Hide reentrant lock from jvm SynchronousMutex.

Add comment to explain interruptibility for tryLock(timeout) on jvm.

Author: bbrockbernd

atomicfu/src/commonMain/kotlin/kotlinx/atomicfu/locks/SynchronousMutex.kt

@@ -35,6 +35,8 @@ expect class SynchronousMutex() {
      * It is recommended to use [withLock] for safety reasons, so that the acquired lock is always
      * released at the end of your critical section, and [unlock] is never invoked before a successful
      * lock acquisition.     
+     * 
+     * (JVM only) this call can potentially skip line.
      */
     fun tryLock(): Boolean
 
@@ -44,6 +46,8 @@ expect class SynchronousMutex() {
      * 
      * Note: when [tryLock] succeeds the lock needs to be released by [unlock].
      * When [tryLock] does not succeed the lock does not have to be released.
+     * 
+     * (JVM only) throws Interrupted exception when thread is interrupted while waiting for lock.
      */
     fun tryLock(timeout: Duration): Boolean
 

atomicfu/src/jvmMain/kotlin/kotlinx/atomicfu/locks/SynchronousMutex.kt

@@ -6,18 +6,12 @@ import kotlin.time.Duration
 /**
  * This mutex uses a [ReentrantLock].
  * 
- * [getReentrantLock] obtains the actual [ReentrantLock].
  * Construct with `Mutex(reentrantLock)` to create a [SynchronousMutex] that uses an existing instance of [ReentrantLock].
  */
-actual class SynchronousMutex(private val reentrantLock: java.util.concurrent.locks.ReentrantLock) {
-    actual constructor(): this(ReentrantLock())
+actual class SynchronousMutex {
+    private val reentrantLock = ReentrantLock()
     actual fun tryLock(timeout: Duration): Boolean = reentrantLock.tryLock(timeout.inWholeNanoseconds, TimeUnit.NANOSECONDS)
     actual fun tryLock(): Boolean = reentrantLock.tryLock()
     actual fun lock() = reentrantLock.lock()
     actual fun unlock() = reentrantLock.unlock()
-
-    /**
-     * @return the underlying [ReentrantLock]
-     */
-    fun getReentrantLock(): ReentrantLock = reentrantLock
 }