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【原】Android热更新开源项目Tinker源码解析系列之一：Dex热更新

Tinker是微信的第一个开源项目，主要用于安卓应用bug的热修复和功能的迭代。

Tinker github地址：https://github.com/Tencent/tinker

首先向微信致敬，感谢毫无保留的开源出了这么一款优秀的热更新项目。

因Tinker支持Dex，资源文件及so文件的热更新，本系列将从以下三个方面对Tinker进行源码解析：

Tinker中Dex的热更新也主要分为三个部分，本文也将从这三个方面进行分析：

生成补丁流程
补丁包下发成功后合成全量Dex流程
生成全量Dex后的加载流程

转载请标明本文来源：http://www.cnblogs.com/yyangblog/p/6249715.html
更多内容欢迎star作者的github：https://github.com/LaurenceYang/article
如果发现本文有什么问题和任何建议，也随时欢迎交流~

一、生成补丁流程

当在命令行里面调用tinkerPatchRelease任务时会调用com.tencent.tinker.build.patch.Runner.tinkerPatch()进行生成补丁生成过程。

 1 //gen patch
 2 ApkDecoder decoder = new ApkDecoder(config);
 3 decoder.onAllPatchesStart();
 4 decoder.patch(config.mOldApkFile, config.mNewApkFile);
 5 decoder.onAllPatchesEnd();
 6 
 7 //gen meta file and version file
 8 PatchInfo info = new PatchInfo(config);
 9 info.gen();
10 
11 //build patch
12 PatchBuilder builder = new PatchBuilder(config);
13 builder.buildPatch();

ApkDecoder.patch(File oldFile, File newFile)函数中，

会先对manifest文件进行检测，看其是否有更改，如果发现manifest的组件有新增，则抛出异常，因为目前Tinker暂不支持四大组件的新增。

检测通过后解压apk文件，遍历新旧apk，交给ApkFilesVisitor进行处理。

1 //check manifest change first
2 manifestDecoder.patch(oldFile, newFile);
3 
4 unzipApkFiles(oldFile, newFile);
5 
6 Files.walkFileTree(mNewApkDir.toPath(), new ApkFilesVisitor(config, mNewApkDir.toPath(), mOldApkDir.toPath(), dexPatchDecoder, soPatchDecoder, resPatchDecoder));

ApkFilesVisitor的visitFile函数中，对于dex类型的文件，调用dexDecoder进行patch操作；

对于so类型的文件，使用soDecoder进行patch操作；

对于Res类型文件，使用resDecoder进行操作。

本文中主要是针对dexDecoder进行分析。

 1 public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {
 2 
 3     Path relativePath = newApkPath.relativize(file);
 4 
 5     Path oldPath = oldApkPath.resolve(relativePath);
 6 
 7     File oldFile = null;
 8     //is a new file?!
 9     if (oldPath.toFile().exists()) {
10         oldFile = oldPath.toFile();
11     }
12     String patternKey = relativePath.toString().replace("\", "/");
13 
14     if (Utils.checkFileInPattern(config.mDexFilePattern, patternKey)) {
15         //also treat duplicate file as unchanged
16         if (Utils.checkFileInPattern(config.mResFilePattern, patternKey) && oldFile != null) {
17             resDuplicateFiles.add(oldFile);
18         }
19 
20         try {
21             dexDecoder.patch(oldFile, file.toFile());
22         } catch (Exception e) {
23 //                    e.printStackTrace();
24             throw new RuntimeException(e);
25         }
26         return FileVisitResult.CONTINUE;
27     }
28     if (Utils.checkFileInPattern(config.mSoFilePattern, patternKey)) {
29         //also treat duplicate file as unchanged
30         if (Utils.checkFileInPattern(config.mResFilePattern, patternKey) && oldFile != null) {
31             resDuplicateFiles.add(oldFile);
32         }
33         try {
34             soDecoder.patch(oldFile, file.toFile());
35         } catch (Exception e) {
36 //                    e.printStackTrace();
37             throw new RuntimeException(e);
38         }
39         return FileVisitResult.CONTINUE;
40     }
41     if (Utils.checkFileInPattern(config.mResFilePattern, patternKey)) {
42         try {
43             resDecoder.patch(oldFile, file.toFile());
44         } catch (Exception e) {
45 //                    e.printStackTrace();
46             throw new RuntimeException(e);
47         }
48         return FileVisitResult.CONTINUE;
49     }
50     return FileVisitResult.CONTINUE;

