Merge eff04d8efa57f37a9ba156e0ffe3b6baf5cbe552 into 61ff2594d3e204b2ef597b17207094ada2fd7c5c

src/apatheia/jobs.nim

@@ -50,6 +50,11 @@ type
 template toOpenArray*[T](arr: OpenArrayHolder[T]): auto =
   system.toOpenArray(arr.data, 0, arr.size)
 
+proc toArrayHolder*[T](data: seq[T]): OpenArrayHolder[T] =
+    OpenArrayHolder[T](
+      data: cast[ptr UncheckedArray[T]](unsafeAddr(data[0])), size: data.len()
+    )
+
 func jobId*[T](fut: Future[T]): JobId =
   JobId fut.id()
 
@@ -93,9 +98,7 @@ template checkJobArgs*[T](exp: seq[T], fut: untyped): OpenArrayHolder[T] =
   when T is SupportedSeqTypes:
     let rval = SeqRetainer[T](data: exp)
     retainMemory(fut.jobId(), rval)
-    let expPtr = OpenArrayHolder[T](
-      data: cast[ptr UncheckedArray[T]](unsafeAddr(rval.data[0])), size: rval.data.len()
-    )
+    let expPtr = toArrayHolder(rval.data)
     expPtr
   else:
     {.error: "unsupported sequence type for job argument: " & $typeof(seq[T]).}
@@ -103,9 +106,7 @@ template checkJobArgs*[T](exp: seq[T], fut: untyped): OpenArrayHolder[T] =
 template checkJobArgs*(exp: string, fut: untyped): OpenArrayHolder[char] =
     let rval = StrRetainer(data: exp)
     retainMemory(fut.jobId(), rval)
-    let expPtr = OpenArrayHolder[char](
-      data: cast[ptr UncheckedArray[char]](unsafeAddr(rval.data[0])), size: rval.data.len()
-    )
+    let expPtr = toArrayHolder(rval.data)
     expPtr
 
 template checkJobArgs*(exp: typed, fut: untyped): auto =

tests/exCursor.nim

@@ -0,0 +1 @@
+

tests/exampleGcFailures/config.nims

@@ -0,0 +1,2 @@
+--threads:on
+--mm:refc

tests/exampleGcFailures/exFailure.nim

@@ -0,0 +1,69 @@
+import std/os
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## This example mocks up a sequence and uses
+## a finalizer and GC_fullCollect to more
+## deterministically create a memory error.
+## 
+## see `exFailureSeq.nim` for a probablisitc based
+## example using a real seq object.
+## 
+
+type
+  Seq*[T] = object
+    data*: ptr UncheckedArray[T]
+    size*: int
+
+  DataObj = ref object
+    mockSeq: Seq[char]
+
+template toOpenArray*[T](arr: Seq[T]): auto =
+  system.toOpenArray(arr.data, 0, arr.size)
+
+proc worker(data: ptr Seq[char], sig: ThreadSignalPtr) =
+  os.sleep(1_000)
+  echo "running worker: "
+  assert data[].data != nil
+  echo "worker: ", data[].toOpenArray()
+  discard sig.fireSync()
+
+proc finalizer(obj: DataObj) =
+  echo "finalize DataObj and freeing mockSeq"
+  obj.mockSeq.data.dealloc()
+  obj.mockSeq.data = nil
+
+proc initMockSeq(msg: string): Seq[char] =
+  result.data = cast[ptr UncheckedArray[char]](alloc0(13))
+  for i, c in msg:
+    result.data[i] = c
+  result.size = 12
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj: DataObj
+  obj.new(finalizer)
+  obj.mockSeq = initMockSeq("hello world!")
+
+  echo "spawn worker"
+  tp.spawn worker(addr obj.mockSeq, sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  await wait(sig)
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    try:
+      await runTest(tp, sig).wait(100.milliseconds)
+    except AsyncTimeoutError:
+      echo "Run GC"
+      GC_fullCollect()
+      os.sleep(2_000)
+      echo "Done"

