scala · paulp · May 5, 2012 · Jan 22, 2012
diff --git a/src/library/scala/util/parsing/combinator/Parsers.scala b/src/library/scala/util/parsing/combinator/Parsers.scala
@@ -12,6 +12,7 @@ import scala.util.parsing.input._
 import scala.collection.mutable.ListBuffer
 import scala.annotation.tailrec
 import annotation.migration
+import scala.util.DynamicVariable
 
 // TODO: better error handling (labelling like parsec's <?>)
 
@@ -153,13 +154,14 @@ trait Parsers {
     val successful = true
   }
 
-  var lastNoSuccess: NoSuccess = null
+  private lazy val lastNoSuccess = new DynamicVariable[Option[NoSuccess]](None)
 
   /** A common super-class for unsuccessful parse results. */
   sealed abstract class NoSuccess(val msg: String, override val next: Input) extends ParseResult[Nothing] { // when we don't care about the difference between Failure and Error
     val successful = false
-    if (!(lastNoSuccess != null && next.pos < lastNoSuccess.next.pos))
-      lastNoSuccess = this
+
+    if (lastNoSuccess.value map { v => !(next.pos < v.next.pos) } getOrElse true)
+      lastNoSuccess.value = Some(this)
 
     def map[U](f: Nothing => U) = this
     def mapPartial[U](f: PartialFunction[Nothing, U], error: Nothing => String): ParseResult[U] = this
@@ -487,7 +489,7 @@ trait Parsers {
     }
 
     /** Changes the error message produced by a parser.
-     * 
+     *
      *  This doesn't change the behavior of a parser on neither
      *  success nor failure, just on error. The semantics are
      *  slightly different than those obtained by doing `| error(msg)`,
@@ -877,16 +879,15 @@ trait Parsers {
    *           if `p` consumed all the input.
    */
   def phrase[T](p: Parser[T]) = new Parser[T] {
-    lastNoSuccess = null
-    def apply(in: Input) = p(in) match {
-      case s @ Success(out, in1) =>
-        if (in1.atEnd)
-          s
-        else if (lastNoSuccess == null || lastNoSuccess.next.pos < in1.pos)
-          Failure("end of input expected", in1)
-        else
-          lastNoSuccess
-      case _ => lastNoSuccess
+    def apply(in: Input) = lastNoSuccess.withValue(None) {
+      p(in) match {
+        case s @ Success(out, in1) =>
+          if (in1.atEnd)
+            s
+          else
+            lastNoSuccess.value filterNot { _.next.pos < in1.pos } getOrElse Failure("end of input expected", in1)
+        case ns => lastNoSuccess.value.getOrElse(ns)
+      }
     }
   }
 

diff --git a/test/files/run/t4929.check b/test/files/run/t4929.check
@@ -0,0 +1 @@
+success
diff --git a/test/files/run/t4929.scala b/test/files/run/t4929.scala
@@ -0,0 +1,42 @@
+import scala.util.parsing.json._
+import java.util.concurrent._
+import collection.JavaConversions._
+
+object Test extends App {
+
+  val LIMIT = 2000
+  val THREAD_COUNT = 20
+  val count = new java.util.concurrent.atomic.AtomicInteger(0)
+
+  val begin = new CountDownLatch(THREAD_COUNT)
+  val finish = new CountDownLatch(THREAD_COUNT)
+
+  val errors = new ConcurrentLinkedQueue[Throwable]
+
+  (1 to THREAD_COUNT) foreach { i =>
+    val thread = new Thread {
+      override def run() {
+        begin.await(1, TimeUnit.SECONDS)
+        try {
+          while (count.getAndIncrement() < LIMIT && errors.isEmpty) {
+            JSON.parseFull("""{"foo": [1,2,3,4]}""")
+          }
+        } catch {
+          case t: Throwable => errors.add(t)
+        }
+
+        finish.await(10, TimeUnit.SECONDS)
+      }
+    }
+
+    thread.setDaemon(true)
+    thread.start()
+
+  }
+
+
+  errors foreach { throw(_) }
+
+  println("success")
+
+}