DexDiffDecoder.patch(final File oldFile, final File newFile)
首先检测输入的dex文件中是否有不允许修改的类被修改了，如loader相关的类是不允许被修改的，这种情况下会抛出异常；

如果dex是新增的，直接将该dex拷贝到结果文件；

如果dex是修改的，收集增加和删除的class。oldAndNewDexFilePairList将新旧dex对应关系保存起来，用于后面的分析。

 1 excludedClassModifiedChecker.checkIfExcludedClassWasModifiedInNewDex(oldFile, newFile);
 2 ...
 3 //new add file
 4 if (oldFile == null || !oldFile.exists() || oldFile.length() == 0) {
 5     hasDexChanged = true;
 6     if (!config.mUsePreGeneratedPatchDex) {
 7         copyNewDexAndLogToDexMeta(newFile, newMd5, dexDiffOut);
 8         return true;
 9     }
10 }
11 ...
12 // collect current old dex file and corresponding new dex file for further processing.
13 oldAndNewDexFilePairList.add(new AbstractMap.SimpleEntry<>(oldFile, newFile));

UniqueDexDiffDecoder.patch中将新的dex文件加入到addedDexFiles。

 1 public boolean patch(File oldFile, File newFile) throws IOException, TinkerPatchException {
 2     boolean added = super.patch(oldFile, newFile);
 3     if (added) {
 4         String name = newFile.getName();
 5         if (addedDexFiles.contains(name)) {
 6             throw new TinkerPatchException("illegal dex name, dex name should be unique, dex:" + name);
 7         } else {
 8             addedDexFiles.add(name);
 9         }
10     }
11     return added;
12 }

在patch完成后，会调用generatePatchInfoFile生成补丁文件。
DexFiffDecoder.generatePatchInfoFile中首先遍历oldAndNewDexFilePairList，取出新旧文件对。

判断新旧文件的MD5是否相等，不相等，说明有变化，会根据新旧文件创建DexPatchGenerator，

DexPatchGenerator构造函数中包含了15个Dex区域的比较算法：

StringDataSectionDiffAlgorithm
TypeIdSectionDiffAlgorithm
ProtoIdSectionDiffAlgorithm
FieldIdSectionDiffAlgorithm
MethodIdSectionDiffAlgorithm
ClassDefSectionDiffAlgorithm
TypeListSectionDiffAlgorithm
AnnotationSetRefListSectionDiffAlgorithm
AnnotationSetSectionDiffAlgorithm
ClassDataSectionDiffAlgorithm
CodeSectionDiffAlgorithm
DebugInfoItemSectionDiffAlgorithm
AnnotationSectionDiffAlgorithm
StaticValueSectionDiffAlgorithm
AnnotationsDirectorySectionDiffAlgorithm

DexDiffDecoder.executeAndSaveTo(OutputStream out) 这个函数里面会根据上面的15个算法对dex的各个区域进行比较，最后生成dex文件的差异，

这是整个dex diff算法的核心。以StringDataSectionDiffAlgorithm为例，算法流程如下：

--------------------------------------------

获取oldDex中StringData区域的Item，并进行排序
获取newDex中StringData区域的Item，并进行排序
然后对ITEM依次比较
<0
　说明从老的dex中删除了该String，patchOperationList中添加Del操作
>0
　说明添加了该String，patchOperationList添加add操作
=0
　说明都有该String，记录oldIndexToNewIndexMap，oldOffsetToNewOffsetMap
old item已到结尾
　剩下的item说明都是新增项，patchOperationList添加add操作
new item已到结尾
　剩下的item说明都是删除项，patchOperationList添加del操作
最后对对patchOperationList进行优化（
{OP_DEL idx} followed by {OP_ADD the_same_idx newItem} will be replaced by {OP_REPLACE idx newItem}）

