From a15d20a59838fa1b9a7f63e10f31f475e633f62a Mon Sep 17 00:00:00 2001
From: Vsevolod Tolstopyatov <qwwdfsad@gmail.com>
Date: Fri, 13 Nov 2020 18:50:12 +0300
Subject: [PATCH] Conditionally create an instance of CancellationException in
 Channel.cancel()

Avoid creating costly exception when the channel is cancelled to save a few cycles when it's not necessary. Cancellation is heavy-enough when the channel is open, so the single check won't worsen it.
---
 kotlinx-coroutines-core/common/src/channels/AbstractChannel.kt  | 1 +
 kotlinx-coroutines-core/common/src/channels/ChannelCoroutine.kt | 1 +
 kotlinx-coroutines-core/common/src/flow/internal/Combine.kt     | 2 +-
 3 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/kotlinx-coroutines-core/common/src/channels/AbstractChannel.kt b/kotlinx-coroutines-core/common/src/channels/AbstractChannel.kt
index 8edd2b310c..87bd43714d 100644
--- a/kotlinx-coroutines-core/common/src/channels/AbstractChannel.kt
+++ b/kotlinx-coroutines-core/common/src/channels/AbstractChannel.kt
@@ -635,6 +635,7 @@ internal abstract class AbstractChannel<E>(
         cancelInternal(cause)
 
     final override fun cancel(cause: CancellationException?) {
+        if (isClosedForReceive) return // Do not create an exception if channel is already cancelled
         cancelInternal(cause ?: CancellationException("$classSimpleName was cancelled"))
     }
 
diff --git a/kotlinx-coroutines-core/common/src/channels/ChannelCoroutine.kt b/kotlinx-coroutines-core/common/src/channels/ChannelCoroutine.kt
index a75d466199..9ceb77ddc2 100644
--- a/kotlinx-coroutines-core/common/src/channels/ChannelCoroutine.kt
+++ b/kotlinx-coroutines-core/common/src/channels/ChannelCoroutine.kt
@@ -26,6 +26,7 @@ internal open class ChannelCoroutine<E>(
     }
 
     final override fun cancel(cause: CancellationException?) {
+        if (isClosedForReceive) return // Do not create an exception if channel is already cancelled
         cancelInternal(cause ?: defaultCancellationException())
     }
 
diff --git a/kotlinx-coroutines-core/common/src/flow/internal/Combine.kt b/kotlinx-coroutines-core/common/src/flow/internal/Combine.kt
index bbdebd08b9..d276e5100a 100644
--- a/kotlinx-coroutines-core/common/src/flow/internal/Combine.kt
+++ b/kotlinx-coroutines-core/common/src/flow/internal/Combine.kt
@@ -137,7 +137,7 @@ internal fun <T1, T2, R> zipImpl(flow: Flow<T1>, flow2: Flow<T2>, transform: sus
             } catch (e: AbortFlowException) {
                 e.checkOwnership(owner = this@unsafeFlow)
             } finally {
-                if (!second.isClosedForReceive) second.cancel()
+                second.cancel()
             }
         }
     }