issue #487: add listen/thread and spec

lib/listen/thread.rb

@@ -0,0 +1,43 @@
+require 'thread'
+
+require_relative 'logger'
+
+module Listen
+  module Thread
+    class << self
+      # Creates a new thread with the given name.
+      # Any exceptions raised by the thread will be logged with the thread name and complete backtrace.
+      def new(name)
+        thread_name = "listen-#{name}"
+
+        caller_stack = caller
+        ::Thread.new do
+          yield
+        rescue Exception => ex
+          _log_exception(ex, thread_name, caller_stack)
+          nil
+        end.tap do |thread|
+          thread.name = thread_name
+        end
+      end
+
+      private
+
+      def _log_exception(ex, thread_name, caller_stack)
+        complete_backtrace = [*ex.backtrace, "--- Thread.new ---", *caller_stack]
+        message = "Exception rescued in #{thread_name}:\n#{_exception_with_causes(ex)}\n#{complete_backtrace * "\n"}"
+        Listen::Logger.error(message)
+      end
+
+      def _exception_with_causes(ex)
+        result = +"#{ex.class}: #{ex}"
+        if ex.cause
+          result << "\n"
+          result << "--- Caused by: ---\n"
+          result << _exception_with_causes(ex.cause)
+        end
+        result
+      end
+    end
+  end
+end

spec/lib/listen/thread_spec.rb

@@ -0,0 +1,54 @@
+require 'listen/thread'
+
+RSpec.describe Listen::Thread do
+  let(:name) { "worker_thread" }
+  let(:block) { -> { } }
+  subject { described_class.new(name, &block) }
+
+  it "calls Thread.new" do
+    expect(Thread).to receive(:new) do
+      thread = instance_double(Thread, "thread")
+      expect(thread).to receive(:name=).with("listen-#{name}")
+      thread
+    end
+    subject
+  end
+
+  context "when exception raised" do
+    let(:block) do
+      -> { raise ArgumentError, 'boom!' }
+    end
+
+    it "rescues and logs exceptions" do
+      expect(Listen::Logger).to receive(:error)
+        .with(/Exception rescued in listen-worker_thread:\nArgumentError: boom!\n.*\/listen\/thread_spec\.rb/)
+      subject.join
+    end
+
+    it "rescues and logs backtrace + exception backtrace" do
+      expect(Listen::Logger).to receive(:error)
+        .with(/Exception rescued in listen-worker_thread:\nArgumentError: boom!\n.*\/listen\/thread\.rb.*--- Thread.new ---.*\/listen\/thread_spec\.rb/m)
+      subject.join
+    end
+  end
+
+  context "when nested exceptions raised" do
+    let(:block) do
+      -> do
+        begin
+          raise ArgumentError, 'boom!'
+        rescue
+          raise 'nested inner'
+        end
+      rescue
+        raise 'nested outer'
+      end
+    end
+
+    it "details exception causes" do
+      expect(Listen::Logger).to receive(:error)
+        .with(/RuntimeError: nested outer\n--- Caused by: ---\nRuntimeError: nested inner\n--- Caused by: ---\nArgumentError: boom!/)
+      subject.join
+    end
+  end
+end