--------------------------------------------

Dexdiff得到的最终生成产物就是针对原dex的一个操作序列。
关于DexDiff算法，更加详细的介绍可以参考https://www.zybuluo.com/dodola/note/554061，算法名曰二路归并。

对每个区域比较后会将比较的结果写入文件中，文件格式写在DexDataBuffer中

 1  private void writeResultToStream(OutputStream os) throws IOException {
 2     DexDataBuffer buffer = new DexDataBuffer();
 3     buffer.write(DexPatchFile.MAGIC);
 4     buffer.writeShort(DexPatchFile.CURRENT_VERSION);
 5     buffer.writeInt(this.patchedDexSize);
 6     // we will return here to write firstChunkOffset later.
 7     int posOfFirstChunkOffsetField = buffer.position();
 8     buffer.writeInt(0);
 9     buffer.writeInt(this.patchedStringIdsOffset);
10     buffer.writeInt(this.patchedTypeIdsOffset);
11     buffer.writeInt(this.patchedProtoIdsOffset);
12     buffer.writeInt(this.patchedFieldIdsOffset);
13     buffer.writeInt(this.patchedMethodIdsOffset);
14     buffer.writeInt(this.patchedClassDefsOffset);
15     buffer.writeInt(this.patchedMapListOffset);
16     buffer.writeInt(this.patchedTypeListsOffset);
17     buffer.writeInt(this.patchedAnnotationSetRefListItemsOffset);
18     buffer.writeInt(this.patchedAnnotationSetItemsOffset);
19     buffer.writeInt(this.patchedClassDataItemsOffset);
20     buffer.writeInt(this.patchedCodeItemsOffset);
21     buffer.writeInt(this.patchedStringDataItemsOffset);
22     buffer.writeInt(this.patchedDebugInfoItemsOffset);
23     buffer.writeInt(this.patchedAnnotationItemsOffset);
24     buffer.writeInt(this.patchedEncodedArrayItemsOffset);
25     buffer.writeInt(this.patchedAnnotationsDirectoryItemsOffset);
26     buffer.write(this.oldDex.computeSignature(false));
27     int firstChunkOffset = buffer.position();
28     buffer.position(posOfFirstChunkOffsetField);
29     buffer.writeInt(firstChunkOffset);
30     buffer.position(firstChunkOffset);
31 
32     writePatchOperations(buffer, this.stringDataSectionDiffAlg.getPatchOperationList());
33     writePatchOperations(buffer, this.typeIdSectionDiffAlg.getPatchOperationList());
34     writePatchOperations(buffer, this.typeListSectionDiffAlg.getPatchOperationList());
35     writePatchOperations(buffer, this.protoIdSectionDiffAlg.getPatchOperationList());
36     writePatchOperations(buffer, this.fieldIdSectionDiffAlg.getPatchOperationList());
37     writePatchOperations(buffer, this.methodIdSectionDiffAlg.getPatchOperationList());
38     writePatchOperations(buffer, this.annotationSectionDiffAlg.getPatchOperationList());
39     writePatchOperations(buffer, this.annotationSetSectionDiffAlg.getPatchOperationList());
40     writePatchOperations(buffer, this.annotationSetRefListSectionDiffAlg.getPatchOperationList());
41     writePatchOperations(buffer, this.annotationsDirectorySectionDiffAlg.getPatchOperationList());
42     writePatchOperations(buffer, this.debugInfoSectionDiffAlg.getPatchOperationList());
43     writePatchOperations(buffer, this.codeSectionDiffAlg.getPatchOperationList());
44     writePatchOperations(buffer, this.classDataSectionDiffAlg.getPatchOperationList());
45     writePatchOperations(buffer, this.encodedArraySectionDiffAlg.getPatchOperationList());
46     writePatchOperations(buffer, this.classDefSectionDiffAlg.getPatchOperationList());
47 
48     byte[] bufferData = buffer.array();
49     os.write(bufferData);
50     os.flush();
51 }

