Mutex.withLock() added EXACTLY_ONCE contract

kotlinx-coroutines-core/common/src/sync/Mutex.kt

@@ -9,6 +9,9 @@ import kotlinx.coroutines.*
 import kotlinx.coroutines.internal.*
 import kotlinx.coroutines.intrinsics.*
 import kotlinx.coroutines.selects.*
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.coroutines.*
 import kotlin.jvm.*
 import kotlin.native.concurrent.*
@@ -106,7 +109,12 @@ public fun Mutex(locked: Boolean = false): Mutex =
  *
  * @return the return value of the action.
  */
+@ExperimentalContracts
 public suspend inline fun <T> Mutex.withLock(owner: Any? = null, action: () -> T): T {
+    contract { 
+        callsInPlace(action, InvocationKind.EXACTLY_ONCE)
+    }
+
     lock(owner)
     try {
         return action()

kotlinx-coroutines-core/common/src/sync/Semaphore.kt

@@ -7,6 +7,9 @@ package kotlinx.coroutines.sync
 import kotlinx.atomicfu.*
 import kotlinx.coroutines.*
 import kotlinx.coroutines.internal.*
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.InvocationKind
+import kotlin.contracts.contract
 import kotlin.coroutines.*
 import kotlin.math.*
 import kotlin.native.concurrent.SharedImmutable
@@ -74,7 +77,12 @@ public fun Semaphore(permits: Int, acquiredPermits: Int = 0): Semaphore = Semaph
  *
  * @return the return value of the [action].
  */
+@ExperimentalContracts
 public suspend inline fun <T> Semaphore.withPermit(action: () -> T): T {
+    contract {
+        callsInPlace(action, InvocationKind.EXACTLY_ONCE)
+    }
+
     acquire()
     try {
         return action()

kotlinx-coroutines-core/common/test/sync/MutexTest.kt

@@ -5,8 +5,10 @@
 package kotlinx.coroutines.sync
 
 import kotlinx.coroutines.*
+import kotlin.contracts.ExperimentalContracts
 import kotlin.test.*
 
+@ExperimentalContracts
 class MutexTest : TestBase() {
     @Test
     fun testSimple() = runTest {

kotlinx-coroutines-core/common/test/sync/SemaphoreTest.kt

@@ -1,6 +1,7 @@
 package kotlinx.coroutines.sync
 
 import kotlinx.coroutines.*
+import kotlin.contracts.ExperimentalContracts
 import kotlin.test.Test
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
@@ -59,6 +60,7 @@ class SemaphoreTest : TestBase() {
         assertEquals(0, semaphore.availablePermits)
     }
 
+    @ExperimentalContracts
     @Test
     fun withSemaphoreTest() = runTest {
         val semaphore = Semaphore(1)

kotlinx-coroutines-core/jvm/test/guide/example-sync-06.kt

@@ -7,6 +7,7 @@ package kotlinx.coroutines.guide.exampleSync06
 
 import kotlinx.coroutines.*
 import kotlinx.coroutines.sync.*
+import kotlin.contracts.ExperimentalContracts
 import kotlin.system.*
 
 suspend fun massiveRun(action: suspend () -> Unit) {
@@ -27,6 +28,7 @@ suspend fun massiveRun(action: suspend () -> Unit) {
 val mutex = Mutex()
 var counter = 0
 
+@ExperimentalContracts
 fun main() = runBlocking {
     withContext(Dispatchers.Default) {
         massiveRun {