annotations for j.u.c.locks + related fixes of tests

libraries/stdlib/src/kotlin/concurrent/Locks.kt

@@ -4,6 +4,7 @@ import java.util.concurrent.locks.Lock
 import java.util.concurrent.locks.ReadWriteLock
 import java.util.concurrent.locks.ReentrantReadWriteLock
 import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock
+import java.util.concurrent.CountDownLatch
 
 /**
 Executes given calculation under lock
@@ -24,7 +25,7 @@ Executes given calculation under read lock
 Returns result of the calculation
 */
 public inline fun <T> ReentrantReadWriteLock.read(action: ()->T) : T {
-    val rl = readLock()!!
+    val rl = readLock()
     rl.lock()
     try {
         return action()
@@ -41,12 +42,12 @@ If such write has been initiated by checking some condition, the condition must
 Returns result of the calculation
 */
 public inline fun <T> ReentrantReadWriteLock.write(action: ()->T) : T {
-    val rl = readLock()!!
+    val rl = readLock()
 
     val readCount = if (getWriteHoldCount() == 0) getReadHoldCount() else 0
     readCount times { rl.unlock() }
 
-    val wl = writeLock()!!
+    val wl = writeLock()
     wl.lock()
     try {
         return action()
@@ -56,3 +57,14 @@ public inline fun <T> ReentrantReadWriteLock.write(action: ()->T) : T {
         wl.unlock()
     }
 }
+
+/**
+Execute given calculation and await for CountDownLatch
+Returns result of the calculation
+*/
+fun <T> Int.latch(op:  CountDownLatch.() -> T) : T {
+    val cdl = CountDownLatch(this)
+    val res = cdl.op()
+    cdl.await()
+    return res
+}