Revert "fixes #22510 (#23100)"

This reverts commit d6bc8699b9.

lib/system/alloc.nim

@@ -93,6 +93,8 @@ type
     freeList: ptr FreeCell
     free: int            # how many bytes remain
     acc: int             # accumulator for small object allocation
+    when defined(gcDestructors):
+      sharedFreeList: ptr FreeCell # make no attempt at avoiding false sharing for now for this object field
     data {.align: MemAlign.}: UncheckedArray[byte]      # start of usable memory
 
   BigChunk = object of BaseChunk # not necessarily > PageSize!
@@ -107,9 +109,7 @@ type
   MemRegion = object
     when not defined(gcDestructors):
       minLargeObj, maxLargeObj: int
-    freeSmallChunks: array[0..max(1, SmallChunkSize div MemAlign-1), PSmallChunk]
-    when defined(gcDestructors):
-      sharedFreeLists: array[0..max(1, SmallChunkSize div MemAlign-1), ptr FreeCell]
+    freeSmallChunks: array[0..max(1,SmallChunkSize div MemAlign-1), PSmallChunk]
     flBitmap: uint32
     slBitmap: array[RealFli, uint32]
     matrix: array[RealFli, array[MaxSli, PBigChunk]]
@@ -775,10 +775,8 @@ when defined(gcDestructors):
     sysAssert c.next == nil, "c.next pointer must be nil"
     atomicPrepend a.sharedFreeListBigChunks, c
 
-  proc addToSharedFreeList(c: PSmallChunk; f: ptr FreeCell; size: int) {.inline.} =
-    atomicPrepend c.owner.sharedFreeLists[size], f
-
-  const MaxSteps = 20
+  proc addToSharedFreeList(c: PSmallChunk; f: ptr FreeCell) {.inline.} =
+    atomicPrepend c.sharedFreeList, f
 
   proc compensateCounters(a: var MemRegion; c: PSmallChunk; size: int) =
     # rawDealloc did NOT do the usual:
@@ -788,26 +786,30 @@ when defined(gcDestructors):
     # we split the list in order to achieve bounded response times.
     var it = c.freeList
     var x = 0
+    var maxIters = 20 # make it time-bounded
     while it != nil:
+      if maxIters == 0:
+        let rest = it.next.loada
+        if rest != nil:
+          it.next.storea nil
+          addToSharedFreeList(c, rest)
+        break
       inc x, size
-      let chunk = cast[PSmallChunk](pageAddr(it))
-      inc(chunk.free, x)
-      it = it.next
+      it = it.next.loada
+      dec maxIters
+    inc(c.free, x)
     dec(a.occ, x)
 
   proc freeDeferredObjects(a: var MemRegion; root: PBigChunk) =
     var it = root
-    var maxIters = MaxSteps # make it time-bounded
+    var maxIters = 20 # make it time-bounded
     while true:
-      let rest = it.next.loada
-      it.next.storea nil
-      deallocBigChunk(a, cast[PBigChunk](it))
       if maxIters == 0:
-        if rest != nil:
-          addToSharedFreeListBigChunks(a, rest)
-          sysAssert a.sharedFreeListBigChunks != nil, "re-enqueing failed"
+        let rest = it.next.loada
+        it.next.storea nil
+        addToSharedFreeListBigChunks(a, rest)
         break
-      it = rest
+      it = it.next.loada
       dec maxIters
       if it == nil: break
 
@@ -831,6 +833,8 @@ proc rawAlloc(a: var MemRegion, requestedSize: int): pointer =
       sysAssert c.size == PageSize, "rawAlloc 3"
       c.size = size
       c.acc = size
+      when defined(gcDestructors):
+        c.sharedFreeList = nil
       c.free = SmallChunkSize - smallChunkOverhead() - size
       sysAssert c.owner == addr(a), "rawAlloc: No owner set!"
       c.next = nil
@@ -847,11 +851,10 @@ proc rawAlloc(a: var MemRegion, requestedSize: int): pointer =
       when defined(gcDestructors):
         if c.freeList == nil:
           when hasThreadSupport:
-            # Steal the entire list from `sharedFreeList`:
-            c.freeList = atomicExchangeN(addr a.sharedFreeLists[s], nil, ATOMIC_RELAXED)
+            c.freeList = atomicExchangeN(addr c.sharedFreeList, nil, ATOMIC_RELAXED)
           else:
-            c.freeList = a.sharedFreeLists[s]
-            a.sharedFreeLists[s] = nil
+            c.freeList = c.sharedFreeList
+            c.sharedFreeList = nil
           compensateCounters(a, c, size)
       if c.freeList == nil:
         sysAssert(c.acc + smallChunkOverhead() + size <= SmallChunkSize,
@@ -918,7 +921,7 @@ proc rawDealloc(a: var MemRegion, p: pointer) =
   if isSmallChunk(c):
     # `p` is within a small chunk:
     var c = cast[PSmallChunk](c)
-    let s = c.size
+    var s = c.size
     #       ^ We might access thread foreign storage here.
     # The other thread cannot possibly free this block as it's still alive.
     var f = cast[ptr FreeCell](p)
@@ -952,7 +955,7 @@ proc rawDealloc(a: var MemRegion, p: pointer) =
           freeBigChunk(a, cast[PBigChunk](c))
     else:
       when defined(gcDestructors):
-        addToSharedFreeList(c, f, s div MemAlign)
+        addToSharedFreeList(c, f)
     sysAssert(((cast[int](p) and PageMask) - smallChunkOverhead()) %%
                s == 0, "rawDealloc 2")
   else:

tests/alloc/tmembug.nim

@@ -1,54 +0,0 @@
-discard """
-  joinable: false
-"""
-
-import std / [atomics, strutils, sequtils]
-
-type
-  BackendMessage* = object
-    field*: seq[int]
-
-var
-  chan1: Channel[BackendMessage]
-  chan2: Channel[BackendMessage]
-
-chan1.open()
-chan2.open()
-
-proc routeMessage*(msg: BackendMessage) =
-  discard chan2.trySend(msg)
-
-var
-  recv: Thread[void]
-  stopToken: Atomic[bool]
-
-proc recvMsg() =
-  while not stopToken.load(moRelaxed):
-    let resp = chan1.tryRecv()
-    if resp.dataAvailable:
-      routeMessage(resp.msg)
-      echo "child consumes ", formatSize getOccupiedMem()
-
-createThread[void](recv, recvMsg)
-
-const MESSAGE_COUNT = 100
-
-proc main() =
-  let msg: BackendMessage = BackendMessage(field: (0..500).toSeq())
-  for j in 0..0: #100:
-    echo "New iteration"
-
-    for _ in 1..MESSAGE_COUNT:
-      chan1.send(msg)
-    echo "After sending"
-
-    var counter = 0
-    while counter < MESSAGE_COUNT:
-      let resp = recv(chan2)
-      counter.inc
-    echo "After receiving ", formatSize getOccupiedMem()
-
-  stopToken.store true, moRelaxed
-  joinThreads(recv)
-
-main()

tests/alloc/tmembug2.nim

@@ -1,58 +0,0 @@
-discard """
-  disabled: "true"
-"""
-
-import std / [atomics, strutils, sequtils, isolation]
-
-import threading / channels
-
-type
-  BackendMessage* = object
-    field*: seq[int]
-
-const MESSAGE_COUNT = 100
-
-var
-  chan1 = newChan[BackendMessage](MESSAGE_COUNT*2)
-  chan2 = newChan[BackendMessage](MESSAGE_COUNT*2)
-
-#chan1.open()
-#chan2.open()
-
-proc routeMessage*(msg: BackendMessage) =
-  var m = isolate(msg)
-  discard chan2.trySend(m)
-
-var
-  thr: Thread[void]
-  stopToken: Atomic[bool]
-
-proc recvMsg() =
-  while not stopToken.load(moRelaxed):
-    var resp: BackendMessage
-    if chan1.tryRecv(resp):
-      #if resp.dataAvailable:
-      routeMessage(resp)
-      echo "child consumes ", formatSize getOccupiedMem()
-
-createThread[void](thr, recvMsg)
-
-proc main() =
-  let msg: BackendMessage = BackendMessage(field: (0..5).toSeq())
-  for j in 0..100:
-    echo "New iteration"
-
-    for _ in 1..MESSAGE_COUNT:
-      chan1.send(msg)
-    echo "After sending"
-
-    var counter = 0
-    while counter < MESSAGE_COUNT:
-      let resp = recv(chan2)
-      counter.inc
-    echo "After receiving ", formatSize getOccupiedMem()
-
-  stopToken.store true, moRelaxed
-  joinThreads(thr)
-
-main()

tests/threads/tmembug.nim

@@ -1,51 +0,0 @@
-
-import std / [atomics, strutils, sequtils]
-
-type
-  BackendMessage* = object
-    field*: seq[int]
-
-var
-  chan1: Channel[BackendMessage]
-  chan2: Channel[BackendMessage]
-
-chan1.open()
-chan2.open()
-
-proc routeMessage*(msg: BackendMessage) =
-  discard chan2.trySend(msg)
-
-var
-  recv: Thread[void]
-  stopToken: Atomic[bool]
-
-proc recvMsg() =
-  while not stopToken.load(moRelaxed):
-    let resp = chan1.tryRecv()
-    if resp.dataAvailable:
-      routeMessage(resp.msg)
-      echo "child consumes ", formatSize getOccupiedMem()
-
-createThread[void](recv, recvMsg)
-
-const MESSAGE_COUNT = 100
-
-proc main() =
-  let msg: BackendMessage = BackendMessage(field: (0..500).toSeq())
-  for j in 0..0: #100:
-    echo "New iteration"
-
-    for _ in 1..MESSAGE_COUNT:
-      chan1.send(msg)
-    echo "After sending"
-
-    var counter = 0
-    while counter < MESSAGE_COUNT:
-      let resp = recv(chan2)
-      counter.inc
-    echo "After receiving ", formatSize getOccupiedMem()
-
-  stopToken.store true, moRelaxed
-  joinThreads(recv)
-
-main()