Fix memory leak

monix-eval/shared/src/main/scala/monix/eval/internal/TaskBracket.scala

@@ -263,10 +263,10 @@ private[monix] object TaskBracket {
     }
 
     private final def makeUncancelable(task: Task[B]): Task[B] = {
-      // NOTE: the "restore" part of this is `null` because we don't need to restore
-      // the original connection. The original connection gets restored automatically
-      // via how "TaskRestartCallback" works. This is risky!
-      ContextSwitch(task, withConnectionUncancelable, null)
+      // Unregistering cancel token, otherwise we can have a memory leak;
+      // N.B. conn.pop() happens after the evaluation of `release`, because
+      // otherwise we might have a conflict with the auto-cancellation logic
+      ContextSwitch(task, withConnectionUncancelable, disableUncancelableAndPop)
     }
   }
 
@@ -282,4 +282,10 @@ private[monix] object TaskBracket {
 
   private[this] val withConnectionUncancelable: Context => Context =
     _.withConnection(TaskConnection.uncancelable)
+
+  private[this] val disableUncancelableAndPop: (Any, Throwable, Context, Context) => Context =
+    (_, _, old, _) => {
+      old.connection.pop()
+      old
+    }
 }

monix-eval/shared/src/main/scala/monix/eval/internal/TaskConnection.scala

@@ -56,7 +56,7 @@ private[eval] sealed abstract class TaskConnection extends CancelableF[Task] {
 
   /**
     * Pushes a cancelable token on the stack, to be
-    * popped or canceled later in FIFO order.
+    * popped or canceled later in LIFO order.
     *
     * The function needs a [[monix.execution.Scheduler Scheduler]]
     * to work because in case the connection was already cancelled,
@@ -66,7 +66,7 @@ private[eval] sealed abstract class TaskConnection extends CancelableF[Task] {
 
   /**
     * Pushes a [[monix.execution.Cancelable]] on the stack, to be
-    * popped or canceled later in FIFO order.
+    * popped or canceled later in LIFO order.
     *
     * The function needs a [[monix.execution.Scheduler Scheduler]]
     * to work because in case the connection was already cancelled,
@@ -76,7 +76,7 @@ private[eval] sealed abstract class TaskConnection extends CancelableF[Task] {
 
   /**
     * Pushes a [[monix.catnap.CancelableF]] on the stack, to be
-    * popped or canceled later in FIFO order.
+    * popped or canceled later in LIFO order.
     *
     * The function needs a [[monix.execution.Scheduler Scheduler]]
     * to work because in case the connection was already cancelled,
@@ -94,7 +94,7 @@ private[eval] sealed abstract class TaskConnection extends CancelableF[Task] {
   def pushConnections(seq: CancelableF[Task]*)(implicit s: Scheduler): Unit
 
   /**
-    * Removes a cancelable reference from the stack in FIFO order.
+    * Removes a cancelable reference from the stack in LIFO order.
     *
     * @return the cancelable reference that was removed.
     */