连续启动 crash 自修复技术实现与原理解析

摘要：如果 app 连续 crash 两次无法启动，用户往往会选择卸载。本文介绍如何该类 crash 的自修复技术。

点此查看原文：http://click.aliyun.com/m/41487/

作者：阿里云-移动云-大前端团队

前言
如果 app 连续 crash 两次无法启动，用户往往会选择卸载。

连续启动 crash 应该是 crash 类型中最严重的一类，该问题常常与数据库操作有关，比如：数据库损坏、服务端返回数据错误，存入数据库，app 读取时产生数组越界、找不到方法。

那么除了热修复，能否“自修复”该问题呢？

在微信读书团队发布的《iOS 启动连续闪退保护方案》一文中，给出了连续启动crash的自修复技术的思路讲解，并在GitHub上给出了技术实现，并开源了 GYBootingProtection。方案思路很好，很轻量级。

实现原理

在微信读书团队给出的文章中已经有比较详细的阐述，在此不做赘述，实现的流程图如下所示：

图片描述

但有个实现上可以优化下，可以降低50%以上误报机率，监听用户手动划掉 APP 这个事件，其中一些特定场景，是可以获取的。另外在这里也给出对其 API 设计的建议。最后给出优化后的实现。

优化：降低50%以上误报机率

用户主动 kill 掉 APP 分为两种情况：

App在前台时用户手动划掉APP的时候
APP在后台时划掉APP
第一种场景更为常见，可以通过监听 UIApplicationWillTerminateNotification 来捕获该动作，捕获后恢复计数。第二种情况，无法监听到。但也足以降低 50% 以上的误报机率。

对原有API设计的几点优化意见

1. 机制状态应当用枚举来做为API透出
该机制当前所处的状态，比如：NeedFix 、isFixing，建议用枚举来做为API透出。比如：

APP 启动正常
正在检测是否会在特定时间内是否会 Crash，注意：检测状态下“连续启动崩溃计数”个数小于或等于上限值
APP 出现连续启动 Crash，需要采取修复措施
APP 出现连续启动 Crash，正在修复中

2. 关键数值应当做为初始化参数供用户设置

当前启动Crash的状态
达到需要执行上报操作的“连续启动崩溃计数”个数。
达到需要执行修复操作的“连续启动崩溃计数”个数。
APP 启动后经过多少秒，可以将“连续启动崩溃计数”清零

3. 修复、上报逻辑应当支持用户异步操作

reportBlock 上报逻辑，
repairtBlock 修复逻辑

比如：

typedef void (^BoolCompletionHandler)(BOOL succeeded, NSError *error);
typedef void (^RepairBlock)(ABSBoolCompletionHandler completionHandler);

