1 package kotlinx.coroutines
2
3 import kotlinx.coroutines.internal.*
4 import kotlin.coroutines.*
5
6 /**
7 * Helper function for coroutine builder implementations to handle uncaught and unexpected exceptions in coroutines,
8 * that could not be otherwise handled in a normal way through structured concurrency, saving them to a future, and
9 * cannot be rethrown. This is a last resort handler to prevent lost exceptions.
10 *
11 * If there is [CoroutineExceptionHandler] in the context, then it is used. If it throws an exception during handling
12 * or is absent, all instances of [CoroutineExceptionHandler] found via [ServiceLoader] and
13 * [Thread.uncaughtExceptionHandler] are invoked.
14 */
15 @InternalCoroutinesApi
handleCoroutineExceptionnull16 public fun handleCoroutineException(context: CoroutineContext, exception: Throwable) {
17 // Invoke an exception handler from the context if present
18 try {
19 context[CoroutineExceptionHandler]?.let {
20 it.handleException(context, exception)
21 return
22 }
23 } catch (t: Throwable) {
24 handleUncaughtCoroutineException(context, handlerException(exception, t))
25 return
26 }
27 // If a handler is not present in the context or an exception was thrown, fallback to the global handler
28 handleUncaughtCoroutineException(context, exception)
29 }
30
handlerExceptionnull31 internal fun handlerException(originalException: Throwable, thrownException: Throwable): Throwable {
32 if (originalException === thrownException) return originalException
33 return RuntimeException("Exception while trying to handle coroutine exception", thrownException).apply {
34 addSuppressed(originalException)
35 }
36 }
37
38 /**
39 * Creates a [CoroutineExceptionHandler] instance.
40 * @param handler a function which handles exception thrown by a coroutine
41 */
42 @Suppress("FunctionName")
CoroutineExceptionHandlernull43 public inline fun CoroutineExceptionHandler(crossinline handler: (CoroutineContext, Throwable) -> Unit): CoroutineExceptionHandler =
44 object : AbstractCoroutineContextElement(CoroutineExceptionHandler), CoroutineExceptionHandler {
45 override fun handleException(context: CoroutineContext, exception: Throwable) =
46 handler.invoke(context, exception)
47 }
48
49 /**
50 * An optional element in the coroutine context to handle **uncaught** exceptions.
51 *
52 * Normally, uncaught exceptions can only result from _root_ coroutines created using the [launch][CoroutineScope.launch] builder.
53 * All _children_ coroutines (coroutines created in the context of another [Job]) delegate handling of their
54 * exceptions to their parent coroutine, which also delegates to the parent, and so on until the root,
55 * so the `CoroutineExceptionHandler` installed in their context is never used.
56 * Coroutines running with [SupervisorJob] do not propagate exceptions to their parent and are treated like root coroutines.
57 * A coroutine that was created using [async][CoroutineScope.async] always catches all its exceptions and represents them
58 * in the resulting [Deferred] object, so it cannot result in uncaught exceptions.
59 *
60 * ### Handling coroutine exceptions
61 *
62 * `CoroutineExceptionHandler` is a last-resort mechanism for global "catch all" behavior.
63 * You cannot recover from the exception in the `CoroutineExceptionHandler`. The coroutine had already completed
64 * with the corresponding exception when the handler is called. Normally, the handler is used to
65 * log the exception, show some kind of error message, terminate, and/or restart the application.
66 *
67 * If you need to handle exception in a specific part of the code, it is recommended to use `try`/`catch` around
68 * the corresponding code inside your coroutine. This way you can prevent completion of the coroutine
69 * with the exception (exception is now _caught_), retry the operation, and/or take other arbitrary actions:
70 *
71 * ```
72 * scope.launch { // launch child coroutine in a scope
73 * try {
74 * // do something
75 * } catch (e: Throwable) {
76 * // handle exception
77 * }
78 * }
79 * ```
80 *
81 * ### Uncaught exceptions with no handler
82 *
83 * When no handler is installed, exception are handled in the following way:
84 * - If exception is [CancellationException], it is ignored, as these exceptions are used to cancel coroutines.
85 * - Otherwise, if there is a [Job] in the context, then [Job.cancel] is invoked.
86 * - Otherwise, as a last resort, the exception is processed in a platform-specific manner:
87 * - On JVM, all instances of [CoroutineExceptionHandler] found via [ServiceLoader], as well as
88 * the current thread's [Thread.uncaughtExceptionHandler], are invoked.
89 * - On Native, the whole application crashes with the exception.
90 * - On JS, the exception is logged via the Console API.
91 *
92 * [CoroutineExceptionHandler] can be invoked from an arbitrary thread.
93 */
94 public interface CoroutineExceptionHandler : CoroutineContext.Element {
95 /**
96 * Key for [CoroutineExceptionHandler] instance in the coroutine context.
97 */
98 public companion object Key : CoroutineContext.Key<CoroutineExceptionHandler>
99
100 /**
101 * Handles uncaught [exception] in the given [context]. It is invoked
102 * if coroutine has an uncaught exception.
103 */
handleExceptionnull104 public fun handleException(context: CoroutineContext, exception: Throwable)
105 }
106