生成的文件以dex结尾，但需要注意的是，它不是真正的dex文件，其格式可参考DexDataBuffer类。

二、补丁包下发成功后合成全量Dex流程

当app收到服务器下发的补丁后，会触发DefaultPatchListener.onPatchReceived事件，

调用TinkerPatchService.runPatchService启动patch进程进行补丁patch工作。

UpgradePatch.tryPatch()中会首先检查补丁的合法性，签名，以及是否安装过补丁，检查通过后会尝试dex，so以及res文件的patch。

本文中主要分析DexDiffPatchInternal.tryRecoverDexFiles，讨论dex的patch过程。

1 DexDiffPatchInternal.tryRecoverDexFiles
2 BsDiffPatchInternal.tryRecoverLibraryFiles
3 ResDiffPatchInternal.tryRecoverResourceFiles
4 rewritePatchInfoFileWithLock

tryRecoverDexFiles调用DexDiffPatchInternal.patchDexFile，

最终通过DexPatchApplier.executeAndSaveTo进行执行及生产全量dex。

 1 private static void patchDexFile(
 2         ZipFile baseApk, ZipFile patchPkg, ZipEntry oldDexEntry, ZipEntry patchFileEntry,
 3         ShareDexDiffPatchInfo patchInfo,  File patchedDexFile) throws IOException {
 4     InputStream oldDexStream = null;
 5     InputStream patchFileStream = null;
 6     try {
 7         oldDexStream = baseApk.getInputStream(oldDexEntry);
 8         patchFileStream = (patchFileEntry != null ? patchPkg.getInputStream(patchFileEntry) : null);
 9 
10         final boolean isRawDexFile = SharePatchFileUtil.isRawDexFile(patchInfo.rawName);
11         if (!isRawDexFile || patchInfo.isJarMode) {
12             ZipOutputStream zos = null;
13             try {
14                 zos = new ZipOutputStream(new BufferedOutputStream(new FileOutputStream(patchedDexFile)));
15                 zos.putNextEntry(new ZipEntry(ShareConstants.DEX_IN_JAR));
16                 // Old dex is not a raw dex file.
17                 if (!isRawDexFile) {
18                     ZipInputStream zis = null;
19                     try {
20                         zis = new ZipInputStream(oldDexStream);
21                         ZipEntry entry;
22                         while ((entry = zis.getNextEntry()) != null) {
23                             if (ShareConstants.DEX_IN_JAR.equals(entry.getName())) break;
24                         }
25                         if (entry == null) {
26                             throw new TinkerRuntimeException("can't recognize zip dex format file:" + patchedDexFile.getAbsolutePath());
27                         }
28                         new DexPatchApplier(zis, (int) entry.getSize(), patchFileStream).executeAndSaveTo(zos);
29                     } finally {
30                         SharePatchFileUtil.closeQuietly(zis);
31                     }
32                 } else {
33                     new DexPatchApplier(oldDexStream, (int) oldDexEntry.getSize(), patchFileStream).executeAndSaveTo(zos);
34                 }
35                 zos.closeEntry();
36             } finally {
37                 SharePatchFileUtil.closeQuietly(zos);
38             }
39         } else {
40             new DexPatchApplier(oldDexStream, (int) oldDexEntry.getSize(), patchFileStream).executeAndSaveTo(patchedDexFile);
41         }
42     } finally {
43         SharePatchFileUtil.closeQuietly(oldDexStream);
44         SharePatchFileUtil.closeQuietly(patchFileStream);
45     }
46 }