用户执行 BoolCompletionHandler 后即可知道是否执行完毕，并且支持异步操作。

异步操作带来的问题，可以通过前面提到的枚举API来实时监测状态，来决定各种其他操作。

什么时候会出现该异常？

连续启动 crash 自修复技术实现与原理解析
下面给出优化后的代码实现：

//
//  CYLBootingProtection.h
//  
//
//  Created by ChenYilong on 18/01/10.
//  Copyright © 2018年 ChenYilong. All rights reserved.
//#import <Foundation/Foundation.h>typedef void (^ABSBoolCompletionHandler)(BOOL succeeded, NSError *error);
typedef void (^ABSRepairBlock)(ABSBoolCompletionHandler completionHandler);
typedef void (^ABSReportBlock)(NSUInteger crashCounts);typedef NS_ENUM(NSInteger, BootingProtectionStatus) {BootingProtectionStatusNormal,  /**<  APP 启动正常 */BootingProtectionStatusNormalChecking,  /**< 正在检测是否会在特定时间内是否会 Crash，注意：检测状态下“连续启动崩溃计数”个数小于或等于上限值 */BootingProtectionStatusNeedFix, /**< APP 出现连续启动 Crash，需要采取修复措施 */BootingProtectionStatusFixing,   /**< APP 出现连续启动 Crash，正在修复中... */
};/**
* 启动连续 crash 保护。
* 启动后 `_crashOnLaunchTimeIntervalThreshold` 秒内 crash，反复超过 `_continuousCrashOnLaunchNeedToReport` 次则上报日志，超过 `_continuousCrashOnLaunchNeedToFix` 则启动修复操作。
*/
@interface CYLBootingProtection : NSObject/**
* 启动连续 crash 保护方法。
* 前置条件：在 App 启动时注册 crash 处理函数，在 crash 时调用[CYLBootingProtection addCrashCountIfNeeded]。
* 启动后一定时间内（`crashOnLaunchTimeIntervalThreshold`秒内）crash，反复超过一定次数（`continuousCrashOnLaunchNeedToReport`次）则上报日志，超过一定次数（`continuousCrashOnLaunchNeedToFix`次）则启动修复程序；在一定时间内（`crashOnLaunchTimeIntervalThreshold`秒） 秒后若没有 crash 将“连续启动崩溃计数”计数置零。`reportBlock` 上报逻辑，`repairtBlock` 修复逻辑，完成后执行 `[self setCrashCount:0]`*/
- (void)launchContinuousCrashProtect;/*!
* 当前启动Crash的状态
*/
@property (nonatomic, assign, readonly) BootingProtectionStatus bootingProtectionStatus;/*!
* 达到需要执行上报操作的“连续启动崩溃计数”个数。
*/
@property (nonatomic, assign, readonly) NSUInteger continuousCrashOnLaunchNeedToReport;/*!
* 达到需要执行修复操作的“连续启动崩溃计数”个数。
*/
@property (nonatomic, assign, readonly) NSUInteger continuousCrashOnLaunchNeedToFix;/*!
* APP 启动后经过多少秒，可以将“连续启动崩溃计数”清零
*/
@property (nonatomic, assign, readonly) NSTimeInterval crashOnLaunchTimeIntervalThreshold;/*!
* 借助 context 可以让多个模块注册事件，并且事件 block 能独立执行，互不干扰。
*/
@property (nonatomic, copy, readonly) NSString *context;/*!
* @details 启动后kCrashOnLaunchTimeIntervalThreshold秒内crash，反复超过continuousCrashOnLaunchNeedToReport次则上报日志，超过continuousCrashOnLaunchNeedToFix则启动修复程序；当所有操作完成后，执行 completion。在 crashOnLaunchTimeIntervalThreshold 秒后若没有 crash 将 kContinuousCrashOnLaunchCounterKey 计数置零。
* @param context 借助 context 可以让多个模块注册事件，并且事件 block 能独立执行，互不干扰。
*/
- (instancetype)initWithContinuousCrashOnLaunchNeedToReport:(NSUInteger)continuousCrashOnLaunchNeedToReportcontinuousCrashOnLaunchNeedToFix:(NSUInteger)continuousCrashOnLaunchNeedToFixcrashOnLaunchTimeIntervalThreshold:(NSTimeInterval)crashOnLaunchTimeIntervalThresholdcontext:(NSString *)context;
/*!
* 当前“连续启动崩溃“的状态
*/
+ (BootingProtectionStatus)bootingProtectionStatusWithContext:(NSString *)context continuousCrashOnLaunchNeedToFix:(NSUInteger)continuousCrashOnLaunchNeedToFix;/*!
* 设置上报逻辑，参数 crashCounts 为启动连续 crash 次数
*/
- (void)setReportBlock:(ABSReportBlock)reportBlock;/*!
* 设置修复逻辑
*/
- (void)setRepairBlock:(ABSRepairBlock)repairtBlock;+ (void)setLogger:(void (^)(NSString *))logger;@end
//
//  CYLBootingProtection.m
//
//
//  Created by ChenYilong on 18/01/10.
