Merge pull request #1067 from appsignal/probes-late-start

Start probes registered after thread is started

.changesets/add-probes-register-method.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "change"
+---
+
+Add `Appsignal::Probes.register` method as the preferred method to register probes. The `Appsignal::Probes.probes.register` is now deprecated.

.changesets/automatically-start-new-probes-on-register.md

@@ -0,0 +1,6 @@
+---
+bump: "patch"
+type: "change"
+---
+
+Automatically start new probes when registered with `Appsignal::Probes.register` when the gem has already started the probes thread. Previously, the late registered probes would not be run.

lib/appsignal/probes.rb

@@ -25,6 +25,50 @@ def [](key)
         probes[key]
       end
 
+      # @deprecated Use {Appsignal::Probes.register} instead.
+      def register(name, probe)
+        Appsignal::Utils::StdoutAndLoggerMessage.warning(
+          "The method 'Appsignal::Probes.probes.register' is deprecated. " \
+            "Use 'Appsignal::Probes.register' instead."
+        )
+        Appsignal::Probes.register(name, probe)
+      end
+
+      # @api private
+      def internal_register(name, probe)
+        if probes.key?(name)
+          logger.debug "A probe with the name `#{name}` is already " \
+            "registered. Overwriting the entry with the new probe."
+        end
+        probes[name] = probe
+      end
+
+      # @api private
+      def each(&block)
+        probes.each(&block)
+      end
+
+      private
+
+      attr_reader :probes
+
+      def logger
+        Appsignal.internal_logger
+      end
+    end
+
+    class << self
+      # @api private
+      def mutex
+        @mutex ||= Thread::Mutex.new
+      end
+
+      # @see ProbeCollection
+      # @return [ProbeCollection] Returns list of probes.
+      def probes
+        @probes ||= ProbeCollection.new
+      end
+
       # Register a new minutely probe.
       #
       # Supported probe types are:
@@ -40,14 +84,14 @@ def [](key)
       #   a `call` method call. The `call` method is called every minute.
       #
       # @example Register a new probe
-      #   Appsignal::Probes.probes.register :my_probe, lambda {}
+      #   Appsignal::Probes.register :my_probe, lambda {}
       #
       # @example Overwrite an existing registered probe
-      #   Appsignal::Probes.probes.register :my_probe, lambda {}
-      #   Appsignal::Probes.probes.register :my_probe, lambda { puts "hello" }
+      #   Appsignal::Probes.register :my_probe, lambda {}
+      #   Appsignal::Probes.register :my_probe, lambda { puts "hello" }
       #
       # @example Add a lambda as a probe
-      #   Appsignal::Probes.probes.register :my_probe, lambda { puts "hello" }
+      #   Appsignal::Probes.register :my_probe, lambda { puts "hello" }
       #   # "hello" # printed every minute
       #
       # @example Add a probe instance
@@ -61,7 +105,7 @@ def [](key)
       #     end
       #   end
       #
-      #   Appsignal::Probes.probes.register :my_probe, MyProbe.new
+      #   Appsignal::Probes.register :my_probe, MyProbe.new
       #   # "started" # printed immediately
       #   # "called" # printed every minute
       #
@@ -79,7 +123,7 @@ def [](key)
       #     end
       #   end
       #
-      #   Appsignal::Probes.probes.register :my_probe, MyProbe
+      #   Appsignal::Probes.register :my_probe, MyProbe
       #   Appsignal::Probes.start # This is called for you
       #   # "started" # Printed on Appsignal::Probes.start
       #   # "called" # Repeated every minute
@@ -91,37 +135,15 @@ def [](key)
       #   be used as a probe.
       # @return [void]
       def register(name, probe)
-        if probes.key?(name)
-          logger.debug "A probe with the name `#{name}` is already " \
-            "registered. Overwriting the entry with the new probe."
-        end
-        probes[name] = probe
-      end
-
-      # @api private
-      def each(&block)
-        probes.each(&block)
-      end
-
-      private
+        probes.internal_register(name, probe)
 
-      attr_reader :probes
-
-      def logger
-        Appsignal.internal_logger
-      end
-    end
-
-    class << self
-      # @see ProbeCollection
-      # @return [ProbeCollection] Returns list of probes.
-      def probes
-        @probes ||= ProbeCollection.new
+        initialize_probe(name, probe) if started?
       end
 
       # @api private
       def start
         stop
+        @started = true
         @thread = Thread.new do
           # Advise multi-threaded app servers to ignore this thread
           # for the purposes of fork safety warnings
@@ -133,22 +155,33 @@ def start
           initialize_probes
           loop do
             logger = Appsignal.internal_logger
-            logger.debug("Gathering minutely metrics with #{probe_instances.count} probes")
-            probe_instances.each do |name, probe|
-              logger.debug("Gathering minutely metrics with '#{name}' probe")
-              probe.call
-            rescue => ex
-              logger.error "Error in minutely probe '#{name}': #{ex}"
-              logger.debug ex.backtrace.join("\n")
+            mutex.synchronize do
+              logger.debug("Gathering minutely metrics with #{probe_instances.count} probes")
+              probe_instances.each do |name, probe|
+                logger.debug("Gathering minutely metrics with '#{name}' probe")
+                probe.call
+              rescue => ex
+                logger.error "Error in minutely probe '#{name}': #{ex}"
+                logger.debug ex.backtrace.join("\n")
+              end
             end
             sleep wait_time
           end
         end
       end
 
+      # Returns if the probes thread has been started. If the value is false or
+      # nil, it has not been started yet.
+      #
+      # @return [Boolean, nil]
+      def started?
+        @started
+      end
+
       # @api private
       def stop
         defined?(@thread) && @thread.kill
+        @started = false
         probe_instances.clear
       end
 
@@ -185,7 +218,9 @@ def initialize_probe(name, probe)
             "#{klass}.dependency_present? returned falsy"
           return
         end
-        probe_instances[name] = instance
+        mutex.synchronize do
+          probe_instances[name] = instance
+        end
       rescue => error
         logger = Appsignal.internal_logger
         logger.error "Error while initializing minutely probe '#{name}': #{error}"