{"id":26429,"date":"2019-08-29T15:23:36","date_gmt":"2019-08-29T19:23:36","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=26429"},"modified":"2019-08-29T15:23:36","modified_gmt":"2019-08-29T19:23:36","slug":"the-curious-case-of-the-core-data-crash","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2019\/08\/29\/the-curious-case-of-the-core-data-crash\/","title":{"rendered":"The Curious Case of the Core Data Crash"},"content":{"rendered":"

Sean Heber<\/a>:<\/p>\n

\n

iOS routinely terminates apps for all sorts of reasons, including using too much memory or taking too long to do background processing. I don’t know why this information isn’t included in Xcode’s Organizer, but it’s a critical piece of a debugging puzzle.<\/p>\n

[…]<\/p>\n

But one result let to Tech Note 2151<\/a>, with the code listed at the end under Other Exception Types:<\/p>\n

The exception code 0xdead10cc indicates that an application has been terminated by the OS because it held on to a file lock or sqlite database lock during suspension.<\/p>\n<\/blockquote>

[…]<\/p>\n

I discovered that Twitterrific was sometimes closed while it was doing a network download and iOS left it running in the background long enough for the network request to finish. But not long enough for the database update to finish.<\/p>\n<\/blockquote>\n\n

Sean Heber<\/a>:<\/p>\n

Converting to NSURLSession<\/code> wasn’t very hard and we did it a long time ago. However something had been bothering me and I could never quite pin it down. Specifically, it really felt like network tasks that started while foregrounded and ended while backgrounded were less reliable.<\/p>

[…]<\/p>

I eventually determined that sometimes a request would fail to start and the error code returned by the NSURLSessionDataTask<\/code> would be something odd like NSURLErrorNetworkConnectionLost<\/code> or the ever-helpful NSURLErrorUnknown<\/code>.<\/p>

[…]<\/p>

I scoured the NSURLSession<\/code>s docs looking for a clue and came across something I had missed all the times before - a property called shouldUseExtendedBackgroundIdleMode<\/code> “In addition to requesting that the connection be kept open … when the app moves to the background.”<\/p>

Waitaminute! What is this? Does this mean there’s now an assumption that the connection will NOT be kept open when moving into the background?! Holy buckets on a wagon.<\/p>

It appears that they REALLY want you to use the special background support in NSURLSession<\/code>. In fact they seem to say to go ahead and use it all the time - don’t try to make it conditional.<\/p>

[…]<\/p>

And just like that, the flakiness seemed to be gone. For years I made the assumption that an open NSURLSession<\/code> connection would be allowed to finish as long as you had a background task active like NSURLConnection<\/code> did - but NOPE it doesn’t do that by default!<\/p><\/blockquote>","protected":false},"excerpt":{"rendered":"

Sean Heber: iOS routinely terminates apps for all sorts of reasons, including using too much memory or taking too long to do background processing. I don’t know why this information isn’t included in Xcode’s Organizer, but it’s a critical piece of a debugging puzzle. […] But one result let to Tech Note 2151, with the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"apple_news_api_created_at":"2019-08-29T19:23:39Z","apple_news_api_id":"c045cee8-8939-4b81-a0fa-702433916370","apple_news_api_modified_at":"2019-08-29T19:23:40Z","apple_news_api_revision":"AAAAAAAAAAD\/\/\/\/\/\/\/\/\/\/w==","apple_news_api_share_url":"https:\/\/apple.news\/AwEXO6Ik5S4Gg-nAkM5FjcA","apple_news_coverimage":0,"apple_news_coverimage_caption":"","apple_news_is_hidden":false,"apple_news_is_paid":false,"apple_news_is_preview":false,"apple_news_is_sponsored":false,"apple_news_maturity_rating":"","apple_news_metadata":"\"\"","apple_news_pullquote":"","apple_news_pullquote_position":"","apple_news_slug":"","apple_news_sections":"\"\"","apple_news_suppress_video_url":false,"apple_news_use_image_component":false,"footnotes":""},"categories":[4],"tags":[131,109,31,1610,772,476,71,425,233],"class_list":["post-26429","post","type-post","status-publish","format-standard","hentry","category-programming-category","tag-bug","tag-coredata","tag-ios","tag-ios-12","tag-ios-multitasking","tag-networking","tag-programming","tag-sqlite","tag-twitterrific"],"apple_news_notices":[],"_links":{"self":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/26429","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/comments?post=26429"}],"version-history":[{"count":1,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/26429\/revisions"}],"predecessor-version":[{"id":26430,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/posts\/26429\/revisions\/26430"}],"wp:attachment":[{"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/media?parent=26429"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/categories?post=26429"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mjtsai.com\/blog\/wp-json\/wp\/v2\/tags?post=26429"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}