Simplify async_hooks logic

lib/instrumentation/async-hooks.js

@@ -3,9 +3,19 @@
 const asyncHooks = require('async_hooks')
 
 module.exports = function (ins) {
-  const asyncHook = asyncHooks.createHook({init, before, after, destroy})
-  const initState = new Map()
-  const beforeState = new Map()
+  const asyncHook = asyncHooks.createHook({init, destroy})
+  const transactions = new Map()
+
+  Object.defineProperty(ins, 'currentTransaction', {
+    get: function () {
+      const asyncId = asyncHooks.executionAsyncId()
+      return transactions.get(asyncId)
+    },
+    set: function (trans) {
+      const asyncId = asyncHooks.executionAsyncId()
+      transactions.set(asyncId, trans)
+    }
+  })
 
   asyncHook.enable()
 
@@ -15,23 +25,11 @@ module.exports = function (ins) {
     // type, which will init for each scheduled timer.
     if (type === 'TIMERWRAP') return
 
-    initState.set(asyncId, ins.currentTransaction)
-  }
-
-  function before (asyncId) {
-    if (!initState.has(asyncId)) return // in case type === TIMERWRAP
-    beforeState.set(asyncId, ins.currentTransaction)
-    ins.currentTransaction = initState.get(asyncId)
-  }
-
-  function after (asyncId) {
-    if (!initState.has(asyncId)) return // in case type === TIMERWRAP
-    ins.currentTransaction = beforeState.get(asyncId)
+    transactions.set(asyncId, ins.currentTransaction)
   }
 
   function destroy (asyncId) {
-    if (!initState.has(asyncId)) return // in case type === TIMERWRAP
-    initState.delete(asyncId)
-    beforeState.delete(asyncId)
+    if (!transactions.has(asyncId)) return // in case type === TIMERWRAP
+    transactions.delete(asyncId)
   }
 }