Better observer state handling.

Author: ioquatix

lib/async/utilization/metric.rb

@@ -11,16 +11,26 @@ module Utilization
 		# including the buffer, offset, and type. When the observer changes, the cache
 		# is invalidated and rebuilt on the next access.
 		class Metric
+			# Create a new metric for the given field and observer.
+			#
+			# @parameter field [Symbol] The field name for this metric.
+			# @parameter observer [Observer | Nil] The observer to associate with this metric.
+			# @returns [Metric] A new metric instance.
+			def self.for(field, observer)
+				self.new(field).tap do |metric|
+					metric.observer = observer
+				end
+			end
+			
 			# Initialize a new metric.
 			#
 			# @parameter name [Symbol] The field name for this metric.
-			# @parameter registry [Registry] The registry instance to use.
-			def initialize(name, registry)
+			def initialize(name)
 				@name = name.to_sym
-				@registry = registry
 				@value = 0
-				@cache_valid = false
-				@cached_field_info = nil
+				
+				@observer = nil
+				@cached_field = nil
 				@cached_buffer = nil
 				@guard = Mutex.new
 			end
@@ -34,19 +44,35 @@ def initialize(name, registry)
 			# @attribute [Mutex] The mutex for thread safety.
 			attr :guard
 
-			# Invalidate the cached field information.
+			# Set the observer and rebuild cache.
 			#
-			# Called when the observer changes to force cache rebuild.
-			def invalidate
-				@cache_valid = false
-				@cached_field_info = nil
-				@cached_buffer = nil
+			# This is called when the registry assigns a new observer (or removes it).
+			# The cache is invalidated and then immediately recomputed so that the
+			# fast write path doesn't need to re-check the observer on the first write.
+			#
+			# @parameter observer [Observer | Nil] The new observer (or nil).
+			def observer=(observer)
+				@guard.synchronize do
+					@observer = observer
+					
+					if @observer
+						if field = @observer.schema[@name]
+							if buffer = @observer.buffer
+								@cached_field = field
+								@cached_buffer = buffer
+								
+								return write_direct(@value)
+							end
+						end
+					end
+					
+					@cached_field = nil
+					@cached_buffer = nil
+				end
 			end
 
 			# Increment the metric value.
 			#
-			# Uses the fast path (direct buffer write) when cache is valid and observer is available.
-			#
 			# @returns [Integer] The new value of the field.
 			def increment
 				@guard.synchronize do
@@ -103,28 +129,6 @@ def set(value)
 
 			protected
 
-			# Check if the cache is valid and rebuild if necessary.
-			#
-			# Always attempts to build the cache if it's invalid. Returns true if cache
-			# is now valid (observer exists, field is in schema, and buffer is available), false otherwise.
-			#
-			# @returns [bool] True if cache is valid, false otherwise.
-			def ensure_cache_valid!
-				unless @cache_valid
-					if observer = @registry.observer
-						if field = observer.schema[@name]
-							if buffer = observer.buffer
-								@cached_field_info = field
-								@cached_buffer = buffer
-							end
-						end
-					end
-					
-					# Once we've validated the cache, even if there was no observer or buffer, we mark it as valid, so that we don't try to revalidate it again:
-					@cache_valid = true
-				end
-			end
-			
 			# Write directly to the cached buffer if available.
 			#
 			# This is the fast path that avoids hash lookups. Always ensures cache is valid
@@ -133,16 +137,12 @@ def ensure_cache_valid!
 			# @parameter value [Numeric] The value to write.
 			# @returns [Boolean] Whether the write succeeded.
 			def write_direct(value)
-				self.ensure_cache_valid!
-				
 				if @cached_buffer
-					@cached_buffer.set_value(@cached_field_info.type, @cached_field_info.offset, value)
+					@cached_buffer.set_value(@cached_field.type, @cached_field.offset, value)
 				end
 
 				return true
 			rescue => error
-				# If write fails, log warning but don't invalidate cache
-				# The error might be transient, and invalidating would force hash lookups
 				Console.warn(self, "Failed to write metric value!", metric: {name: @name, value: value}, exception: error)
 
 				return false

lib/async/utilization/observer.rb

@@ -3,7 +3,6 @@
 # Released under the MIT License.
 # Copyright, 2026, by Samuel Williams.
 
