make CI tests faster + more precise

tests/gc/gcleak2.nim

@@ -2,6 +2,11 @@ discard """
   outputsub: "no leak: "
 """
 
+## this test makes sure getOccupiedMem() is constant after a few iterations
+## for --gc:bohem, --gc:markAndSweep, --gc:arc, --gc:orc.
+## and for other gc, it consists of cycles with constant min/max after a few cycles.
+## This ensures we have no leaks.
+
 when defined(GC_setMaxPause):
   GC_setMaxPause 2_000
 
@@ -14,13 +19,75 @@ proc makeObj(): TTestObj =
   result.x = "Hello"
   result.s = @[1,2,3]
 
+const collectAlways = defined(gcMarkAndSweep) or defined(boehmgc)
+const isDeterministic = collectAlways or defined(gcArc) or defined(gcOrc)
+  ## when isDeterministic, we expect memory to reach a fixed point
+  ## after `numIterStable` iterations
+
+var memMax = 0 # peak
+
+when isDeterministic:
+  const numIterStable = 3
+    # stabilize after this many iterations
+else:
+  const numCycleStable = when defined(useRealtimeGC): 6 else: 4
+    # stabilize after this many cycles; empirically determined
+    # after running all combinations of gc's with / without -d:release
+  var memPrevious = 0
+  var memMin = int.high # right after a peak
+  var numCollections = 0
+
+let numIter = when isDeterministic: 1_000 else: 1_000_000
+  ## full collection is expensive, and the memory doesn't change after
+  ## each iteration so there's no point in a large `numIter` (this was taking
+  ## 350s for `nim c -r -d:release --gc:boehm` + `nim c -r --gc:boehm`, 50%
+  ## of running time of `testament/testament all`.
+
 proc inProc() =
-  for i in 1 .. 1_000_000:
-    when defined(gcMarkAndSweep) or defined(boehmgc):
-      GC_fullcollect()
+  for i in 1 .. numIter:
+    when collectAlways: GC_fullcollect()
     var obj: TTestObj
     obj = makeObj()
-    if getOccupiedMem() > 300_000: quit("still a leak!")
+    let mem = getOccupiedMem()
+    when isDeterministic:
+      if i <= numIterStable:
+        memMax = mem
+        doAssert memMax <= 50_000 # adjust as needed
+      else:
+        # memory shouldn't increase after 1st few iterations
+        # on linux 386 it somehow takes 3 iters to converge
+        doAssert mem <= memMax
+    else:
+      if mem < memPrevious:
+        # a collection happened, it peaked at memPrevious
+        # echo (mem, memMin, memMax, numCollections, numIter, i) # for debugging
+        numCollections.inc
+        if numCollections <= numCycleStable:
+          # this is the 1st few collections, we update the min/max
+          doAssert memPrevious < 300_000 # adjust as needed
+          if memMin < mem: # `<` intentional; the valley may increase 
+            memMin = mem
+          if memMax < memPrevious:
+            memMax = memPrevious
+        else:
+          # after a collection, we always go back to same level
+          doAssert mem <= memMin, $(mem, memMin)
+
+      if numCollections >= numCycleStable:
+        # after a few cycles, the max stabilizes
+        doAssert mem <= memMax, $(mem, memMax)
+
+      memPrevious = mem
 
 inProc()
-echo "no leak: ", getOccupiedMem()
+let mem = getOccupiedMem()
+var msg = "no leak: "
+when isDeterministic:
+  msg.add $(mem, memMax)
+  echo msg
+else:
+  msg.add $(mem, memMin, memMax, numCollections, numIter)
+  echo msg
+  # make sure some collections did happen, otherwise the previous tests
+  # are meaningless
+  doAssert numCollections > 1000 # 3999 on local OSX; leaving some slack