From fdb52e0243b45212327111b2602663021dcafe68 Mon Sep 17 00:00:00 2001
From: Joe Cheng <joe@rstudio.com>
Date: Wed, 10 Aug 2016 14:50:46 -0700
Subject: [PATCH] executeElapsed gets stuck returning TRUE even when nothing
 was executed

Fixes #1278
---
 NEWS                        |  3 +++
 R/timer.R                   |  7 ++++++-
 tests/testthat/test-timer.R | 25 +++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 tests/testthat/test-timer.R

diff --git a/NEWS b/NEWS
index a5a110b00..259b36207 100644
--- a/NEWS
+++ b/NEWS
@@ -87,6 +87,9 @@ shiny 0.13.2.9005
 * Fixed #1253: Memory could leak when an observer was destroyed without first
   being invalidated.
 
+* Fixed #1284: Reactive system was being flushed too often (usually this just
+  means a more-expensive no-op than necessary).
+
 shiny 0.13.2
 --------------------------------------------------------------------------------
 
diff --git a/R/timer.R b/R/timer.R
index aee7a1801..51f237bd3 100644
--- a/R/timer.R
+++ b/R/timer.R
@@ -22,6 +22,11 @@ TimerCallbacks <- R6Class(
       .times <<- data.frame()
     },
     schedule = function(millis, func) {
+      # If args could fail to evaluate, let's make them do that before
+      # we change any state
+      force(millis)
+      force(func)
+
       id <- .nextId
       .nextId <<- .nextId + 1L
 
@@ -56,7 +61,7 @@ TimerCallbacks <- R6Class(
     },
     executeElapsed = function() {
       elapsed <- takeElapsed()
-      if (length(elapsed) == 0)
+      if (nrow(elapsed) == 0)
         return(FALSE)
 
       for (id in elapsed$id) {
diff --git a/tests/testthat/test-timer.R b/tests/testthat/test-timer.R
new file mode 100644
index 000000000..f4aef724b
--- /dev/null
+++ b/tests/testthat/test-timer.R
@@ -0,0 +1,25 @@
+context("timer")
+
+test_that("Scheduling works", {
+  ran <- FALSE
+  fun <- function() {
+    ran <<- TRUE
+  }
+
+  timerCallbacks$schedule(500, fun)
+
+  timerCallbacks$executeElapsed()
+  expect_false(ran)
+
+  Sys.sleep(0.1)
+  timerCallbacks$executeElapsed()
+  expect_false(ran)
+
+  Sys.sleep(0.5)
+  expect_true(timerCallbacks$executeElapsed())
+  expect_true(ran)
+
+  # Empty timerCallbacks should return FALSE
+  expect_false(timerCallbacks$executeElapsed())
+  expect_equal(0, nrow(timerCallbacks$takeElapsed()))
+})