-require "console"
 require_relative "schema"
 
 module Async
@@ -71,21 +70,6 @@ def initialize(schema, buffer)
 
 			# @attribute [IO::Buffer] The mapped buffer for shared memory.
 			attr :buffer
-			
-			# Set a field value.
-			#
-			# Writes the value to shared memory at the offset defined by the schema.
-			# Only fields defined in the schema will be written.
-			#
-			# @parameter field [Symbol] The field name to set.
-			# @parameter value [Numeric] The value to set.
-			def set(field, value)
-				if field = @schema[field]
-					@buffer.set_value(field.type, field.offset, value)
-				end
-			rescue => error
-				Console.warn(self, "Failed to set field in shared memory!", field: field, exception: error)
-			end
 		end
 	end
 end

lib/async/utilization/registry.rb

@@ -3,6 +3,8 @@
 # Released under the MIT License.
 # Copyright, 2026, by Samuel Williams.
 
+require "console"
+
 module Async
 	module Utilization
 		# Registry for emitting utilization metrics.
@@ -61,26 +63,23 @@ def values
 
 			# Set the observer for the registry.
 			#
-			# When an observer is set, it is notified of all current metric values
-			# so it can sync its state. The observer must implement `set(field, value)`.
-			# All cached metrics are invalidated when the observer changes.
+			# When an observer is set, all cached metrics are updated so they write
+			# directly to the observer's buffer. The observer must expose `schema`
+			# and `buffer` attributes.
 			#
-			# @parameter observer [#set] The observer to set.
+			# @parameter observer [Observer | Nil] The observer to set.
 			def observer=(observer)
 				@guard.synchronize do
-					# Invalidate all cached metrics
+					@observer = observer
+					
+					# Invalidate all cached metrics with new observer (or nil)
 					@metrics.each_value do |metric|
-						metric.invalidate
+						metric.observer = observer
 					end
 
-					@observer = observer
+					# Console.info(self, "Observer assigned", observer: observer, metric_count: @metrics.size)
 				end
 
-				# Notify observer of all current metric values (outside guard to avoid deadlock)
-				@metrics.each do |name, metric|
-					value = metric.guard.synchronize{metric.value}
-					observer.set(name, value)
-				end
 			end
 
 			# Set a field value.
@@ -135,7 +134,7 @@ def metric(field)
 				field = field.to_sym
 
 				@guard.synchronize do
-					@metrics[field] ||= Metric.new(field, self)
+					@metrics[field] ||= Metric.for(field, @observer)
 				end
 			end
 		end

releases.md

@@ -1,5 +1,9 @@
 # Releases
 
+## Unreleased
+
+  - Better observer state handling.
+
 ## v0.3.1
 
   - Remove unused `thread-local` dependency.

test/async/utilization/metric.rb

@@ -154,8 +154,8 @@
 	end
 
 	it "writes directly to shared memory when observer is set" do
-		registry.observer = observer
 		metric = registry.metric(:total_requests)
+		registry.observer = observer
 
 		metric.set(42)
 
@@ -216,33 +216,13 @@
 		expect(metric1).to be == metric2
 	end
 
-	it "falls back to observer.set when write_direct fails" do
-		registry.observer = observer
-		metric = registry.metric(:total_requests)
-		
-		# Force cache to be invalid by invalidating it
-		metric.invalidate
-		
-		# Set a value - should fall back to observer.set
-		metric.set(42)
-		expect(metric.value).to be == 42
-		
-		# Verify it was written to shared memory
-		buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
-		expect(buffer.get_value(:u64, 0)).to be == 42
-	end
-	
 	it "handles write errors gracefully" do
 		registry.observer = observer
 		metric = registry.metric(:total_requests)
 
 		# Set a value first to build the cache
 		metric.set(10)
 
-		# Verify cache is built
-		expect(metric.instance_variable_get(:@cache_valid)).to be == true
-		cached_buffer = metric.instance_variable_get(:@cached_buffer)
-		
 		# Create an invalid buffer that will raise an error
 		invalid_buffer = Object.new
 		def invalid_buffer.set_value(type, offset, value)
@@ -251,18 +231,38 @@ def invalid_buffer.set_value(type, offset, value)
 
 		metric.instance_variable_set(:@cached_buffer, invalid_buffer)
 
-		# Should not raise, but log warning and keep cache valid
+		# Should not raise, but log warning
 		metric.set(42)
 		expect(metric.value).to be == 42
 