DexPatchApplier.executeAndSaveTo(OutputStream out)中会对15个dex区域进行patch操作，

针对old dex和patch dex进行合并,生成全量dex文件。

  1 public void executeAndSaveTo(OutputStream out) throws IOException {
  2     // Before executing, we should check if this patch can be applied to
  3     // old dex we passed in.
  4     // 首先old apk的签名和patchfile所携带的old apk签名是否一致，不一致则抛出异常
  5     byte[] oldDexSign = this.oldDex.computeSignature(false);
  6     if (oldDexSign == null) {
  7         throw new IOException("failed to compute old dex's signature.");
  8     }
  9 
 10     if (this.patchFile != null) {
 11         byte[] oldDexSignInPatchFile = this.patchFile.getOldDexSignature();
 12         if (CompareUtils.uArrCompare(oldDexSign, oldDexSignInPatchFile) != 0) {
 13             throw new IOException(
 14                     String.format(
 15                             "old dex signature mismatch! expected: %s, actual: %s",
 16                             Arrays.toString(oldDexSign),
 17                             Arrays.toString(oldDexSignInPatchFile)
 18                     )
 19             );
 20         }
 21     }
 22 
 23     String oldDexSignStr = Hex.toHexString(oldDexSign);
 24 
 25     // Firstly, set sections' offset after patched, sort according to their offset so that
 26     // the dex lib of aosp can calculate section size.
 27     // patchedDex是最终合成的dex，首先设定各个区域的偏移量
 28     TableOfContents patchedToc = this.patchedDex.getTableOfContents();
 29 
 30     patchedToc.header.off = 0;
 31     patchedToc.header.size = 1;
 32     patchedToc.mapList.size = 1;
 33 
 34     if (extraInfoFile == null || !extraInfoFile.isAffectedOldDex(this.oldDexSignStr)) {
 35         patchedToc.stringIds.off
 36                 = this.patchFile.getPatchedStringIdSectionOffset();
 37         patchedToc.typeIds.off
 38                 = this.patchFile.getPatchedTypeIdSectionOffset();
 39         patchedToc.typeLists.off
 40                 = this.patchFile.getPatchedTypeListSectionOffset();
 41         patchedToc.protoIds.off
 42                 = this.patchFile.getPatchedProtoIdSectionOffset();
 43         patchedToc.fieldIds.off
 44                 = this.patchFile.getPatchedFieldIdSectionOffset();
 45         patchedToc.methodIds.off
 46                 = this.patchFile.getPatchedMethodIdSectionOffset();
 47         patchedToc.classDefs.off
 48                 = this.patchFile.getPatchedClassDefSectionOffset();
 49         patchedToc.mapList.off
 50                 = this.patchFile.getPatchedMapListSectionOffset();
 51         patchedToc.stringDatas.off
 52                 = this.patchFile.getPatchedStringDataSectionOffset();
 53         patchedToc.annotations.off
 54                 = this.patchFile.getPatchedAnnotationSectionOffset();
 55         patchedToc.annotationSets.off
 56                 = this.patchFile.getPatchedAnnotationSetSectionOffset();
 57         patchedToc.annotationSetRefLists.off
 58                 = this.patchFile.getPatchedAnnotationSetRefListSectionOffset();
 59         patchedToc.annotationsDirectories.off
 60                 = this.patchFile.getPatchedAnnotationsDirectorySectionOffset();
 61         patchedToc.encodedArrays.off
 62                 = this.patchFile.getPatchedEncodedArraySectionOffset();
 63         patchedToc.debugInfos.off
 64                 = this.patchFile.getPatchedDebugInfoSectionOffset();
 65         patchedToc.codes.off
 66                 = this.patchFile.getPatchedCodeSectionOffset();
 67         patchedToc.classDatas.off
 68                 = this.patchFile.getPatchedClassDataSectionOffset();
 69         patchedToc.fileSize
 70                 = this.patchFile.getPatchedDexSize();
 71     } else {
 72        ...
 73     }
 74 
 75     Arrays.sort(patchedToc.sections);
 76 
 77     patchedToc.computeSizesFromOffsets();
 78 
 79     // Secondly, run patch algorithms according to sections' dependencies.
 80     // 对每个区域进行patch操作
 81     this.stringDataSectionPatchAlg = new StringDataSectionPatchAlgorithm(
 82             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
 83             patchedToSmallPatchedIndexMap, extraInfoFile
 84     );
 85     this.typeIdSectionPatchAlg = new TypeIdSectionPatchAlgorithm(
 86             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