tests/exampleGcFailures/exFailure2.nim

@@ -0,0 +1,81 @@
+import std/os
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## This example mocks up a sequence and uses
+## a finalizer and GC_fullCollect to more
+## deterministically create a memory error.
+## 
+## see `exFailureSeq.nim` for a probablisitc based
+## example using a real seq object.
+## 
+
+type
+  Seq*[T] = object
+    data*: ptr UncheckedArray[T]
+    size*: int
+
+  DataObj = ref object
+    mockSeq: Seq[char]
+
+template toOpenArray*[T](arr: Seq[T]): auto =
+  system.toOpenArray(arr.data, 0, arr.size)
+
+proc worker(data: ptr Seq[char], sig: ThreadSignalPtr) =
+  os.sleep(5_000)
+  echo "running worker: "
+  assert data[].data != nil
+  echo "worker: ", data[].toOpenArray()
+  discard sig.fireSync()
+
+proc finalizer(obj: DataObj) =
+  echo "finalize DataObj and freeing mockSeq"
+  obj.mockSeq.data.dealloc()
+  obj.mockSeq.data = nil
+
+proc initMockSeq(msg: string): Seq[char] =
+  result.data = cast[ptr UncheckedArray[char]](alloc0(13))
+  for i, c in msg:
+    result.data[i] = c
+  result.size = 12
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj: DataObj
+  obj.new(finalizer)
+  obj.mockSeq = initMockSeq("hello world!")
+
+  echo "spawn worker"
+  tp.spawn worker(addr obj.mockSeq, sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  try:
+    await wait(sig)
+    echo "runTest got sig"
+  finally:
+    echo "runTest done"
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc doFail() {.async.} =
+  await sleepAsync(10.milliseconds)
+  raise newException(CatchableError, "error")
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    try:
+      await allFutures(
+        runTest(tp, sig),
+        doFail(),
+      )
+    except Defect:
+      echo "Errored out"
+    finally:
+      echo "Run GC"
+      GC_fullCollect()
+      os.sleep(2_000)

tests/exampleGcFailures/exFailureNoGcCollect.nim

@@ -0,0 +1,63 @@
+import std/os
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+type
+  Seq*[T] = object
+    data*: ptr UncheckedArray[T]
+    size*: int
+
+  DataObj = ref object
+    mockSeq: Seq[char]
+
+template toOpenArray*[T](arr: Seq[T]): auto =
+  system.toOpenArray(arr.data, 0, arr.size)
+
+proc worker(data: ptr Seq[char], sig: ThreadSignalPtr) =
+  os.sleep(4_000)
+  echo "running worker: "
+  assert data[].data != nil
+  echo "worker: ", data[].toOpenArray()
+  discard sig.fireSync()
+
+proc finalizer(obj: DataObj) =
+  echo "finalize DataObj and freeing mockSeq"
+  obj.mockSeq.data.dealloc()
+  obj.mockSeq.data = nil
+
+proc initMockSeq(msg: string): Seq[char] =
+  result.data = cast[ptr UncheckedArray[char]](alloc0(13))
+  for i, c in msg:
+    result.data[i] = c
+  result.size = 12
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj: DataObj
+  obj.new(finalizer)
+  obj.mockSeq = initMockSeq("hello world!")
+
+  echo "spawn worker"
+  tp.spawn worker(addr obj.mockSeq, sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  await wait(sig).wait(100.milliseconds)
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  for i in 1..2_000:
+    try:
+      await runTest(tp, sig)
+      os.sleep(200)
+    except AsyncTimeoutError:
+      echo "looping..."
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)

