Make coroutine mappings weak (and document them).

(x)pcall uses coroutines internally to allow yielding. The internal
mapping tables for those coroutines (and the initial coroutine that
started the pcall) should not keep the threads alive if the (x)pcall
yields and is never resumed again.

1 files changed, 18 insertions, 7 deletions

diff --git a/compat53.lua b/compat53.lua
index 84ef101..919ab33 100644
--- a/compat53.lua
+++ b/compat53.lua
@@ -328,12 +328,21 @@ if lua_version < "5.3" then
         #setmetatable({}, { __len = function() return 1 end }) == 1
 
 
-      -- table that maps each running coroutine to the coroutine that resumed it
-      -- this is used to build complete tracebacks when "coroutine-friendly" pcall
-      -- is used.
-      local pcall_previous = {}
-      local pcall_callOf = {}
-      local xpcall_running = {}
+      -- the (x)pcall implementations start a new coroutine internally
+      -- to allow yielding even in Lua 5.1. to allow for accurate
+      -- stack traces we keep track of the nested coroutine activations
+      -- in the weak tables below:
+      local weak_meta = { __mode = "kv" }
+      -- table that maps each running coroutine started by pcall to
+      -- the coroutine that resumed it (user coroutine *or* pcall
+      -- coroutine!)
+      local pcall_previous = setmetatable({}, weak_meta)
+      -- reverse of `pcall_mainOf`. maps a user coroutine to the
+      -- currently active pcall coroutine started within it
+      local pcall_callOf = setmetatable({}, weak_meta)
+      -- similar to `pcall_mainOf` but is used only while executing
+      -- the error handler of xpcall (thus no nesting is necessary!)
+      local xpcall_running = setmetatable({}, weak_meta)
       local coroutine_running = coroutine.running
 
       -- handle debug functions
@@ -618,7 +627,9 @@ if lua_version < "5.3" then
          return result
       end
 
-      local pcall_mainOf = {}
+      -- maps the internal pcall coroutines to the user coroutine that
+      -- *should* be running if pcall didn't use coroutines internally
+      local pcall_mainOf = setmetatable({}, weak_meta)
 
       if not is_luajit52 then
          function coroutine.running()