORKQUEUE=64;
+
 static const int DEFAULT_HTTP_SERVER_TIMEOUT=30;
 
 struct evhttp_request;

src/init.cpp

@@ -664,7 +664,7 @@ void SetupServerArgs(ArgsManager& argsman, bool can_listen_ipc)
     argsman.AddArg("-rpcuser=<user>", "Username for JSON-RPC connections", ArgsManager::ALLOW_ANY | ArgsManager::SENSITIVE, OptionsCategory::RPC);
     argsman.AddArg("-rpcwhitelist=<whitelist>", "Set a whitelist to filter incoming RPC calls for a specific user. The field <whitelist> comes in the format: <USERNAME>:<rpc 1>,<rpc 2>,...,<rpc n>. If multiple whitelists are set for a given user, they are set-intersected. See -rpcwhitelistdefault documentation for information on default whitelist behavior.", ArgsManager::ALLOW_ANY, OptionsCategory::RPC);
     argsman.AddArg("-rpcwhitelistdefault", "Sets default behavior for rpc whitelisting. Unless rpcwhitelistdefault is set to 0, if any -rpcwhitelist is set, the rpc server acts as if all rpc users are subject to empty-unless-otherwise-specified whitelists. If rpcwhitelistdefault is set to 1 and no -rpcwhitelist is set, rpc server acts as if all rpc users are subject to empty whitelists.", ArgsManager::ALLOW_ANY, OptionsCategory::RPC);
-    argsman.AddArg("-rpcworkqueue=<n>", strprintf("Set the depth of the work queue to service RPC calls (default: %d)", DEFAULT_HTTP_WORKQUEUE), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::RPC);
+    argsman.AddArg("-rpcworkqueue=<n>", strprintf("Set the maximum depth of the work queue to service RPC calls (default: %d)", DEFAULT_HTTP_WORKQUEUE), ArgsManager::ALLOW_ANY | ArgsManager::DEBUG_ONLY, OptionsCategory::RPC);
     argsman.AddArg("-server", "Accept command line and JSON-RPC commands", ArgsManager::ALLOW_ANY, OptionsCategory::RPC);
     if (can_listen_ipc) {
         argsman.AddArg("-ipcbind=<address>", "Bind to Unix socket address and listen for incoming connections. Valid address values are \"unix\" to listen on the default path, <datadir>/node.sock, or \"unix:/custom/path\" to specify a custom path. Can be specified multiple times to listen on multiple paths. Default behavior is not to listen on any path. If relative paths are specified, they are interpreted relative to the network data directory. If paths include any parent directory components and the parent directories do not exist, they will be created.", ArgsManager::ALLOW_ANY, OptionsCategory::IPC);