How to determine the cause of my SIGTrap Crash?

Question

My team recently launched an application for which there were quite a few SIGTRAP crashes. Previously, I found that they were relatively easy to fix, since it was about finding a bad strength or an implicitly deployed option set to zero in a violating function. This time, although I can not find anything like it. My best guess is that perhaps one of the TimeBlock objects or its properties is zero due to a calendar error.

Our application is the organizer of a meeting in which the user displays their own iOS calendar events in terms of FreeTime, Conflicts, and Meeting TimeBlocks . I have access to calendars of several users who crashed.

Apple SigTrap Definition

Swift code will exit with this type of exception if an unexpected condition occurs at run time, for example:

• optional type with null value
• failed type conversion

Fault function

  /** Updates the conflictHours and meetingHours according to the timeblocks it is used as quick light reference to the button */ func updateTimeHours(timeblocks : [Timeblock]) { for timeblock in timeblocks { switch timeblock { case is MeetingTimeblock: for i in timeblock.startHour...timeblock.endHour { self.meetingHours[i] = true } break case is ConflictTimeblock: for i in timeblock.startHour...timeblock.endHour { self.conflictsHours[i] = true } break default: break } } updateButtonByOffset(offset: self.scrollTimeline.contentOffset.x) } 

Call Failure Function

  /** This function inits the variables and button layout according to the timeblocks */ func handleTimeblocksDependantComponents() { buttonLayout() guard Scheduler.sharedInstance.timelines.count > SharedGlobals.Calendar.TODAY_INDEX else { return } updateTimeHours(timeblocks : (Scheduler.sharedInstance.timelines[SharedGlobals.Calendar.TODAY_INDEX].timeblocks)) } 

Setheaderheight

 /** Adjusts the height of the header depending on whether there are hosted meetings or meeting VIP or not. */ private func setHeaderHeight() { self.tableView.tableHeaderView = self.headerView let hostedMeetings = OverviewInteractor.getHostedMeetings(dayIndex: SharedGlobals.Calendar.SELECTED_DAY) let vips = OverviewInteractor.getVIPS(dayIndex: SharedGlobals.Calendar.SELECTED_DAY) self.tableView.beginUpdates() if let headerView = self.tableView.tableHeaderView { var height = 360.0 if(vips.count == 0) { height -= 80.0 } if(hostedMeetings.count == 0) { height -= 80.0 } headerView.frame.size.height = CGFloat(height) } self.tableView.endUpdates() } 

TimeBlock Definition

 // The Timeblock parent class. It simply holds a start and end time and provides its own duration. Not to be used as such public class Timeblock { public let startTime: Date public let endTime: Date /// Returns the hour the Timeblock starts, in current timezone public var startHour: Int { get { return Calendar.current.component(.hour, from: startTime) } } /// Returns the hour the Timeblocks ends, in current timezone public var endHour: Int { get { return Calendar.current.component(.hour, from: endTime) } } /// Returns the minutes the Timeblocks starts public var startMinutes: Int { get { return Calendar.current.component(.minute, from: startTime) } } /// Returns the minutes the Timeblocks ends public var endMinutes: Int { get { return Calendar.current.component(.minute, from: endTime) } } /** Initialises the instance with a start and end time - Parameters: - startTime: The start time of the timeblock - endTime: The end time of the timeblock */ public init(startTime: Date, endTime: Date) { self.startTime = startTime self.endTime = endTime } /** Provides the Timeblock duration in the form of a DateInterval - warning: Only available on iOS 10.0 and up - returns: A DateInterval of the duration of the Timeblock */ @available(iOS 10.0, *) public func getTimeInterval() -> DateInterval { return DateInterval(start: self.startTime, end: self.endTime) } /** Provides the Timeblock duration in the form of a `Double` (number of seconds) - returns: The number of seconds that this Timeblock goes on for */ public func getDuration() -> Double { return self.endTime.timeIntervalSince(self.startTime) } } 

Crash report

Incident ID: 98D4F477-C57B-4767-B957-E9EA2E0EE3EA CrashReporter Key: 00000000000000000000000000000000000000000000 Hardware Model: undefined Process: xxxxxxx [784] Identifier:
com.xxx.xxx.xx.xxxxxxx Version: 4.0.3 Code type:
arm64

Date / Time: Sun Dec 24 2017 09:55:23 GMT + 0000 (GMT) Start Time: Invalid date OS version: undefined 11.0.3 (15A432) Report version: 105

