ORC: make rootsThreshold thread local [backport]

lib/system/orc.nim

@@ -350,7 +350,7 @@ const
 when defined(nimStressOrc):
   const rootsThreshold = 10 # broken with -d:nimStressOrc: 10 and for havlak iterations 1..8
 else:
-  var rootsThreshold = defaultThreshold
+  var rootsThreshold {.threadvar.}: int
 
 proc partialCollect(lowMark: int) =
   when false:
@@ -392,13 +392,13 @@ proc collectCycles() =
     # of the cycle collector's effectiveness:
     # we're effective when we collected 50% or more of the nodes
     # we touched. If we're effective, we can reset the threshold:
-    if j.keepThreshold and rootsThreshold <= defaultThreshold:
+    if j.keepThreshold and rootsThreshold <= 0:
       discard
     elif j.freed * 2 >= j.touched:
       when not defined(nimFixedOrc):
         rootsThreshold = max(rootsThreshold div 3 * 2, 16)
       else:
-        rootsThreshold = defaultThreshold
+        rootsThreshold = 0
       #cfprintf(cstderr, "[collectCycles] freed %ld, touched %ld new threshold %ld\n", j.freed, j.touched, rootsThreshold)
     elif rootsThreshold < high(int) div 4:
       rootsThreshold = rootsThreshold * 3 div 2
@@ -411,7 +411,7 @@ proc registerCycle(s: Cell; desc: PNimTypeV2) =
   if roots.d == nil: init(roots)
   add(roots, s, desc)
 
-  if roots.len >= rootsThreshold:
+  if roots.len >= rootsThreshold+defaultThreshold:
     collectCycles()
   when logOrc:
     writeCell("[added root]", s, desc)
@@ -427,7 +427,7 @@ proc GC_enableOrc*() =
   ## Enables the cycle collector subsystem of `--gc:orc`. This is a `--gc:orc`
   ## specific API. Check with `when defined(gcOrc)` for its existence.
   when not defined(nimStressOrc):
-    rootsThreshold = defaultThreshold
+    rootsThreshold = 0
 
 proc GC_disableOrc*() =
   ## Disables the cycle collector subsystem of `--gc:orc`. This is a `--gc:orc`

tests/arc/tasyncleak.nim

@@ -1,5 +1,5 @@
 discard """
-  outputsub: "(allocCount: 4302, deallocCount: 4300)"
+  outputsub: "(allocCount: 4050, deallocCount: 4048)"
   cmd: "nim c --gc:orc -d:nimAllocStats $file"
 """
 

tests/arc/topt_no_cursor.nim

@@ -1,6 +1,6 @@
 discard """
   nimoutFull: true
-  cmd: '''nim c -r --warnings:off --hints:off --gc:arc --expandArc:newTarget --expandArc:delete --expandArc:p1 --expandArc:tt --hint:Performance:off --assertions:off --expandArc:extractConfig --expandArc:mergeShadowScope --expandArc:check $file'''
+  cmd: '''nim c -r --warnings:off --hints:off --mm:arc --expandArc:newTarget --expandArc:delete --expandArc:p1 --expandArc:tt --hint:Performance:off --assertions:off --expandArc:extractConfig --expandArc:mergeShadowScope --expandArc:check $file'''
   nimout: '''
 --expandArc: newTarget