System property to control BlockingChecker extension point for runBlocking

Author: elizarov

binary-compatibility-validator/reference-public-api/kotlinx-coroutines-core.txt

@@ -25,6 +25,8 @@ public abstract interface class kotlinx/coroutines/experimental/BlockingChecker
 }
 
 public final class kotlinx/coroutines/experimental/BuildersKt {
+	public static final field BLOCKING_CHECKER_PROPERTY_NAME Ljava/lang/String;
+	public static final field BLOCKING_CHECKER_VALUE_DISABLE Ljava/lang/String;
 	public static final synthetic fun launch (Lkotlin/coroutines/experimental/CoroutineContext;Lkotlinx/coroutines/experimental/CoroutineStart;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/experimental/Job;
 	public static final fun launch (Lkotlin/coroutines/experimental/CoroutineContext;Lkotlinx/coroutines/experimental/CoroutineStart;Lkotlinx/coroutines/experimental/Job;Lkotlin/jvm/functions/Function1;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/experimental/Job;
 	public static final synthetic fun launch (Lkotlin/coroutines/experimental/CoroutineContext;Lkotlinx/coroutines/experimental/CoroutineStart;Lkotlinx/coroutines/experimental/Job;Lkotlin/jvm/functions/Function2;)Lkotlinx/coroutines/experimental/Job;

core/kotlinx-coroutines-core/src/Builders.kt

@@ -7,6 +7,7 @@
 
 package kotlinx.coroutines.experimental
 
+import internal.*
 import java.util.*
 import java.util.concurrent.locks.*
 import kotlin.coroutines.experimental.*
@@ -31,7 +32,8 @@ import kotlin.coroutines.experimental.*
  * See [newCoroutineContext] for a description of debugging facilities that are available for newly created coroutine.
  *
  * @throws IllegalStateException if blocking is not allowed in current thread.
- *         Blocking is checked by [BlockingChecker] registered in [ServiceLoader]
+ *         Blocking is checked by [BlockingChecker] that is registered via [ServiceLoader],
+ *         unless [BLOCKING_CHECKER_PROPERTY_NAME] system property is set to [BLOCKING_CHECKER_VALUE_DISABLE].
  * @param context context of the coroutine. The default value is an implementation of [EventLoop].
  * @param block the coroutine code.
  */
@@ -50,6 +52,18 @@ public fun <T> runBlocking(context: CoroutineContext = EmptyCoroutineContext, bl
     return coroutine.joinBlocking()
 }
 
+/**
+ * Name of the property to control whether [runBlocking] builder
+ * is restricted via [BlockingChecker] extension points.
+ */
+public const val BLOCKING_CHECKER_PROPERTY_NAME = "kotlinx.coroutines.blocking.checker"
+
+/**
+ * Value of the [BLOCKING_CHECKER_PROPERTY_NAME] to disable installed
+ * [BlockingChecker] and thus allow [runBlocking] in any thread.
+ */
+public const val BLOCKING_CHECKER_VALUE_DISABLE = "disable"
+
 /**
  * Extension point which determines whether invoking [runBlocking] in the current thread is allowed.
  * [runBlocking] discovers all checkers via [ServiceLoader] and invokes [checkRunBlocking] on
@@ -63,6 +77,9 @@ public fun <T> runBlocking(context: CoroutineContext = EmptyCoroutineContext, bl
  *        check(!UiFramework.isInUiThread()) { "runBlocking is not allowed in UI thread" }
  * }
  * ```
+ *
+ * Installed checkers are ignored if "`kotlinx.coroutines.blocking.checker`" ([BLOCKING_CHECKER_PROPERTY_NAME])
+ * system property is set to the value "`disable`" ([BLOCKING_CHECKER_VALUE_DISABLE]).
  */
 public interface BlockingChecker {
     /**
@@ -71,11 +88,24 @@ public interface BlockingChecker {
     fun checkRunBlocking()
 }
 
+private class BlockingCheckerList(private val checkers: Array<BlockingChecker>) : BlockingChecker {
+    override fun checkRunBlocking() = checkers.forEach { it.checkRunBlocking() }
+}
+
 // Nullable to enable DCE when no filters are present in classpath
 private val blockingChecker: BlockingChecker? = run {
-    val filters = ServiceLoader.load(BlockingChecker::class.java).toList().toTypedArray()
-    if (filters.isEmpty()) null else object : BlockingChecker {
-        override fun checkRunBlocking() = filters.forEach { it.checkRunBlocking() }
+    val value = systemProp(BLOCKING_CHECKER_PROPERTY_NAME)
+    when (value) {
+        BLOCKING_CHECKER_VALUE_DISABLE -> null
+        null -> {
+            val checkers = ServiceLoader.load(BlockingChecker::class.java).toList()
+            when (checkers.size) {
+                0 -> null
+                1 -> checkers[0]
+                else -> BlockingCheckerList(checkers.toTypedArray())
+            }
+        }
+        else -> error("System property '$BLOCKING_CHECKER_PROPERTY_NAME' has unrecognized value '$value'")
     }
 }