tests/exampleGcFailures/exFailureSeq.nim

@@ -0,0 +1,68 @@
+import std/os
+import std/sequtils
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## create a probablistically likely failure of 
+## using sequence memory from another thread
+## with refc. 
+## 
+## However, unlike `exFailure.nim`, this can take
+## a while to run.
+## 
+## It may not always produce an error either, but
+## generally does so in a few seconds of running.
+## 
+
+type
+  SeqDataPtr*[T] = object
+    data*: ptr UncheckedArray[T]
+    size*: int
+
+template toOpenArray*[T](arr: SeqDataPtr[T]): auto =
+  system.toOpenArray(arr.data, 0, arr.size)
+
+proc toSeqDataPtr*[T](data: seq[T]): SeqDataPtr[T] =
+    SeqDataPtr[T](
+      data: cast[ptr UncheckedArray[T]](unsafeAddr(data[0])), size: data.len()
+    )
+
+proc worker(data: SeqDataPtr[char], sig: ThreadSignalPtr) =
+  os.sleep(10)
+  echo "running worker: "
+  echo "worker: ", data.toOpenArray()
+  for i, c in data.toOpenArray():
+    data.data[i] = char(c.uint8 + 10)
+  discard sig.fireSync()
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj = "hello world!".toSeq()
+
+  # echo "spawn worker"
+  tp.spawn worker(obj.toSeqDataPtr(), sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  await wait(sig).wait(1.milliseconds)
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  for i in 1..30_000:
+    try:
+      await runTest(tp, sig)
+    except AsyncTimeoutError:
+      # os.sleep(1)
+      # echo "looping..."
+      # GC_fullCollect()
+      discard
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)
+    os.sleep(10_000)

tests/exampleGcFailures/exFailureSeqSeqCursor.nim

@@ -0,0 +1,66 @@
+import std/os
+import std/sequtils
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## create a probablistically likely failure of 
+## using sequence memory from another thread
+## with refc. 
+## 
+## However, unlike `exFailure.nim`, this can take
+## a while to run.
+## 
+## It may not always produce an error either, but
+## generally does so in a few seconds of running.
+## 
+
+type
+  SeqCursor* = object
+    data* {.cursor.}: seq[seq[char]]
+
+proc worker(data: SeqCursor, sig: ThreadSignalPtr) =
+  os.sleep(10)
+  echo "running worker: "
+  echo "worker: ", data.data
+  echo "worker:addr: ", cast[pointer](data.data).repr
+  # for i, d in data.data:
+  #   for j, c in d:
+  #     data.data[i][j] = char(c.uint8 + 10)
+  discard sig.fireSync()
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj1 = "hello world!".toSeq()
+  var obj2 = "goodbye denver!".toSeq()
+  var data = @[obj1, obj2]
+  var cur = SeqCursor(data: data)
+
+  # echo "spawn worker"
+  tp.spawn worker(cur, sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  await wait(sig)
+  echo "data:addr: ", data.addr.pointer.repr
+  echo "data:cursor:addr: ", cast[pointer](cur.data).repr
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  for i in 1..1:
+    try:
+      await runTest(tp, sig)
+    except AsyncTimeoutError:
+      # os.sleep(1)
+      # echo "looping..."
+      # GC_fullCollect()
+      discard
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)
+    # os.sleep(10_000)

tests/exampleGcFailures/exFailureWrapSuccess.nim

@@ -0,0 +1,84 @@
+import std/os
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## This example mocks up a sequence and uses
+## a finalizer and GC_fullCollect to more
+## deterministically create a memory error.
+## 
+## This variant tries using `allFutures` to prevent
+## cancelation of the thread-future. 
+## 
+## It keeps the future from finishing before
+## the task runs. However, it doesn't appear to be
+## triggering the finalizer for the MockSeq.
+## 
+
+type
+  Seq*[T] = object
+    data*: ptr UncheckedArray[T]
+    size*: int
+
+  DataObj = ref object
+    mockSeq: Seq[char]
+
+template toOpenArray*[T](arr: Seq[T]): auto =
+  system.toOpenArray(arr.data, 0, arr.size)
+
+proc worker(data: ptr Seq[char], sig: ThreadSignalPtr) =
+  os.sleep(1_000)
+  echo "running worker: "
+  assert data[].data != nil
+  echo "worker: ", data[].toOpenArray()
+  discard sig.fireSync()
+
+proc finalizer(obj: DataObj) =
+  echo "finalize DataObj and freeing mockSeq"
+  obj.mockSeq.data.dealloc()
+  obj.mockSeq.data = nil
+
+proc initMockSeq(msg: string): Seq[char] =
+  result.data = cast[ptr UncheckedArray[char]](alloc0(13))
+  for i, c in msg:
+    result.data[i] = c
+  result.size = 12
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj: DataObj
+  obj.new(finalizer)
+  obj.mockSeq = initMockSeq("hello world!")
+
+  echo "spawn worker"
+  tp.spawn worker(addr obj.mockSeq, sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  try:
+    await wait(sig)
+  finally:
+    echo "finishing runTest"
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc runTestWrap(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  await runTest(tp, sig).allFutures().wait(100.milliseconds)
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    try:
+      await runTestWrap(tp, sig)
+    except AsyncTimeoutError:
+      echo "Run GC"
+      GC_fullCollect()
+      os.sleep(2_000)
+      echo "Done"
+    os.sleep(10_000)
+    GC_fullCollect()
+  
+  teardown:
+    GC_fullCollect()

