1 files changed, 118 insertions, 0 deletions
diff --git a/src/common/config_obs_mgr.h b/src/common/config_obs_mgr.h
new file mode 100644
index 000000000..06b3cf934
--- /dev/null
+++ b/src/common/config_obs_mgr.h
@@ -0,0 +1,118 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+
+#pragma once
+
+#include <map>
+#include <set>
+#include <string>
+
+#include "common/config_tracker.h"
+
+class ConfigValues;
+
+// @c ObserverMgr manages a set of config observers which are interested in
+// the changes of settings at runtime.
+template<class ConfigObs>
+class ObserverMgr : public ConfigTracker {
+  // Maps configuration options to the observer listening for them.
+  using obs_map_t = std::multimap<std::string, ConfigObs*>;
+  obs_map_t observers;
+
+public:
+  typedef std::map<ConfigObs*, std::set<std::string>> rev_obs_map;
+  typedef std::function<void(ConfigObs*, const std::string&)> config_gather_cb;
+
+  // Adds a new observer to this configuration. You can do this at any time,
+  // but it will only receive notifications for the changes that happen after
+  // you attach it, obviously.
+  //
+  // Most developers will probably attach their observers after global_init,
+  // but before anyone can call injectargs.
+  //
+  // The caller is responsible for allocating observers.
+  void add_observer(ConfigObs* observer);
+
+  // Remove an observer from this configuration.
+  // This doesn't delete the observer! If you allocated it with new(),
+  // you need to delete it yourself.
+  // This function will assert if you try to delete an observer that isn't
+  // there.
+  void remove_observer(ConfigObs* observer);
+  // invoke callback for every observers tracking keys
+  void for_each_observer(config_gather_cb callback);
+  // invoke callback for observers keys tracking the provided change set
+  template<class ConfigProxyT>
+  void for_each_change(const std::set<std::string>& changes,
+                       ConfigProxyT& proxy,
+                       config_gather_cb callback, std::ostream *oss);
+  bool is_tracking(const std::string& name) const override;
+};
+
+// we could put the implementations in a .cc file, and only instantiate the
+// used template specializations explicitly, but that forces us to involve
+// unused headers and libraries at compile-time. for instance, for instantiate,
+// to instantiate ObserverMgr for seastar, we will need to include seastar
+// headers to get the necessary types in place, but that would force us to link
+// the non-seastar binaries against seastar libraries. so, to avoid pulling
+// in unused dependencies at the expense of increasing compiling time, we put
+// the implementation in the header file.
+template<class ConfigObs>
+void ObserverMgr<ConfigObs>::add_observer(ConfigObs* observer)
+{
+  const char **keys = observer->get_tracked_conf_keys();
+  for (const char ** k = keys; *k; ++k) {
+    observers.emplace(*k, observer);
+  }
+}
+
+template<class ConfigObs>
+void ObserverMgr<ConfigObs>::remove_observer(ConfigObs* observer)
+{
+  [[maybe_unused]] bool found_obs = false;
+  for (auto o = observers.begin(); o != observers.end(); ) {
+    if (o->second == observer) {
+      observers.erase(o++);
+      found_obs = true;
+    } else {
+      ++o;
+    }
+  }
+  ceph_assert(found_obs);
+}
+
+template<class ConfigObs>
+void ObserverMgr<ConfigObs>::for_each_observer(config_gather_cb callback)
+{
+  for (const auto& [key, obs] : observers) {
+    callback(obs, key);
+  }
+}
+
+template<class ConfigObs>
+template<class ConfigProxyT>
+void ObserverMgr<ConfigObs>::for_each_change(const std::set<std::string>& changes,
+                                             ConfigProxyT& proxy,
+                                             config_gather_cb callback, std::ostream *oss)
+{
+  // create the reverse observer mapping, mapping observers to the set of
+  // changed keys that they'll get.
+  std::string val;
+  for (auto& key : changes) {
+    auto [first, last] = observers.equal_range(key);
+    if ((oss) && !proxy.get_val(key, &val)) {
+      (*oss) << key << " = '" << val << "' ";
+      if (first == last) {
+        (*oss) << "(not observed, change may require restart) ";
+      }
+    }
+    for (auto r = first; r != last; ++r) {
+      callback(r->second, key);
+    }
+  }
+}
+
+template<class ConfigObs>
+bool ObserverMgr<ConfigObs>::is_tracking(const std::string& name) const
+{
+  return observers.count(name) > 0;
+}