safely create cache with tmp locked string object

Author: ggmichaelgo

lib/memory/cache.rb

@@ -64,6 +64,16 @@ def lookup_string(obj)
 			# The string report can still list unique strings longer than 200 characters
 			#   separately because the object_id of the shortened string will be different
 			@string_cache[obj] ||= String.new << obj[0, 64]
+		rescue RuntimeError => e
+			# It is possible for the String to be temporarily locked from another Fiber
+			# which raises an error when we try to use it as a hash key.
+			# ie: Socket#read locks a buffer string while reading data into it.
+			# In this case we dup the string to get an unlocked copy.
+			if e.message == "can't modify string; temporarily locked"
+				@string_cache[obj.dup] ||= String.new << obj[0, 64]
+			else
+				raise
+			end
 		end
 	end
 end

memory.gemspec

@@ -7,7 +7,7 @@ Gem::Specification.new do |spec|
 	spec.version = Memory::VERSION
 
 	spec.summary = "Memory profiling routines for Ruby 2.3+"
-	spec.authors = ["Sam Saffron", "Dave Gynn", "Samuel Williams", "Nick LaMuro", "Jonas Peschla", "Ashwin Maroli", "Søren Skovsbøll", "Richard Schneeman", "Anton Davydov", "Benoit Tigeot", "Jean Boussier", "Vincent Woo", "Andrew Grimm", "Boris Staal", "Danny Ben Shitrit", "Espartaco Palma", "Florian Schwab", "Hamdi Akoğuz", "Jaiden Mispy", "John Bachir", "Luís Ferreira", "Mike Subelsky", "Olle Jonsson", "Vasily Kolesnikov", "William Tabi"]
+	spec.authors = ["Sam Saffron", "Dave Gynn", "Samuel Williams", "Nick LaMuro", "Jonas Peschla", "Ashwin Maroli", "Søren Skovsbøll", "Richard Schneeman", "Anton Davydov", "Benoit Tigeot", "Jean Boussier", "Vincent Woo", "Andrew Grimm", "Boris Staal", "Danny Ben Shitrit", "Espartaco Palma", "Florian Schwab", "Hamdi Akoğuz", "Jaiden Mispy", "John Bachir", "Luís Ferreira", "Mike Subelsky", "Olle Jonsson", "Vasily Kolesnikov", "William Tabi", "Michael Go"]
 	spec.license = "MIT"
 
 	spec.cert_chain  = ["release.cert"]

test/memory/sampler.rb

@@ -4,6 +4,8 @@
 # Copyright, 2020-2025, by Samuel Williams.
 
 require "memory"
+require "socket"
+require "fileutils"
 
 class MyThing
 end
@@ -39,6 +41,53 @@ class MyThing
 		expect(allocation.retained).to be_truthy
 	end
 
+	it "safely captures locked string objects" do
+		socket_path = "/tmp/test_supervisor.ipc"
+		FileUtils.rm_f(socket_path)
+		
+		memory = Memory::Sampler.new
+		memory.start
+		
+		# Create server thread
+		Thread.new do
+			server = UNIXServer.new(socket_path)
+			client = server.accept
+			
+			2.times do
+				buffer = String.new(capacity: 2)
+				length_data = client.read(2, buffer) # buffer gets locked while reading
+				break unless length_data && length_data.bytesize == 2
+				
+				length = length_data.unpack1("n")
+				client.read(length)
+			end
+		ensure
+			client&.close
+			server.close
+		end
+		
+		# Create a client thread
+		Thread.new do
+			socket = UNIXSocket.new(socket_path)
+			
+			2.times do
+				message = Time.now.to_s
+				socket.write([message.bytesize].pack("n") + message)
+				puts "hello #{message}"
+				sleep(1)
+			end
+		ensure
+			socket&.close
+		end
+		
+		sleep(0.1)
+		
+		memory.stop
+		memory.report # buffer string is locked while reading ObjectSpace#each_object
+	ensure
+		FileUtils.rm_f(socket_path)
+	end
+	
 	with "#as_json" do
 		it "returns allocation count" do
 			x = nil