Exception Type: SIGTRAP Exception Subtype: undefined

Thread 0 name: Thread 0 Crashed: 0 CallIn
0x0000000102c224e4 specialized TimelineHeader.updateTimeHours (timeblocks :) (TimelineHeader.swift: 0) 1 CallIn 0x0000000102c20af0 TimelineHeader.handleTimeblocksDependantComponents () (TimelineHeader.swift: 0) 2 CallIn
0x0000000102c7a28c specialized MeetingTableViewController.tableView (: viewForHeaderInSection :) (TimelineHeader.swift: 78) 3 CallIn
0x0000000102c75d54 @objc MeetingTableViewController.tableView (: viewForHeaderInSection :) (MeetingTableViewController.swift: 0) 4 UIKit
0x000000018d1157d8 - [UITableView _delegateViewForHeaderInSection:] (UIKit) 5 UIKit 0x000000018d11def0 96- [UITableView _sectionHeaderView: withFrame: forSection: floating: reuseViewIfPrivate UitIit (UIT) UIT (UIT) UIT8 (UIKit) UIT8 (UIKit) UIT6 (UIKit) ) 7 UIKit 0x000000018d11dc60 - [UITableView _sectionHeaderView: withFrame : forSection: floating: reuseViewIfPossible: willDisplay:] (UIKit ) 8 UIKit 0x000000018cfc6c04 - [_ UITableViewUpdateSupport (Private ) _setupAnimationsForExistingHeadersAndFooters] (UIKit) 9 UIKit 0x000000018cfc1070 - [_ UITableViewUpdateSupport _setupAnimations] (UIKit) 10 UIKit 0x000000018cfc0944 - [UITableView _updateWithItems: updateSupport:] (UIKit) 11 UIKit 0x000000018cfa8448 - [UITableView endCellAnimationsWithContext:] (UIKit) 12 UIKit 0x000000018cfa46e4ent1e01itUcend01e01t010101c0140101010101010101010101010101010101010101010101010101010101p011 whichent that is used to set up 0x000000018cfa46e02ent01UcIcIt4eUdcTeUtableItem 0x000000018cUcIt4tUpItent () (MeetingTableViewController.swift: 398) 14 CallIn
0x0000000102c7a7c8 specialized closure # 1 in MeetingTableViewController.refreshTable (:) (MeetingTableViewController.swift: 513) 15 CallIn
0x0000000102c7aacc is partially used to close No. 1 in MeetingTableViewController.refreshTable (_ :) (MeetingTableViewController.swift: 0) 16 CallIn
0x0000000102cd17f0 thunk for @callee_owned () → () (LoginPageViewController.swift: 0) 17 libdispatch.dylib
0x000000018327ea54 _dispatch_call_block_and_release (libdispatch.dylib) 18 libdispatch.dylib
0x000000018327ea14 _dispatch_client_callout (libdispatch.dylib) 19 libdispatch.dylib 0x000000018328b698 _dispatch_main_queue_callback_4CF $ VARIANT $ mp ( libdispatch.dylib) 20 CoreFoundation 0x00000001838aa544 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE (CoreFoundation) 21 CoreFoundation 0x00000001838a8120 __CFRunLoopRun (CoreFoundation) 22 CoreFoundation
0x00000001837c7e58 CFRunLoopRunSpecific (CoreFoundation) 23 GraphicsServices 0x0000000185674f84 GSEventRunModal (GraphicsServices) 24 UIKit
0x000000018ce4767c UIApplicationMain (UIKit) 25 CallIn
0x0000000102c02c08 main (AppDelegate.swift: 18) 26 libdyld.dylib
0x00000001832e456c start (libdyld.dylib)

Answer 1

Play

This was because the index got confused with Timeblock.startHour and Timeblock.endHour as Int . Looking at our users calendars, I noticed that all of them had meetings that ended at midnight.

So, for the meeting, which lasted between 5pm until midnight, we got the following.

for i in timeblock.startHour...timeblock.endHour became for i in 0...17

This would give a fairly accurate error, indicating that I could not go backwards as soon as I reproduced the crash, which unfortunately did not appear in the crash report, which was a little misleading.

Fix

We limited the time creating the Timeblock.endHour property, so > 0:00 next day was changed to 23:59 to prevent this. The fix was just capping by attaching the cap to >= 0:00 .

The future refactor is likely to set the final hour for all times that end at an hour before the previous hour, as technically, if your meeting ends at 11:00, you will still have an free hour. I would also like to handle all of this inside a Timeblock object, rather than filtering the argument used to create it.