Do not create threads in finalisers

Author: pitr-ch

lib/concurrent/atomic/ruby_thread_local_var.rb

@@ -33,7 +33,32 @@ class RubyThreadLocalVar < AbstractThreadLocalVar
     LOCK   = Mutex.new
     ARRAYS = {} # used as a hash set
     @@next = 0
-    private_constant :FREE, :LOCK, :ARRAYS
+    QUEUE  = Queue.new
+    THREAD = Thread.new do
+      while true
+        method, i = QUEUE.pop
+        case method
+        when :thread_local_finalizer
+          LOCK.synchronize do
+            FREE.push(i)
+            # The cost of GC'ing a TLV is linear in the number of threads using TLVs
+            # But that is natural! More threads means more storage is used per TLV
+            # So naturally more CPU time is required to free more storage
+            ARRAYS.each_value do |array|
+              array[i] = nil
+            end
+          end
+        when :thread_finalizer
+          LOCK.synchronize do
+            # The thread which used this thread-local array is now gone
+            # So don't hold onto a reference to the array (thus blocking GC)
+            ARRAYS.delete(i)
+          end
+        end
+      end
+    end
+
+    private_constant :FREE, :LOCK, :ARRAYS, :QUEUE, :THREAD
 
     # @!macro thread_local_var_method_get
     def value
@@ -77,37 +102,18 @@ def allocate_storage
           result
         end
       end
-      ObjectSpace.define_finalizer(self, self.class.threadlocal_finalizer(@index))
+      ObjectSpace.define_finalizer(self, self.class.thread_local_finalizer(@index))
     end
 
     # @!visibility private
-    def self.threadlocal_finalizer(index)
-      proc do
-        Thread.new(index) do |index| # avoid error: can't be called from trap context
-          LOCK.synchronize do
-            FREE.push(index)
-            # The cost of GC'ing a TLV is linear in the number of threads using TLVs
-            # But that is natural! More threads means more storage is used per TLV
-            # So naturally more CPU time is required to free more storage
-            ARRAYS.each_value do |array|
-              array[index] = nil
-            end
-          end
-        end
-      end
+    def self.thread_local_finalizer(index)
+      proc { QUEUE.push [:thread_local_finalizer, index] }
     end
 
     # @!visibility private
     def self.thread_finalizer(id)
-      proc do
-        Thread.new(id) do |id| # avoid error: can't be called from trap context
-          LOCK.synchronize do
-            # The thread which used this thread-local array is now gone
-            # So don't hold onto a reference to the array (thus blocking GC)
-            ARRAYS.delete(id)
-          end
-        end
-      end
+      # avoid error: can't be called from trap context
+      proc { QUEUE.push [:thread_finalizer, id] }
     end
 
     private