tests/exampleGcFailures/exNoFailureNoGcCollectSeq.nim

@@ -0,0 +1,39 @@
+import std/os
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+proc worker(data: string, sig: ThreadSignalPtr) =
+  os.sleep(4_000)
+  echo "running worker: "
+  echo "worker: ", data
+  discard sig.fireSync()
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj = "hello world!"
+  # obj.shallow()
+
+  echo "spawn worker"
+  tp.spawn worker(obj, sig)
+
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  await wait(sig).wait(100.milliseconds)
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  for i in 1..2_000:
+    try:
+      await runTest(tp, sig)
+      os.sleep(200)
+    except AsyncTimeoutError:
+      echo "looping..."
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)

tests/exampleGcFailures/exNoFailureNoGcCollectSeqDestroy.nim

@@ -0,0 +1,48 @@
+import std/os
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+type
+  Test* = object
+    count*: int
+
+proc `=destroy`*(obj: var Test) =
+  echo "destroy count: ", obj.count, " thread: ", getThreadId()
+
+proc worker(data: seq[Test], sig: ThreadSignalPtr) =
+  os.sleep(40)
+  echo "running worker: ", getThreadId()
+  echo "worker: ", data
+  discard sig.fireSync()
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  ## init
+  var obj = @[Test(count: 1), Test(count: 2)]
+
+  echo "spawn worker"
+  tp.spawn worker(obj, sig)
+
+  obj[0].count = 10
+  obj[1].count = 20
+  ## adding fut.wait(100.milliseconds) creates memory issue
+  await wait(sig)
+  ## just doing the wait is fine:
+  # await wait(sig)
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  for i in 1..1:
+    try:
+      echo "\n\nrunning main: ", getThreadId()
+      await runTest(tp, sig)
+      os.sleep(200)
+    except AsyncTimeoutError:
+      echo "looping..."
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 2) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)

tests/exampleGcFailures/exNoFailurePtrSeqSeq.nim

@@ -0,0 +1,60 @@
+import std/os
+import std/sequtils
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## create a probablistically likely failure of 
+## using sequence memory from another thread
+## with refc. 
+## 
+## However, unlike `exFailure.nim`, this can take
+## a while to run.
+## 
+## It may not always produce an error either, but
+## generally does so in a few seconds of running.
+## 
+
+proc worker(data: ptr seq[seq[char]], sig: ThreadSignalPtr) =
+  # os.sleep(100)
+  echo "running worker: "
+  echo "worker: ", data.pointer.repr
+  echo "worker: ", data[]
+  # for i, d in data:
+  #   for j, c in d:
+  #     data[i][j] = char(c.uint8 + 10)
+  GC_fullCollect()
+  discard sig.fireSync()
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr, i: int) {.async.} =
+  ## init
+  # await sleepAsync(10.milliseconds)
+  var obj1 = ("hello world! " & $i).toSeq()
+  var obj2 = "goodbye denver!".toSeq()
+  var data = @[obj1, obj2]
+
+  # echo "spawn worker"
+  tp.spawn worker(addr data, sig)
+
+  await wait(sig)
+  echo "data: ", data.addr.pointer.repr
+  echo "data: ", data
+  echo ""
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  var futs = newSeq[Future[void]]()
+  for i in 1..1:
+    let f = runTest(tp, sig, i)
+    # futs.add f
+    await f
+    GC_fullCollect()
+  await allFutures(futs)
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 4) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)
+    # os.sleep(10_000)