//  Copyright © 2018年 ChenYilong. All rights reserved.
//#import "CYLBootingProtection.h"
#import <UIKit/UIKit.h>static dispatch_queue_t _exceptionOperationQueue = 0;
void (^Logger)(NSString *log);@interface CYLBootingProtection ()@property (nonatomic, assign) NSUInteger continuousCrashOnLaunchNeedToReport;
@property (nonatomic, assign) NSUInteger continuousCrashOnLaunchNeedToFix;
@property (nonatomic, assign) NSTimeInterval crashOnLaunchTimeIntervalThreshold;
@property (nonatomic, copy) NSString *context;
@property (nonatomic, copy) ABSReportBlock reportBlock;
@property (nonatomic, copy) ABSRepairBlock repairBlock;/*!
* 设置“连续启动崩溃计数”个数
*/
- (void)setCrashCount:(NSInteger)count;/*!
* 设置“连续启动崩溃计数”个数
*/
+ (void)setCrashCount:(NSUInteger)count context:(NSString *)context;/*!
* “连续启动崩溃计数”个数
*/
- (NSUInteger)crashCount;/*!
* “连续启动崩溃计数”个数
*/
+ (NSUInteger)crashCountWithContext:(NSString *)context;@end@implementation CYLBootingProtection
+ (void)initialize {static dispatch_once_t onceToken;dispatch_once(&onceToken, ^{_exceptionOperationQueue = dispatch_queue_create("com.ChenYilong.CYLBootingProtection.fileCacheQueue", DISPATCH_QUEUE_SERIAL);});
}
- (instancetype)initWithContinuousCrashOnLaunchNeedToReport:(NSUInteger)continuousCrashOnLaunchNeedToReportcontinuousCrashOnLaunchNeedToFix:(NSUInteger)continuousCrashOnLaunchNeedToFixcrashOnLaunchTimeIntervalThreshold:(NSTimeInterval)crashOnLaunchTimeIntervalThresholdcontext:(NSString *)context {if (!(self = [super init])) {return nil;}_continuousCrashOnLaunchNeedToReport = continuousCrashOnLaunchNeedToReport;_continuousCrashOnLaunchNeedToFix = continuousCrashOnLaunchNeedToFix;_crashOnLaunchTimeIntervalThreshold = crashOnLaunchTimeIntervalThreshold;_context = [context copy];[[NSNotificationCenter defaultCenter] addObserver:selfselector:@selector(applicationWillTerminate:)name:UIApplicationWillTerminateNotificationobject:[UIApplication sharedApplication]];return self;
}/*!
* App在前台时用户手动划掉APP的时候，不计入检测。
* 但是APP在后台时划掉APP，无法检测出来。
* 见：https://stackoverflow.com/a/35041565/3395008
*/
- (void)applicationWillTerminate:(NSNotification *)note {BOOL isNormalChecking = [self isNormalChecking];if (isNormalChecking) {[self decreaseCrashCount];}
}- (void)dealloc {[[NSNotificationCenter defaultCenter] removeObserver:self];
}/*
支持同步修复、异步修复，两种修复方式
- 异步修复，不卡顿主UI，但有修复未完成就被再次触发crash、或者用户kill掉的可能。需要用户手动根据修复状态，来选择性地进行操作，应该有回掉。
- 同步修复，最简单直观，在主线程删除或者下载修复包。
*/
- (void)launchContinuousCrashProtect {NSAssert(_repairBlock, @"_repairBlock is nil!");[[self class] Logger:@"CYLBootingProtection: Launch continuous crash report"];[self resetBootingProtectionStatus];NSUInteger launchCrashes = [self crashCount];// 上报if (launchCrashes >= self.continuousCrashOnLaunchNeedToReport) {NSString *logString = [NSString stringWithFormat:@"CYLBootingProtection: App has continuously crashed for %@ times. Now synchronize uploading crash report and begin fixing procedure.", @(launchCrashes)];[[self class] Logger:logString];if (_reportBlock) {dispatch_async(dispatch_get_main_queue(),^{_reportBlock(launchCrashes);});}}// 修复if ([self isUpToBootingProtectionCount]) {[[self class] Logger:@"need to repair"];[self setIsFixing:YES];if (_repairBlock) {ABSBoolCompletionHandler completionHandler = ^(BOOL