From 2565d3d102efd21ba02ed1f3b96d892fe2637d2b Mon Sep 17 00:00:00 2001
From: PMunch <peterme@peterme.net>
Date: Sun, 22 Sep 2019 07:24:14 +0200
Subject: [PATCH] Fix issue with long wait for passed timer [bugfix] (#12221)

* Fix issue with long wait for passed timer [bugfix]

This fixes a small issue where a timer that had been completed while
code executed would still wait for more events before being considered
completed. This would in some scenarios incur a 500ms delay to the
completion of a timer.

* Refactor logic into

* Add test case based on original issue

* Use longer timeouts to be more lenient in checking

* Revert to short timeouts, but widen the accepted range

* Widen accepted range further, it is meant to check for a 500ms delay after all

* Increase poll timeout to make it easier to detect mistakes
---
 lib/pure/asyncdispatch.nim | 12 ++++++---
 tests/async/t12221.nim     | 52 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 3 deletions(-)
 create mode 100644 tests/async/t12221.nim

diff --git a/lib/pure/asyncdispatch.nim b/lib/pure/asyncdispatch.nim
index 7c1b701b81..f4dc3de392 100644
--- a/lib/pure/asyncdispatch.nim
+++ b/lib/pure/asyncdispatch.nim
@@ -210,7 +210,12 @@ proc processPendingCallbacks(p: PDispatcherBase; didSomeWork: var bool) =
     cb()
     didSomeWork = true
 
-proc adjustTimeout(pollTimeout: int, nextTimer: Option[int]): int {.inline.} =
+proc adjustTimeout(
+  p: PDispatcherBase, pollTimeout: int, nextTimer: Option[int]
+): int {.inline.} =
+  if p.callbacks.len != 0:
+    return 0
+
   if nextTimer.isNone() or pollTimeout == -1:
     return pollTimeout
 
@@ -324,7 +329,7 @@ when defined(windows) or defined(nimdoc):
 
     result = false
     let nextTimer = processTimers(p, result)
-    let at = adjustTimeout(timeout, nextTimer)
+    let at = adjustTimeout(p, timeout, nextTimer)
     var llTimeout =
       if at == -1: winlean.INFINITE
       else: at.int32
@@ -1284,7 +1289,8 @@ else:
     result = false
     var keys: array[64, ReadyKey]
     let nextTimer = processTimers(p, result)
-    var count = p.selector.selectInto(adjustTimeout(timeout, nextTimer), keys)
+    var count =
+      p.selector.selectInto(adjustTimeout(p, timeout, nextTimer), keys)
     for i in 0..<count:
       let fd = keys[i].fd.AsyncFD
       let events = keys[i].events
diff --git a/tests/async/t12221.nim b/tests/async/t12221.nim
new file mode 100644
index 0000000000..a6ccfb060e
--- /dev/null
+++ b/tests/async/t12221.nim
@@ -0,0 +1,52 @@
+import asyncdispatch, os, times
+
+proc doubleSleep(hardSleep: int) {.async.} =
+  await sleepAsync(100)
+  sleep(hardSleep)
+
+template assertTime(target, timeTook: float): untyped {.dirty.} =
+  assert(timeTook*1000 > target - 1000, "Took too short, should've taken " &
+    $target & "ms, but took " & $(timeTook*1000) & "ms")
+  assert(timeTook*1000 < target + 1000, "Took too long, should've taken " &
+    $target & "ms, but took " & $(timeTook*1000) & "ms")
+
+var
+  start: float
+  fut: Future[void]
+
+# NOTE: this uses poll(3000) to limit timing error potential.
+start = epochTime()
+fut = sleepAsync(50) and sleepAsync(150) and doubleSleep(40)
+while not fut.finished:
+  poll(3000)
+assertTime(150, epochTime() - start)
+
+start = epochTime()
+fut = sleepAsync(50) and sleepAsync(150) and doubleSleep(100)
+while not fut.finished:
+  poll(3000)
+assertTime(200, epochTime() - start)
+
+start = epochTime()
+fut = sleepAsync(50) and sleepAsync(150) and doubleSleep(40) and sleepAsync(300)
+while not fut.finished:
+  poll(3000)
+assertTime(300, epochTime() - start)
+
+start = epochTime()
+fut = sleepAsync(50) and sleepAsync(150) and doubleSleep(100) and sleepAsync(300)
+while not fut.finished:
+  poll(3000)
+assertTime(300, epochTime() - start)
+
+start = epochTime()
+fut = (sleepAsync(50) and sleepAsync(150) and doubleSleep(40)) or sleepAsync(700)
+while not fut.finished:
+  poll(3000)
+assertTime(150, epochTime() - start)
+
+start = epochTime()
+fut = (sleepAsync(50) and sleepAsync(150) and doubleSleep(100)) or sleepAsync(700)
+while not fut.finished:
+  poll(3000)
+assertTime(200, epochTime() - start)