tests/exampleGcFailures/exNoFailureSeqSeq.nim

@@ -0,0 +1,60 @@
+import std/os
+import std/sequtils
+import chronos
+import chronos/threadsync
+import chronos/unittest2/asynctests
+import taskpools
+
+## create a probablistically likely failure of 
+## using sequence memory from another thread
+## with refc. 
+## 
+## However, unlike `exFailure.nim`, this can take
+## a while to run.
+## 
+## It may not always produce an error either, but
+## generally does so in a few seconds of running.
+## 
+
+proc worker(data: seq[seq[char]], sig: ThreadSignalPtr) =
+  os.sleep(1_000)
+  echo "running worker: "
+  echo "worker: ", data.unsafeAddr.pointer.repr
+  echo "worker: ", data
+  # for i, d in data:
+  #   for j, c in d:
+  #     data[i][j] = char(c.uint8 + 10)
+  GC_fullCollect()
+  discard sig.fireSync()
+
+proc runTest(tp: TaskPool, sig: ThreadSignalPtr, i: int) {.async.} =
+  ## init
+  # await sleepAsync(10.milliseconds)
+  var obj1 = ("hello world! " & $i).toSeq()
+  var obj2 = "goodbye denver!".toSeq()
+  var data = @[obj1, obj2]
+
+  # echo "spawn worker"
+  tp.spawn worker(data, sig)
+
+  await wait(sig)
+  echo "data: ", data.addr.pointer.repr
+  echo "data: ", data
+  echo ""
+
+proc runTests(tp: TaskPool, sig: ThreadSignalPtr) {.async.} =
+  var futs = newSeq[Future[void]]()
+  for i in 1..10_000:
+    let f = runTest(tp, sig, i).wait(100.milliseconds)
+    # futs.add f
+    await f
+    GC_fullCollect()
+  await allFutures(futs)
+
+suite "async tests":
+  var tp = Taskpool.new(num_threads = 4) # Default to the number of hardware threads.
+  let sig = ThreadSignalPtr.new().get()
+
+  asyncTest "test":
+    await runTests(tp, sig)
+    # os.sleep(10_000)