succeeded, NSError *__nullable error){if (succeeded) {[self resetCrashCount];} else {[[self class] Logger:error.description];}};dispatch_async(dispatch_get_main_queue(),^{_repairBlock(completionHandler);});}} else {[self increaseCrashCount:launchCrashes];// 正常流程，无需修复[[self class] Logger:@"need no repair"];// 记录启动时刻，用于计算启动连续 crash// 重置启动 crash 计数dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(self.crashOnLaunchTimeIntervalThreshold * NSEC_PER_SEC)), dispatch_get_main_queue(), ^(void){// APP活过了阈值时间，重置崩溃计数NSString *logString = [NSString stringWithFormat:@"CYLBootingProtection: long live the app ( more than %@ seconds ), now reset crash counts", @(self.crashOnLaunchTimeIntervalThreshold)];[[self class] Logger:logString];[self resetCrashCount];});}
}//减少计数的时机：用户手动划掉APP
- (void)decreaseCrashCount {NSUInteger oldCrashCount = [self crashCount];[self decreaseCrashCountWithOldCrashCount:oldCrashCount];
}- (void)decreaseCrashCountWithOldCrashCount:(NSUInteger)oldCrashCount {dispatch_sync(_exceptionOperationQueue, ^{if (oldCrashCount > 0) {[self setCrashCount:oldCrashCount-1];}[self resetBootingProtectionStatus];});
}//重制计数的时机：修复完成、或者用户手动划掉APP
- (void)resetCrashCount {[self setCrashCount:0];[self resetBootingProtectionStatus];
}//只在未达到计数上限时才会增加计数
- (void)increaseCrashCount:(NSUInteger)oldCrashCount {dispatch_sync(_exceptionOperationQueue, ^{[self setIsNormalChecking:YES];[self setCrashCount:oldCrashCount+1];});
}- (void)resetBootingProtectionStatus {[self setIsNormalChecking:NO];[self setIsFixing:NO];
}- (BootingProtectionStatus)bootingProtectionStatus {return [[self class] bootingProtectionStatusWithContext:_context continuousCrashOnLaunchNeedToFix:_continuousCrashOnLaunchNeedToFix];
}/*!
*
@attention 注意之所以要检查 `BootingProtectionStatusNormalChecking` 原因如下：`-launchContinuousCrashProtect` 方法与 `-bootingProtectionStatus` 方法，如果 `-launchContinuousCrashProtect` 先执行，那么会造成如下问题：
假设n为上限，但crash（n-1）次，但是用 `-bootingProtectionStatus` 判断出来，当前已经处于n次了。原因如下：crash（n-1）次，正常流程，计数+1，变成n次，
随后在检查 `-bootingProtectionStatus` 时，发现已经处于异常状态了，实际是正常状态。所以需要使用`BootingProtectionStatusNormalChecking` 来进行区分。
*/
+ (BootingProtectionStatus)bootingProtectionStatusWithContext:(NSString *)context continuousCrashOnLaunchNeedToFix:(NSUInteger)continuousCrashOnLaunchNeedToFix {BOOL isNormalChecking = [self isNormalCheckingWithContext:context];if (isNormalChecking) {return BootingProtectionStatusNormalChecking;}BOOL isUpToBootingProtectionCount = [self isUpToBootingProtectionCountWithContext:contextcontinuousCrashOnLaunchNeedToFix:continuousCrashOnLaunchNeedToFix];if (!isUpToBootingProtectionCount) {return BootingProtectionStatusNormal;}BootingProtectionStatus type;BOOL isFixingCrash = [self isFixingCrashWithContext:context];if (isFixingCrash) {type = BootingProtectionStatusFixing;} else {type = BootingProtectionStatusNeedFix;}return type;
}- (NSUInteger)crashCount {return [[self class] crashCountWithContext:_context];
}- (void)setCrashCount:(NSInteger)count {if (count >=0) {[[self class] setCrashCount:count context:_context];}
}- (void)setIsFixing:(BOOL)isFixingCrash {[[self class] setIsFixing:isFixingCrash context:_context];
}/*!
* 是否正在修复
*/
- (BOOL)isFixingCrash {return [[self class] isFixingCrashWithContext:_context];
