1 files changed, 26 insertions, 23 deletions

diff --git a/lib/utils.coffee b/lib/utils.coffee
index 51b16351..b0abfd8f 100644
--- a/lib/utils.coffee
+++ b/lib/utils.coffee
@@ -212,24 +212,45 @@ globalRoot.extend = (hash1, hash2) ->
 
 # A simple cache. Entries used within two expiry periods are retained, otherwise they are discarded.
 # At most 2 * @entries entries are retained.
+#
+# Note.  We need to be careful with @timer.  If all references to a cache are lost, then eventually its
+# contents must be garbage collected, which will not happen if there are active timers.
 class SimpleCache
   # expiry: expiry time in milliseconds (default, one hour)
   # entries: maximum number of entries in @cache (there may be this many entries in @previous, too)
   constructor: (@expiry = 60 * 60 * 1000, @entries = 1000) ->
     @cache = {}
-    @rotate() # Force start the rotation timer.
+    @previous = {}
+    @timer = null
 
   rotate: ->
     @previous = @cache
     @cache = {}
     # We reset the timer every time the cache is rotated (which could be because a previous timer expired, or
-    # because the number of @entries was exceeded.
+    # because the number of @entries was exceeded).  We only restart the timer if the cache is not empty.
     clearTimeout @timer if @timer?
-    @timer = Utils.setTimeout @expiry, => @rotate()
+    @timer = null
+    @checkTimer() if 0 < Object.keys(@previous).length
+
+  checkTimer: ->
+    unless @timer?
+      @timer = Utils.setTimeout @expiry, => @rotate()
 
   has: (key) ->
     (key of @cache) or key of @previous
 
+  # Set value, and return that value.  If value is null, then delete key.
+  set: (key, value = null) ->
+    @checkTimer()
+    if value?
+      @cache[key] = value
+      delete @previous[key]
+      @rotate() if @entries < Object.keys(@cache).length
+    else
+      delete @cache[key]
+      delete @previous[key]
+    value
+
   get: (key) ->
     if key of @cache
       @cache[key]
@@ -242,27 +263,9 @@ class SimpleCache
     @rotate()
     @rotate()
 
-  # Because of the timer, we can't just let these caches go out of scope and have the garbage collector
-  # harvest them.  Whenever they may fall out of use, we need to remove the timer. @rotate() can be used to
-  # restart the cache.
-  suspend: ->
-    clearTimeout @timer if @timer?
-    @timer = null
-
-  # Set value, and return that value.  If value is null, then delete key.
-  set: (key, value = null) ->
-    if value?
-      @cache[key] = value
-      delete @previous[key]
-      @rotate() if @entries < Object.keys(@cache).length
-    else
-      delete @cache[key]
-      delete @previous[key]
-    value
-
 # This is a simple class for the common case where we want to use some data value which may be immediately
-# available, or we may have to wait.  It implements the use-immediately-or-wait queue, and calls the function
-# to fetch the data asynchronously.
+# available, or for which we may have to wait.  It implements the use-immediately-or-wait queue, and calls the
+# function to fetch the data asynchronously.
 class AsyncDataFetcher
   constructor: (fetch) ->
     @data = null