tests/exampleGcFailures/example.nim

@@ -0,0 +1,214 @@
+while true:
+  block :stateLoop:
+    try:
+      var
+        :tmpD
+        :tmpD_1
+        :tmpD_2
+        :tmpD_3
+      closureIterSetupExc(:envP.`:curExc1`)
+      goto :envP.`:state`6
+      state 0:
+      template result(): auto {.used.} =
+        {.fatal: "You should not reference the `result` variable inside" &
+            " a void async proc".}
+
+      var :envP.closureSucceeded25 = true
+      :envP.`:state` = 1
+      break :stateLoop
+      state 1:
+      var :envP.obj117 =
+        type
+          OutType`gensym13 = typeof(items("hello world! " & $i))
+        block :tmp:
+          :tmpD =
+            let :envP.`:tmp5` = `&`("hello world! ", $:envP.`:up`.i1)
+            template s2_838861096(): untyped =
+              :tmp_1
+            
+            var :envP.i`gensym1310 = 0
+            var :envP.result`gensym139 = newSeq(
+                chckRange(len(:envP.`:tmp5`), 0, 9223372036854775807))
+            block :tmp_2:
+              var :envP.it`gensym138
+              var :envP.i6 = 0
+              let :envP.L7 = len(:envP.`:tmp5`)
+              block :tmp_3:
+                while :envP.i6 < :envP.L7:
+                  :envP.it`gensym138 = :envP.`:tmp5`[:envP.i6]
+                  :envP.result`gensym139[:envP.i`gensym1310] = :envP.it`gensym138
+                  :envP.i`gensym1310 += 1
+                  inc(:envP.i6, 1)
+                  const
+                    loc`gensym22 = (filename: "/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim",
+                      line: 258, column: 10)
+                    ploc`gensym22 = "/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim(258, 11)"
+                  bind instantiationInfo
+                  mixin failedAssertImpl
+                  {.line: (filename: "/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim",
+                           line: 258, column: 10).}:
+                    if not (len(:envP.`:tmp5`) == :envP.L7):
+                      failedAssertImpl("/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim(258, 11) `len(a) == L` the length of the string changed while iterating over it")
+            :envP.result`gensym139
+          :tmpD
+      var :envP.obj218 =
+        type
+          OutType`gensym20 = typeof(items("goodbye denver!"))
+        block :tmp_4:
+          :tmpD_1 =
+            let :envP.`:tmp11` = "goodbye denver!"
+            template s2_838861153(): untyped =
+              :tmp_5
+            
+            var :envP.i`gensym2016 = 0
+            var :envP.result`gensym2015 = newSeq(
+                chckRange(len(:envP.`:tmp11`), 0, 9223372036854775807))
+            block :tmp_6:
+              var :envP.it`gensym2014
+              var :envP.i12 = 0
+              let :envP.L13 = len(:envP.`:tmp11`)
+              block :tmp_7:
+                while :envP.i12 < :envP.L13:
+                  :envP.it`gensym2014 = :envP.`:tmp11`[:envP.i12]
+                  :envP.result`gensym2015[:envP.i`gensym2016] = :envP.it`gensym2014
+                  :envP.i`gensym2016 += 1
+                  inc(:envP.i12, 1)
+                  const
+                    loc`gensym22 = (filename: "/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim",
+                      line: 258, column: 10)
+                    ploc`gensym22 = "/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim(258, 11)"
+                  bind instantiationInfo
+                  mixin failedAssertImpl
+                  {.line: (filename: "/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim",
+                           line: 258, column: 10).}:
+                    if not (len(:envP.`:tmp11`) == :envP.L13):
+                      failedAssertImpl("/Users/elcritch/.asdf/installs/nim/1.6.18/lib/system/iterators.nim(258, 11) `len(a) == L` the length of the string changed while iterating over it")
+            :envP.result`gensym2015
+          :tmpD_1
+      var :envP.data20 = @[
+        :tmpD_2 = :envP.obj117
+        :tmpD_2,
+        :tmpD_3 = :envP.obj218
+        :tmpD_3]
+      block :tmp_8:
+        var
+          :tmpD_4
+          :tmpD_5
+          :tmpD_6
+          :tmpD_7
+        let :envP.taskNode23 = new(TaskNode, workerContext.currentTask) do:
+          type
+            ScratchObj = object
+              data: seq[seq[char]]
+              sig: ThreadSignalPtr
+
+          let :envP.scratch19 = cast[ptr ScratchObj](c_calloc(1'u, 16'u))
+          if isNil(:envP.scratch19):
+            raise