}- (void)setIsNormalChecking:(BOOL)isNormalChecking {[[self class] setIsNormalChecking:isNormalChecking context:_context];
}/*!
* 是否正在检查
*/
- (BOOL)isNormalChecking {return [[self class] isNormalCheckingWithContext:_context];
}+ (NSUInteger)crashCountWithContext:(NSString *)context {NSString *continuousCrashOnLaunchCounterKey = [self continuousCrashOnLaunchCounterKeyWithContext:context];NSUInteger crashCount = [[NSUserDefaults standardUserDefaults] integerForKey:continuousCrashOnLaunchCounterKey];NSString *logString = [NSString stringWithFormat:@"crashCount:%@", @(crashCount)];[[self class] Logger:logString];return crashCount;
}+ (void)setCrashCount:(NSUInteger)count context:(NSString *)context {NSString *continuousCrashOnLaunchCounterKey = [self continuousCrashOnLaunchCounterKeyWithContext:context];NSString *logString = [NSString stringWithFormat:@"setCrashCount:%@", @(count)];[[self class] Logger:logString];NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];[defaults setInteger:count forKey:continuousCrashOnLaunchCounterKey];[defaults synchronize];
}+ (void)setIsFixing:(BOOL)isFixingCrash context:(NSString *)context {NSString *continuousCrashFixingKey = [[self class] continuousCrashFixingKeyWithContext:context];NSString *logString = [NSString stringWithFormat:@"setisFixingCrash:{%@}", @(isFixingCrash)];[[self class] Logger:logString];NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];[defaults setBool:isFixingCrash forKey:continuousCrashFixingKey];[defaults synchronize];
}+ (BOOL)isFixingCrashWithContext:(NSString *)context {NSString *continuousCrashFixingKey = [[self class] continuousCrashFixingKeyWithContext:context];BOOL isFixingCrash = [[NSUserDefaults standardUserDefaults] boolForKey:continuousCrashFixingKey];NSString *logString = [NSString stringWithFormat:@"isFixingCrash:%@", @(isFixingCrash)];[[self class] Logger:logString];return isFixingCrash;
}+ (void)setIsNormalChecking:(BOOL)isNormalChecking context:(NSString *)context {NSString *continuousCrashNormalCheckingKey = [[self class] continuousCrashNormalCheckingKeyWithContext:context];NSString *logString = [NSString stringWithFormat:@"setIsNormalChecking:{%@}", @(isNormalChecking)];[[self class] Logger:logString];NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];[defaults setBool:isNormalChecking forKey:continuousCrashNormalCheckingKey];[defaults synchronize];
}+ (BOOL)isNormalCheckingWithContext:(NSString *)context {NSString *continuousCrashFixingKey = [[self class] continuousCrashNormalCheckingKeyWithContext:context];BOOL isFixingCrash = [[NSUserDefaults standardUserDefaults] boolForKey:continuousCrashFixingKey];NSString *logString = [NSString stringWithFormat:@"isIsNormalChecking:%@", @(isFixingCrash)];[[self class] Logger:logString];return isFixingCrash;
}- (BOOL)isUpToBootingProtectionCount {return [[self class] isUpToBootingProtectionCountWithContext:_context continuousCrashOnLaunchNeedToFix:_continuousCrashOnLaunchNeedToFix];
}+ (BOOL)isUpToBootingProtectionCountWithContext:(NSString *)context continuousCrashOnLaunchNeedToFix:(NSUInteger)continuousCrashOnLaunchNeedToFix {BOOL isUpToCount = [self crashCountWithContext:context] >= continuousCrashOnLaunchNeedToFix;if (isUpToCount) {return YES;}return NO;