 87             patchedToSmallPatchedIndexMap, extraInfoFile
 88     );
 89     this.protoIdSectionPatchAlg = new ProtoIdSectionPatchAlgorithm(
 90             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
 91             patchedToSmallPatchedIndexMap, extraInfoFile
 92     );
 93     this.fieldIdSectionPatchAlg = new FieldIdSectionPatchAlgorithm(
 94             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
 95             patchedToSmallPatchedIndexMap, extraInfoFile
 96     );
 97     this.methodIdSectionPatchAlg = new MethodIdSectionPatchAlgorithm(
 98             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
 99             patchedToSmallPatchedIndexMap, extraInfoFile
100     );
101     this.classDefSectionPatchAlg = new ClassDefSectionPatchAlgorithm(
102             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
103             patchedToSmallPatchedIndexMap, extraInfoFile
104     );
105     this.typeListSectionPatchAlg = new TypeListSectionPatchAlgorithm(
106             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
107             patchedToSmallPatchedIndexMap, extraInfoFile
108     );
109     this.annotationSetRefListSectionPatchAlg = new AnnotationSetRefListSectionPatchAlgorithm(
110             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
111             patchedToSmallPatchedIndexMap, extraInfoFile
112     );
113     this.annotationSetSectionPatchAlg = new AnnotationSetSectionPatchAlgorithm(
114             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
115             patchedToSmallPatchedIndexMap, extraInfoFile
116     );
117     this.classDataSectionPatchAlg = new ClassDataSectionPatchAlgorithm(
118             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
119             patchedToSmallPatchedIndexMap, extraInfoFile
120     );
121     this.codeSectionPatchAlg = new CodeSectionPatchAlgorithm(
122             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
123             patchedToSmallPatchedIndexMap, extraInfoFile
124     );
125     this.debugInfoSectionPatchAlg = new DebugInfoItemSectionPatchAlgorithm(
126             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
127             patchedToSmallPatchedIndexMap, extraInfoFile
128     );
129     this.annotationSectionPatchAlg = new AnnotationSectionPatchAlgorithm(
130             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
131             patchedToSmallPatchedIndexMap, extraInfoFile
132     );
133     this.encodedArraySectionPatchAlg = new StaticValueSectionPatchAlgorithm(
134             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
135             patchedToSmallPatchedIndexMap, extraInfoFile
136     );
137     this.annotationsDirectorySectionPatchAlg = new AnnotationsDirectorySectionPatchAlgorithm(
138             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
139             patchedToSmallPatchedIndexMap, extraInfoFile
140     );
141 
142     this.stringDataSectionPatchAlg.execute();
143     this.typeIdSectionPatchAlg.execute();
144     this.typeListSectionPatchAlg.execute();
145     this.protoIdSectionPatchAlg.execute();
146     this.fieldIdSectionPatchAlg.execute();
147     this.methodIdSectionPatchAlg.execute();
148     Runtime.getRuntime().gc();
149     this.annotationSectionPatchAlg.execute();
150     this.annotationSetSectionPatchAlg.execute();
151     this.annotationSetRefListSectionPatchAlg.execute();
152     this.annotationsDirectorySectionPatchAlg.execute();
153     Runtime.getRuntime().gc();
154     this.debugInfoSectionPatchAlg.execute();
155     this.codeSectionPatchAlg.execute();
156     Runtime.getRuntime().gc();
157     this.classDataSectionPatchAlg.execute();
158     this.encodedArraySectionPatchAlg.execute();
159     this.classDefSectionPatchAlg.execute();
160     Runtime.getRuntime().gc();
161 
162     // Thirdly, write header, mapList. Calculate and write patched dex's sign and checksum.
163     Dex.Section headerOut = this.patchedDex.openSection(patchedToc.header.off);
164     patchedToc.writeHeader(headerOut);
165 
166     Dex.Section mapListOut = this.patchedDex.openSection(patchedToc.mapList.off);
167     patchedToc.writeMap(mapListOut);
168 
169     this.patchedDex.writeHashes();
170 
171     // Finally, write patched dex to file.
172     this.patchedDex.writeTo(out);

