implement sd_notify support

Author: Matt Pelland

README.md

@@ -50,18 +50,28 @@ as follows:
       provides the API to sysadmin
     - [yaml-cpp](https://github.com/jbeder/yaml-cpp) provides YAML config file support
 
+Systemd Integration
+===================
+
+sysadmin can integrate with systemd as a `notify` type service which can
+prevent races between other services that rely on sysadmin for configuration.
+In order to build sysadmin with systemd notify support you need to pass
+`-DSYSADMIN_USE_SD_NOTIFY` during step 3 outlined below. When building sysadmin
+in this configuration `libsystemd` becomes a required dependency.
+
+There is an a systemd service definition which incorporates this functionality
+located [here](configs/prod/systemd-notify.service).
+
 Development
 ===========
 
 Generally speaking, build as follows:
 
-```
-mkdir build
-cd build
-cmake ..
-make check
-make
-```
+1. mkdir build
+2. cd build
+3. cmake ..
+4. make check
+5. make
 
 `make check` runs only sysadmin's tests. If you wish to run the decibel-cpp tests, run
 `make decibel-check`.

cmake/FindSystemd.cmake

@@ -0,0 +1,40 @@
+#.rst:
+# FindSystemd
+# -------
+#
+# Find Systemd library
+#
+# Try to find Systemd library on UNIX systems. The following values are defined
+#
+# ::
+#
+#   SYSTEMD_FOUND         - True if Systemd is available
+#   SYSTEMD_INCLUDE_DIRS  - Include directories for Systemd
+#   SYSTEMD_LIBRARIES     - List of libraries for Systemd
+#   SYSTEMD_DEFINITIONS   - List of definitions for Systemd
+#
+#=============================================================================
+# Copyright (c) 2015 Jari Vetoniemi
+#
+# Distributed under the OSI-approved BSD License (the "License");
+#
+# This software is distributed WITHOUT ANY WARRANTY; without even the
+# implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+# See the License for more information.
+#=============================================================================
+
+include(FeatureSummary)
+set_package_properties(Systemd PROPERTIES
+   URL "http://freedesktop.org/wiki/Software/systemd/"
+   DESCRIPTION "System and Service Manager")
+
+find_package(PkgConfig)
+pkg_check_modules(PC_SYSTEMD QUIET libsystemd)
+find_library(SYSTEMD_LIBRARIES NAMES systemd ${PC_SYSTEMD_LIBRARY_DIRS})
+find_path(SYSTEMD_INCLUDE_DIRS systemd/sd-login.h HINTS ${PC_SYSTEMD_INCLUDE_DIRS})
+
+set(SYSTEMD_DEFINITIONS ${PC_SYSTEMD_CFLAGS_OTHER})
+
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(SYSTEMD DEFAULT_MSG SYSTEMD_INCLUDE_DIRS SYSTEMD_LIBRARIES)
+mark_as_advanced(SYSTEMD_INCLUDE_DIRS SYSTEMD_LIBRARIES SYSTEMD_DEFINITIONS)

configs/prod/sysadmin-notify.service

@@ -0,0 +1,12 @@
+[Unit]
+Description=Sysadmin
+After=network.target syslog.target
+
+[Service]
+Type=notify
+ExecStart=/bin/sysadmin /etc/sysadmin/config.yaml
+Restart=always
+RestartSec=30
+
+[Install]
+WantedBy=multi-user.target

decibel-cpp/include/decibel/messaging/Reactor.h

@@ -70,9 +70,7 @@ class Reactor : public folly::Timekeeper
         return pPromise->getFuture();
     }
 
-    // This is kept around for posterity should anyone want to add back
-    // folly::Executor functionality
-    // virtual void add(folly::Func fn);
+    virtual void add(folly::Func fn);
 
     // folly::TimeKeeper
     virtual folly::Future<folly::Unit> after(folly::Duration duration);

decibel-cpp/src/decibel/messaging/Reactor.cpp

@@ -152,12 +152,10 @@ void Reactor::CancelCall(std::shared_ptr<OneShotTimerEvent> pTimer)
     pTimer->Stop();
 }
 
-// This is kept around for posterity should anyone want to add back
-// folly::Executor functionality
-// void Reactor::add(folly::Func fn)
-// {
-//     CallSoon(fn);
-// }
+void Reactor::add(folly::Func fn)
+{
+    CallSoon(fn);
+}
 
 folly::Future<folly::Unit> Reactor::after(folly::Duration duration)
 {

src/CMakeLists.txt

@@ -72,5 +72,15 @@ target_link_libraries(libsysadmin INTERFACE ${LIBS} decibel)
 target_include_directories(libsysadmin PUBLIC ${CMAKE_BINARY_DIR} ${PROJECT_SOURCE_DIR})
 target_link_libraries(sysadmin libsysadmin)
 
+if(SYSADMIN_USE_SD_NOTIFY)
+    include(FindSystemd)
+    find_package(Systemd REQUIRED)
+
+    target_link_libraries(sysadmin ${SYSTEMD_LIBRARIES})
+    target_include_directories(sysadmin PRIVATE ${SYSTEMD_INCLUDE_DIRS})
+
+    target_compile_definitions(sysadmin PRIVATE _SYSADMIN_USE_SD_NOTIFY)
+endif()
+
 install(TARGETS sysadmin
         RUNTIME DESTINATION bin)

src/sysadmin.cpp

@@ -1,4 +1,9 @@
 #include <iostream>
+
+#ifdef _SYSADMIN_USE_SD_NOTIFY
+#include <systemd/sd-daemon.h>
+#endif
+
 #include <boost/filesystem.hpp>
 #include <log4cxx/logger.h>
 #include <log4cxx/propertyconfigurator.h>
@@ -103,6 +108,16 @@ int main(int argc, const char* argv[])
             protocol->Send(errResponse);
         });
 
+#ifdef _SYSADMIN_USE_SD_NOTIFY
+    reactor.add([]() {
+        auto rc = sd_notify(1, "READY=1");
+
+        if (rc < 0) {
+            LOG4CXX_WARN(spLogger, "Failed to notify systemd, error: " << rc);
+        }
+    });
+#endif
+
     LOG4CXX_INFO(spLogger, "Starting sysadmin on port " << config.port);
     reactor.ServeTcp(config.host, config.port, &factory);
     reactor.Start();