}- (void)setReportBlock:(ABSReportBlock)block {_reportBlock = block;
}- (void)setRepairBlock:(ABSRepairBlock)block {_repairBlock = block;
}/*!
*  “连续启动崩溃计数”个数，对应的Key
*  默认为 "_CONTINUOUS_CRASH_COUNTER_KEY"
*/
+ (NSString *)continuousCrashOnLaunchCounterKeyWithContext:(NSString *)context {BOOL isValid = [[self class] isValidString:context];NSString *validContext = isValid ? context : @"";NSString *continuousCrashOnLaunchCounterKey = [NSString stringWithFormat:@"%@_CONTINUOUS_CRASH_COUNTER_KEY", validContext];return continuousCrashOnLaunchCounterKey;
}/*!
*  是否正在修复记录，对应的Key
*  默认为 "_CONTINUOUS_CRASH_FIXING_KEY"
*/
+ (NSString *)continuousCrashFixingKeyWithContext:(NSString *)context {BOOL isValid = [[self class] isValidString:context];NSString *validContext = isValid ? context : @"";NSString *continuousCrashFixingKey = [NSString stringWithFormat:@"%@_CONTINUOUS_CRASH_FIXING_KEY", validContext];return continuousCrashFixingKey;
}/*!
*  是否正在检查是否在特定时间内会Crash，对应的Key
*  默认为 "_CONTINUOUS_CRASH_CHECKING_KEY"
*/
+ (NSString *)continuousCrashNormalCheckingKeyWithContext:(NSString *)context {BOOL isValid = [[self class] isValidString:context];NSString *validContext = isValid ? context : @"";NSString *continuousCrashFixingKey = [NSString stringWithFormat:@"%@_CONTINUOUS_CRASH_CHECKING_KEY", validContext];return continuousCrashFixingKey;
}#pragma mark -
#pragma mark - log and util Methods+ (void)setLogger:(void (^)(NSString *))logger {Logger = [logger copy];
}+ (void)Logger:(NSString *)log {if (Logger) Logger(log);
}+ (BOOL)isValidString:(id)notValidString {if (!notValidString) {return NO;}if (![notValidString isKindOfClass:[NSString class]]) {return NO;}NSInteger stringLength = 0;@try {stringLength = [notValidString length];} @catch (NSException *exception) {}if (stringLength == 0) {return NO;}return YES;
}@end

下面是相应的验证步骤：

等待15秒会有对应计数清零的操作日志输出：

2018-01-18 16:25:37.162980+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：CYLBootingProtection: Launch continuous crash report
2018-01-18 16:25:37.163140+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setIsNormalChecking:{0}
2018-01-18 16:25:37.165738+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setisFixingCrash:{0}
2018-01-18 16:25:37.166883+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：crashCount:0
2018-01-18 16:25:37.167102+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：crashCount:0
2018-01-18 16:25:37.167253+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setIsNormalChecking:{1}
2018-01-18 16:25:37.167938+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setCrashCount:1
2018-01-18 16:25:37.168806+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：need no repair2018-01-18 16:25:52.225197+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：CYLBootingProtection: long live the app ( more than 15 seconds ), now reset crash counts
2018-01-18 16:25:52.225378+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setCrashCount:0
2018-01-18 16:25:52.226234+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setIsNormalChecking:{0}
2018-01-18 16:25:52.226595+0800 BootingProtection[89773:15553277] 类名与方法名：-[AppDelegate onBeforeBootingProtection]_block_invoke（在第45行），描述：setisFixingCrash:{0}