每个区域的合并算法采用二路归并，在old dex的基础上对元素进行删除，增加，替换操作。

这里的算法和生成补丁的DexDiff是一个逆向的过程。

 1 private void doFullPatch(
 2         Dex.Section oldSection,
 3         int oldItemCount,
 4         int[] deletedIndices,
 5         int[] addedIndices,
 6         int[] replacedIndices
 7 ) {
 8     int deletedItemCount = deletedIndices.length;
 9     int addedItemCount = addedIndices.length;
10     int replacedItemCount = replacedIndices.length;
11     int newItemCount = oldItemCount + addedItemCount - deletedItemCount;
12 
13     int deletedItemCounter = 0;
14     int addActionCursor = 0;
15     int replaceActionCursor = 0;
16 
17     int oldIndex = 0;
18     int patchedIndex = 0;
19     while (oldIndex < oldItemCount || patchedIndex < newItemCount) {
20         if (addActionCursor < addedItemCount && addedIndices[addActionCursor] == patchedIndex) {
21             T addedItem = nextItem(patchFile.getBuffer());
22             int patchedOffset = writePatchedItem(addedItem);
23             ++addActionCursor;
24             ++patchedIndex;
25         } else
26         if (replaceActionCursor < replacedItemCount && replacedIndices[replaceActionCursor] == patchedIndex) {
27             T replacedItem = nextItem(patchFile.getBuffer());
28             int patchedOffset = writePatchedItem(replacedItem);
29             ++replaceActionCursor;
30             ++patchedIndex;
31         } else
32         if (Arrays.binarySearch(deletedIndices, oldIndex) >= 0) {
33             T skippedOldItem = nextItem(oldSection); // skip old item.
34             markDeletedIndexOrOffset(
35                     oldToFullPatchedIndexMap,
36                     oldIndex,
37                     getItemOffsetOrIndex(oldIndex, skippedOldItem)
38             );
39             ++oldIndex;
40             ++deletedItemCounter;
41         } else
42         if (Arrays.binarySearch(replacedIndices, oldIndex) >= 0) {
43             T skippedOldItem = nextItem(oldSection); // skip old item.
44             markDeletedIndexOrOffset(
45                     oldToFullPatchedIndexMap,
46                     oldIndex,
47                     getItemOffsetOrIndex(oldIndex, skippedOldItem)
48             );
49             ++oldIndex;
50         } else
51         if (oldIndex < oldItemCount) {
52             T oldItem = adjustItem(this.oldToFullPatchedIndexMap, nextItem(oldSection));
53 
54             int patchedOffset = writePatchedItem(oldItem);
55 
56             updateIndexOrOffset(
57                     this.oldToFullPatchedIndexMap,
58                     oldIndex,
59                     getItemOffsetOrIndex(oldIndex, oldItem),
60                     patchedIndex,
61                     patchedOffset
62             );
63 
64             ++oldIndex;
65             ++patchedIndex;
66         }
67     }
68 
69     if (addActionCursor != addedItemCount || deletedItemCounter != deletedItemCount
70             || replaceActionCursor != replacedItemCount
71     ) {
72         throw new IllegalStateException(
73                 String.format(
74                         "bad patch operation sequence. addCounter: %d, addCount: %d, "
75                                 + "delCounter: %d, delCount: %d, "
76                                 + "replaceCounter: %d, replaceCount:%d",
77                         addActionCursor,
78                         addedItemCount,
79                         deletedItemCounter,
80                         deletedItemCount,
81                         replaceActionCursor,
82                         replacedItemCount
83                 )
84         );
85     }
86 }

