From e47fdfb5d79a32075ec10f5549c07a2e8310079f Mon Sep 17 00:00:00 2001
From: "William A. Kennington III" <wak@google.com>
Date: Thu, 15 Mar 2018 17:09:28 -0700
Subject: utils: Add a class to cache service lookups

Currently we are doing interface + path -> service lookups for each ipmi
command sent to the daemon. For many types of commands this is not ideal
as the daemon is unlikely to change often at runtime. Implement a basic
cache with the ability to invalidate the service name at any time. This
is used by code in a future commit.

Change-Id: I85b04dd17ac19e31d49070f289704b429bd1e577
Signed-off-by: William A. Kennington III <wak@google.com>
---
 utils.cpp | 41 +++++++++++++++++++++++++++++++++++++++++
 utils.hpp | 61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 101 insertions(+), 1 deletion(-)

diff --git a/utils.cpp b/utils.cpp
index bd8fade..31c219c 100644
--- a/utils.cpp
+++ b/utils.cpp
@@ -250,6 +250,47 @@ void setDbusProperty(sdbusplus::bus::bus& bus,
 }
 
 
+ServiceCache::ServiceCache(const std::string& intf, const std::string& path)
+    : intf(intf), path(path), cachedService(std::experimental::nullopt),
+      cachedBusName(std::experimental::nullopt)
+{
+}
+
+ServiceCache::ServiceCache(std::string&& intf, std::string&& path)
+    : intf(std::move(intf)), path(std::move(path)),
+      cachedService(std::experimental::nullopt),
+      cachedBusName(std::experimental::nullopt)
+{
+}
+
+const std::string& ServiceCache::getService(sdbusplus::bus::bus& bus)
+{
+    if (!isValid(bus))
+    {
+        cachedBusName = bus.get_unique_name();
+        cachedService = ::ipmi::getService(bus, intf, path);
+    }
+    return cachedService.value();
+}
+
+void ServiceCache::invalidate()
+{
+    cachedBusName = std::experimental::nullopt;
+    cachedService = std::experimental::nullopt;
+}
+
+sdbusplus::message::message ServiceCache::newMethodCall(
+        sdbusplus::bus::bus& bus, const char *intf, const char *method)
+{
+    return bus.new_method_call(getService(bus).c_str(), path.c_str(),
+                               intf, method);
+}
+
+bool ServiceCache::isValid(sdbusplus::bus::bus& bus) const
+{
+    return cachedService && cachedBusName == bus.get_unique_name();
+}
+
 std::string getService(sdbusplus::bus::bus& bus,
                        const std::string& intf,
                        const std::string& path)
diff --git a/utils.hpp b/utils.hpp
index b4f090f..878b05a 100644
--- a/utils.hpp
+++ b/utils.hpp
@@ -1,7 +1,8 @@
 #pragma once
+#include <experimental/optional>
+#include <sdbusplus/server.hpp>
 
 #include "types.hpp"
-#include <sdbusplus/server.hpp>
 
 namespace ipmi
 {
@@ -20,6 +21,64 @@ constexpr auto METHOD_GET = "Get";
 constexpr auto METHOD_GET_ALL = "GetAll";
 constexpr auto METHOD_SET = "Set";
 
+/** @class ServiceCache
+ *  @brief Caches lookups of service names from the object mapper.
+ *  @details Most ipmi commands need to talk to other dbus daemons to perform
+ *           their intended actions on the BMC. This usually means they will
+ *           first look up the service name providing the interface they
+ *           require. This class reduces the number of such calls by caching
+ *           the lookup for a specific service.
+ */
+class ServiceCache {
+    public:
+        /** @brief Creates a new service cache for the given interface
+         *         and path.
+         *
+         *  @param[in] intf - The interface used for each lookup
+         *  @param[in] path - The path used for each lookup
+         */
+        ServiceCache(const std::string& intf, const std::string& path);
+        ServiceCache(std::string&& intf, std::string&& path);
+
+        /** @brief Gets the service name from the cache or does in a
+         *         lookup when invalid.
+         *
+         *  @param[in] bus - The bus associated with and used for looking
+         *                   up the service.
+         */
+        const std::string& getService(sdbusplus::bus::bus& bus);
+
+        /** @brief Invalidates the current service name */
+        void invalidate();
+
+        /** @brief A wrapper around sdbusplus bus.new_method_call
+         *
+         *  @param[in] bus - The bus used for calling the method
+         *  @param[in] intf - The interface containing the method
+         *  @param[in] method - The method name
+         *  @return The message containing the method call.
+         */
+        sdbusplus::message::message newMethodCall(sdbusplus::bus::bus& bus,
+                                                  const char *intf,
+                                                  const char *method);
+    private:
+        /** @brief DBUS interface provided by the service */
+        const std::string intf;
+        /** @brief DBUS path provided by the service */
+        const std::string path;
+        /** @brief The name of the service if valid */
+        std::experimental::optional<std::string> cachedService;
+        /** @brief The name of the bus used in the service lookup */
+        std::experimental::optional<std::string> cachedBusName;
+
+        /** @brief Check to see if the current cache is valid
+         *
+         * @param[in] bus - The bus used for the service lookup
+         * @return True if the cache is valid false otherwise.
+         */
+        bool isValid(sdbusplus::bus::bus& bus) const;
+};
+
 /**
  * @brief Get the DBUS Service name for the input dbus path
  *
-- 
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