+              (ref OutOfMemDefect)(msg: "Could not allocate memory", parent: nil)
+          block :tmp_9:
+            var
+              :tmpD_8
+              :tmpD_9
+            `=sink`(:envP.isoTemp21, isolate do:
+              :tmpD_8 = :envP.data20
+              :tmpD_8)
+            :envP.scratch19.data = extract(:envP.isoTemp21)
+            `=sink_1`(:envP.isoTemp22, isolate do:
+              :tmpD_9 = :envP.`:up`.sig2
+              :tmpD_9)
+            :envP.scratch19.sig = extract_1(:envP.isoTemp22)
+          proc worker_838861197(args`gensym27: pointer) {.gcsafe, nimcall,
+              raises: [].} =
+            let objTemp = cast[ptr ScratchObj](args`gensym27)
+            let data_1 = objTemp.data
+            let sig_1 = objTemp.sig
+            worker(data_1, sig_1)
+
+          proc destroyScratch_838861198(args`gensym27_1: pointer) {.gcsafe,
+              nimcall, raises: [].} =
+            let obj = cast[ptr ScratchObj](args`gensym27_1)
+            `=destroy`(obj[])
+
+          Task(callback:
+            :tmpD_4 = worker_1
+            :tmpD_4, args:
+            :tmpD_5 = :envP.scratch19
+            :tmpD_5, destroy:
+            :tmpD_6 = destroyScratch
+            :tmpD_6)
+        schedule(workerContext):
+          :tmpD_7 = :envP.taskNode23
+          :tmpD_7
+      chronosInternalRetFuture.internalChild = FutureBase(wait(:envP.`:up`.sig2))
+      :envP.`:state` = 4
+      return chronosInternalRetFuture.internalChild
+      state 2:
+      :envP.`:curExc1` = nil
+      if of(getCurrentException(), CancelledError):
+        :envP.closureSucceeded25 = false
+        cancelAndSchedule(FutureBase(cast[Future[void]](chronosInternalRetFuture)),
+                          srcLocImpl("", "exNoFailureSeqSeq.nim", 43))
+      elif of(getCurrentException(), CatchableError):
+        let :envP.exc26 = getCurrentException()
+        :envP.closureSucceeded25 = false
+        failImpl(FutureBase(cast[Future[void]](chronosInternalRetFuture)),
+                 :envP.exc26, srcLocImpl("", "exNoFailureSeqSeq.nim", 43))
+      elif of(getCurrentException(), Defect):
+        var :tmpD_10
+        let :envP.exc27 = getCurrentException()
+        :envP.closureSucceeded25 = false
+        raise
+          :tmpD_10 = :envP.exc27
+          :tmpD_10
+      else:
+        :envP.`:unrollFinally3` = true
+        :envP.`:curExc1` = getCurrentException()
+        :envP.`:state` = 3
+        break :stateLoop
+      :envP.`:state` = 3
+      break :stateLoop
+      state 3:
+      if :envP.closureSucceeded25:
+        complete(cast[Future[void]](chronosInternalRetFuture),
+                 srcLocImpl("", "exNoFailureSeqSeq.nim", 43))
+      if :envP.`:unrollFinally3`:
+        if `==`(:envP.`:curExc1`, nil):
+          :envP.`:state` = -1
+          return result = :envP.`:tmpResult2`
+        else:
+          var :tmpD_11
+          closureIterSetupExc(nil)
+          raise
+            :tmpD_11 = :envP.`:curExc1`
+            :tmpD_11
+      :envP.`:state` = 6
+      break :stateLoop
+      state 4:
+      {.cast(raises: [AsyncError, CancelledError]).}:
+        if isNil(cast[type(wait(sig_2))](chronosInternalRetFuture.internalChild).internalError):
+          discard
+         else:
+          var :tmpD_12
+          raise
+            :tmpD_12 = cast[type(wait(sig_2))](chronosInternalRetFuture.internalChild).internalError
+            :tmpD_12
+      :envP.`:state` = 5
+      break :stateLoop
+      state 5:
+      echo ["data: ", repr(pointer(addr(:envP.data20)))]
+      echo ["data: ", `$_1`(:envP.data20)]
+      echo [""]
+      :envP.`:state` = 3
+      break :stateLoop
+      state 6:
+      :envP.`:state` = -1
+      break :stateLoop
+    except:
+      :envP.`:state` = [0, -2, 3, 0, -2, -2, 0][:envP.`:state`]
+      if `==`(:envP.`:state`, 0):
+        raise
+      :envP.`:unrollFinally3` = `<`(0, :envP.`:state`)
+      if `<`(:envP.`:state`, 0):
+        :envP.`:state` = `-`(:envP.`:state`)
+      :envP.`:curExc1` = getCurrentException()

tests/exampleGcFailures/test.nim

@@ -0,0 +1,25 @@
+
+when false:
+  type AnObject* = object of RootObj
+    value*: int
+
+  proc mutate(a: sink AnObject) =
+    a.value = 1
+
+  var obj = AnObject(value: 42)
+  mutate(obj)
+  doAssert obj.value == 42
+
+else:
+  type AnObject = object of RootObj
+    value*: int
+
+  proc `=destroy`(x: var AnObject) = 
+    echo "DEST"
+
+  proc mutate(a: sink AnObject) =
+    a.value = 1
+
+  var obj = AnObject(value: 42)
+  mutate(obj)
+  doAssert obj.value == 42