From 853325139f380e992c39e44f5c547929393a7b86 Mon Sep 17 00:00:00 2001
From: DreamPiggy <lizhuoli1126@126.com>
Date: Fri, 27 Dec 2019 14:39:33 +0800
Subject: [PATCH] Fix the thread safe issue with Downloader and
 DownloaderOperation during cancel #2903

---
 SDWebImage/SDWebImageDownloader.m | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/SDWebImage/SDWebImageDownloader.m b/SDWebImage/SDWebImageDownloader.m
index 30a2132a..46c81ed2 100644
--- a/SDWebImage/SDWebImageDownloader.m
+++ b/SDWebImage/SDWebImageDownloader.m
@@ -354,7 +354,12 @@
     NSOperation<SDWebImageDownloaderOperationInterface> *returnOperation = nil;
     for (NSOperation<SDWebImageDownloaderOperationInterface> *operation in self.downloadQueue.operations) {
         if ([operation respondsToSelector:@selector(dataTask)]) {
-            if (operation.dataTask.taskIdentifier == task.taskIdentifier) {
+            // So we lock the operation here, and in `SDWebImageDownloaderOperation`, we use `@synchonzied (self)`, to ensure the thread safe between these two classes.
+            NSURLSessionTask *operationTask;
+            @synchronized (operation) {
+                operationTask = operation.dataTask;
+            }
+            if (operationTask.taskIdentifier == task.taskIdentifier) {
                 returnOperation = operation;
                 break;
             }