-		# Cache should remain valid (not invalidated on error)
-		expect(metric.instance_variable_get(:@cache_valid)).to be == true
-		
 		# Assert that a warning was logged
 		expect_console.to have_logged(
 			severity: be == :warn,
 			subject: be_a(Async::Utilization::Metric),
 			message: be == "Failed to write metric value!"
 		)
 	end
+	
+	it "clears cache when observer is removed" do
+		registry.observer = observer
+		metric = registry.metric(:total_requests)
+		metric.set(10)
+		
+		# Remove observer — cache should be cleared
+		registry.observer = nil
+		
+		# Write should not go to the old buffer
+		metric.set(99)
+		
+		buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
+		expect(buffer.get_value(:u64, 0)).to be == 10
+		
+		# In-memory value is still updated
+		expect(metric.value).to be == 99
+		
+		# Re-attaching observer should sync the current value
+		registry.observer = observer
+		buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
+		expect(buffer.get_value(:u64, 0)).to be == 99
+	end
 end

test/async/utilization/observer.rb

@@ -4,13 +4,11 @@
 # Copyright, 2026, by Samuel Williams.
 
 require "sus"
-require "sus/fixtures/console/captured_logger"
 require "sus/fixtures/temporary_directory_context"
 require "async/utilization"
 require "fileutils"
 
 describe Async::Utilization::Observer do
-	include Sus::Fixtures::Console::CapturedLogger
 	include Sus::Fixtures::TemporaryDirectoryContext
 
 	let(:shm_path) {File.join(root, "test.shm")}
@@ -41,68 +39,30 @@
 		expect(observer.schema).to be == schema
 	end
 
-	it "can write values to shared memory" do
-		observer.set(:total_requests, 42)
-		observer.set(:active_requests, 5)
-		
-		# Read back from file to verify
-		buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
-		expect(buffer.get_value(:u64, 0)).to be == 42
-		expect(buffer.get_value(:u32, 8)).to be == 5
-	end
-	
 	with "non-page-aligned offsets" do
 		let(:file_size) {IO::Buffer::PAGE_SIZE * 2}
 		let(:offset) {100}  # Not page-aligned
 
-		it "handles non-page-aligned offsets" do
-			observer.set(:total_requests, 100)
-			observer.set(:active_requests, 20)
+		it "maps values at the correct offset" do
+			observer.buffer.set_value(:u64, schema[:total_requests].offset, 100)
+			observer.buffer.set_value(:u32, schema[:active_requests].offset, 20)
 
-			# Read back from file at the correct offset
+			# Read back from file at the correct byte position
 			buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
-			expect(buffer.get_value(:u64, offset)).to be == 100
-			expect(buffer.get_value(:u32, offset + 8)).to be == 20
+			expect(buffer.get_value(:u64, offset + schema[:total_requests].offset)).to be == 100
+			expect(buffer.get_value(:u32, offset + schema[:active_requests].offset)).to be == 20
 		end
 	end
 
-	it "ignores fields not in schema" do
-		# Should not raise an error
-		observer.set(:unknown_field, 999)
-		
-		# Verify nothing was written
-		buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
-		expect(buffer.get_value(:u64, 0)).to be == 0
-	end
-	
 	with "page-aligned offsets" do
 		let(:file_size) {page_size * 2}
 		let(:segment_size) {page_size}
 
-		it "handles page-aligned offsets without slicing" do
-			expect(observer).to be_a(Async::Utilization::Observer)
-			observer.set(:total_requests, 123)
+		it "maps values at the correct offset" do
+			observer.buffer.set_value(:u64, schema[:total_requests].offset, 123)
 
-			# Verify value was written
 			buffer = IO::Buffer.map(File.open(shm_path, "r+b"), file_size, 0)
-			expect(buffer.get_value(:u64, 0)).to be == 123
+			expect(buffer.get_value(:u64, schema[:total_requests].offset)).to be == 123
 		end
 	end
-	
-	it "handles errors gracefully when setting values" do
-		# Create an invalid buffer that will cause an error
-		# We'll mock the buffer to raise an error
-		buffer = observer.instance_variable_get(:@buffer)
-		expect(buffer).to receive(:set_value).and_raise(IOError, "Buffer error")
-		
-		# Should not raise, but log a warning
-		observer.set(:total_requests, 42)
-		
-		# Assert that a warning was logged
-		expect_console.to have_logged(
-			severity: be == :warn,
-			subject: be_a(Async::Utilization::Observer),
-			message: be == "Failed to set field in shared memory!"
-		)
-	end
 end