Implement the heuristics for garbage collection

Author: alco

lib/iex/lib/iex/history.ex

@@ -14,25 +14,83 @@ defmodule IEx.History do
 
     limit = IEx.Options.get(:history_size)
     start_counter = Process.get(:iex_history_start_counter)
-    should_collect = limit_history(start_counter, counter, limit)
+    should_collect = limit_history(start_counter, counter, limit, false)
     if should_collect do
-      IO.puts "...collecting garbage"
-      :erlang.garbage_collect
+      collect_garbage()
     end
   end
 
-  defp limit_history(_, _, limit) when limit < 0 do
+  defp limit_history(_, _, limit, _) when limit < 0 do
     false
   end
 
-  defp limit_history(counter, max_counter, limit) when max_counter - counter < limit do
+  defp limit_history(counter, max_counter, limit, should_collect) when max_counter - counter < limit do
     Process.put(:iex_history_start_counter, counter)
-    true
+    should_collect
   end
 
-  defp limit_history(counter, max_counter, limit) do
-    Process.delete({:iex_history, counter})
-    limit_history(counter+1, max_counter, limit)
+  defp limit_history(counter, max_counter, limit, should_collect) do
+    if not should_collect do
+      entry = Process.delete({:iex_history, counter})
+      should_collect = has_binary(entry.result)
+    else
+      Process.delete({:iex_history, counter})
+    end
+    limit_history(counter+1, max_counter, limit, should_collect)
+  end
+
+  # Checks val and each of its elements (if it is a list or a tuple)
+  # recursively to see if it has any binaries
+  defp has_binary(val) do
+    try do
+      has_bin(val)
+    catch
+      :throw, true -> true
+    end
+  end
+
+  # Worker function used by has_binary. Throws when the first binary of the
+  # minimum specified size is found
+  defp has_bin(val) when is_tuple(val) do
+    has_bin(val, tuple_size(val)-1)
+  end
+
+  defp has_bin([h|t]) do
+    has_bin(h)
+    has_bin(t)
+  end
+
+  defp has_bin(val) when byte_size(val) > 64 do
+    throw true
+  end
+
+  defp has_bin(_) do
+    false
+  end
+
+  defp has_bin(_, -1) do
+    false
+  end
+
+  defp has_bin(tuple, index) do
+    has_bin(elem(tuple, index))
+    has_bin(tuple, index-1)
+  end
+
+  # Based on https://github.com/erlang/otp/blob/7dcccee4371477e983f026db9e243cb66900b1ef/lib/stdlib/src/shell.erl#L1401
+  defp collect_garbage do
+    :erlang.garbage_collect(self())
+    try do
+      :erlang.garbage_collect(Process.whereis(:user))
+    catch
+      _, _ -> nil
+    end
+    try do
+      :erlang.garbage_collect(Process.group_leader())
+    catch
+      _, _ -> nil
+    end
+    :erlang.garbage_collect()
   end
 
   ### each ###