perf: Add FilenameCache to cache compute_filename results (#2904)

Changed below autoresearch implementation to just have one universal
FilenameCache

---

Add class-level caches to StacktraceInterface for two expensive per-frame
operations that repeat with identical inputs:

longest_load_path: Previously iterated $LOAD_PATH for every frame,
creating many intermediate strings. Now cached by abs_path with automatic
invalidation when $LOAD_PATH.size changes (e.g. after Bundler.require).

compute_filename: Many frames share identical abs_paths (same gem files
appear in every exception). Results are cached in separate in_app/
not_in_app hashes keyed by abs_path only, avoiding composite array keys.
Cache invalidates on project_root or $LOAD_PATH changes.

Both caches are deterministic — same inputs always produce the same
filename. The caches grow proportionally to the number of unique source
files seen, which is naturally bounded in any application.

Author: HazAT

sentry-ruby/lib/sentry/interfaces/stacktrace.rb

@@ -27,44 +27,24 @@ class Frame < Interface
       attr_accessor :abs_path, :context_line, :function, :in_app, :filename,
                   :lineno, :module, :pre_context, :post_context, :vars
 
-      def initialize(project_root, line, strip_backtrace_load_path = true)
+      def initialize(project_root, line, strip_backtrace_load_path = true, filename_cache: nil)
+        @strip_backtrace_load_path = strip_backtrace_load_path
+        @filename_cache = filename_cache
+
         @abs_path = line.file
         @function = line.method if line.method
         @lineno = line.number
         @in_app = line.in_app
         @module = line.module_name if line.module_name
-        @filename = compute_filename(project_root, strip_backtrace_load_path)
+        @filename = compute_filename
       end
 
       def to_s
         "#{@filename}:#{@lineno}"
       end
 
-      def compute_filename(project_root, strip_backtrace_load_path)
-        return if abs_path.nil?
-        return abs_path unless strip_backtrace_load_path
-
-        under_root = project_root && abs_path.start_with?(project_root)
-        prefix =
-          if under_root && in_app
-            project_root
-          elsif under_root
-            longest_load_path || project_root
-          else
-            longest_load_path
-          end
-
-        if prefix
-          prefix_str = prefix.to_s
-          offset = if prefix_str.end_with?(File::SEPARATOR)
-            prefix_str.bytesize
-          else
-            prefix_str.bytesize + 1
-          end
-          abs_path.byteslice(offset, abs_path.bytesize - offset)
-        else
-          abs_path
-        end
+      def compute_filename
+        @filename_cache&.compute_filename(abs_path, in_app, @strip_backtrace_load_path)
       end
 
       def set_context(linecache, context_lines)
@@ -84,10 +64,6 @@ def to_h(*args)
       end
 
       private
-
-      def longest_load_path
-        $LOAD_PATH.select { |path| abs_path.start_with?(path.to_s) }.max_by(&:size)
-      end
     end
   end
 end

sentry-ruby/lib/sentry/interfaces/stacktrace_builder.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "sentry/utils/filename_cache"
+
 module Sentry
   class StacktraceBuilder
     # @return [String]
@@ -47,6 +49,7 @@ def initialize(
       @backtrace_cleanup_callback = backtrace_cleanup_callback
       @strip_backtrace_load_path = strip_backtrace_load_path
       @in_app_pattern = Regexp.new("^(#{project_root}/)?#{app_dirs_pattern}") if app_dirs_pattern
+      @filename_cache = FilenameCache.new(project_root)
     end
 
     # Generates a StacktraceInterface with the given backtrace.
@@ -87,7 +90,7 @@ def build(backtrace:, &frame_callback)
     private
 
     def convert_parsed_line_into_frame(line)
-      frame = StacktraceInterface::Frame.new(project_root, line, strip_backtrace_load_path)
+      frame = StacktraceInterface::Frame.new(project_root, line, strip_backtrace_load_path, filename_cache: @filename_cache)
       frame.set_context(linecache, context_lines) if context_lines
       frame
     end

sentry-ruby/lib/sentry/utils/filename_cache.rb

@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module Sentry
+  class FilenameCache
+    def initialize(project_root)
+      @project_root = project_root
+      @load_paths = $LOAD_PATH.map(&:to_s).sort_by(&:size).reverse.freeze
+      @cache = {}
+    end
+
+    def compute_filename(abs_path, in_app, strip_backtrace_load_path)
+      return unless abs_path
+      return abs_path unless strip_backtrace_load_path
+
+      @cache.fetch(abs_path) do
+        under_root = @project_root && abs_path.start_with?(@project_root)
+        prefix =
+          if under_root && in_app
+            @project_root
+          elsif under_root
+            longest_load_path(abs_path) || @project_root
+          else
+            longest_load_path(abs_path)
+          end
+
+        @cache[abs_path] = if prefix
+          offset = if prefix.end_with?(File::SEPARATOR)
+            prefix.bytesize
+          else
+            prefix.bytesize + 1
+          end
+          abs_path.byteslice(offset, abs_path.bytesize - offset)
+        else
+          abs_path
+        end
+      end
+    end
+
+    private
+
+    def longest_load_path(abs_path)
+      @load_paths.find { |path| abs_path.start_with?(path) }
+    end
+  end
+end

sentry-ruby/spec/sentry/interfaces/stacktrace_spec.rb

@@ -12,16 +12,17 @@
     let(:lines) do
       Sentry::Backtrace.parse(raw_lines, configuration.project_root, configuration.app_dirs_pattern).lines
     end
+    let(:filename_cache) { Sentry::FilenameCache.new(configuration.project_root) }
 
     it "initializes a Frame with the correct info from the given Backtrace::Line object" do
-      first_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.first)
+      first_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.first, true, filename_cache: filename_cache)
 
       expect(first_frame.filename).to match(/base.rb/)
       expect(first_frame.in_app).to eq(false)
       expect(first_frame.function).to eq("save")
       expect(first_frame.lineno).to eq(10)
 
-      second_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.last)
+      second_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.last, true, filename_cache: filename_cache)
 
       expect(second_frame.filename).to match(/post.rb/)
       expect(second_frame.in_app).to eq(true)
@@ -30,11 +31,11 @@
     end
 
     it "does not strip load path when strip_backtrace_load_path is false" do
-      first_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.first, false)
+      first_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.first, false, filename_cache: filename_cache)
       expect(first_frame.filename).to eq(first_frame.abs_path)
       expect(first_frame.filename).to eq(raw_lines.first.split(':').first)
 
-      second_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.last, false)
+      second_frame = Sentry::StacktraceInterface::Frame.new(configuration.project_root, lines.last, false, filename_cache: filename_cache)
       expect(second_frame.filename).to eq(second_frame.abs_path)
       expect(second_frame.filename).to eq(raw_lines.last.split(':').first)
     end

sentry-ruby/spec/sentry/transport_spec.rb

@@ -342,7 +342,9 @@
             frames: frame_list_size.times.map do |zero_based_index|
               Sentry::StacktraceInterface::Frame.new(
                 "/fake/path",
-                Sentry::Backtrace::Line.parse("app.rb:#{zero_based_index + 1}:in `/'", in_app_pattern)
+                Sentry::Backtrace::Line.parse("app.rb:#{zero_based_index + 1}:in `/'", in_app_pattern),
+                true,
+                filename_cache: Sentry::FilenameCache.new("/fake/path")
               )
             end,
           )