在extractDexDiffInternals调用完以后，

会调用TinkerParallelDexOptimizer.optimizeAll对生成的全量dex进行optimize操作，生成odex文件。

最终合成的文件会放到/data/data/${package_name}/tinker目录下。

到此，生成Dex过程完成。

三、加载全量Dex流程

TinkerApplication通过反射的方式将实际的app业务隔离，这样可以在热更新的时候修改实际的app内容。

在TinkerApplication中的onBaseContextAttached中会通过反射调用TinkerLoader的tryLoad加载已经合成的dex。

 1 private static final String TINKER_LOADER_METHOD   = "tryLoad";
 2 private void loadTinker() {
 3     //disable tinker, not need to install
 4     if (tinkerFlags == TINKER_DISABLE) {
 5         return;
 6     }
 7     tinkerResultIntent = new Intent();
 8     try {
 9         //reflect tinker loader, because loaderClass may be define by user!
10         Class<?> tinkerLoadClass = Class.forName(loaderClassName, false, getClassLoader());
11 
12         Method loadMethod = tinkerLoadClass.getMethod(TINKER_LOADER_METHOD, TinkerApplication.class, int.class, boolean.class);
13         Constructor<?> constructor = tinkerLoadClass.getConstructor();
14         tinkerResultIntent = (Intent) loadMethod.invoke(constructor.newInstance(), this, tinkerFlags, tinkerLoadVerifyFlag);
15     } catch (Throwable e) {
16         //has exception, put exception error code
17         ShareIntentUtil.setIntentReturnCode(tinkerResultIntent, ShareConstants.ERROR_LOAD_PATCH_UNKNOWN_EXCEPTION);
18         tinkerResultIntent.putExtra(INTENT_PATCH_EXCEPTION, e);
19     }
20 }

tryLoadPatchFilesInternal是加载Patch文件的核心函数，主要做了以下的事情：

tinkerFlag是否开启，否则不加载
tinker目录是否生成，没有则表示没有生成全量的dex，不需要重新加载
tinker目录是否生成，没有则表示没有生成全量的dex，不需要重新加载
tinker/patch.info是否存在，否则不加载
读取patch.info，读取失败则不加载
比较patchInfo的新旧版本，都为空则不加载
判断版本号是否为空，为空则不加载
判断patch version directory（//tinker/patch.info/patch-641e634c）是否存在
判断patchVersionDirectoryFile（//tinker/patch.info/patch-641e634c/patch-641e634c.apk）是否存在
checkTinkerPackage,（如tinkerId和oldTinkerId不能相等，否则不加载)
检测dex的完整性，包括dex是否全部生产，是否对dex做了优化，优化后的文件是否存在（//tinker/patch.info/patch-641e634c/dex）
同样对so res文件进行完整性检测
尝试超过3次不加载
loadTinkerJars/loadTinkerResources/

TinkerDexLoader.loadTinkerJars处理加载dex文件。

 1 // 获取PatchClassLoader 
 2 PathClassLoader classLoader = (PathClassLoader) TinkerDexLoader.class.getClassLoader();
 3 
 4 ...
 5 // 生产合法文件列表
 6 ArrayList<File> legalFiles = new ArrayList<>();
 7 
 8 final boolean isArtPlatForm = ShareTinkerInternals.isVmArt();
 9 for (ShareDexDiffPatchInfo info : dexList) {
10     //for dalvik, ignore art support dex
11     // dalvik虚拟机中，忽略掉只支持art的dex
12     if (isJustArtSupportDex(info)) {
13         continue;
14     }
15     String path = dexPath + info.realName;
16     File file = new File(path);
17 
18     if (tinkerLoadVerifyFlag) {
19         long start = System.currentTimeMillis();
20         String checkMd5 = isArtPlatForm ? info.destMd5InArt : info.destMd5InDvm;
21         if (!SharePatchFileUtil.verifyDexFileMd5(file, checkMd5)) {
22             //it is good to delete the mismatch file
23             ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_DEX_MD5_MISMATCH);
24             intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_MISMATCH_DEX_PATH,
25                 file.getAbsolutePath());
26             return false;
27         }
28         Log.i(TAG, "verify dex file:" + file.getPath() + " md5, use time: " + (System.currentTimeMillis() - start));
29     }
30     legalFiles.add(file);
31 }
32 
33 // 如果系统OTA，对这些合法dex进行优化
34 if (isSystemOTA) {
35     parallelOTAResult = true;
36     parallelOTAThrowable = null;
37     Log.w(TAG, "systemOTA, try parallel oat dexes!!!!!");
38 
39     TinkerParallelDexOptimizer.optimizeAll(
40         legalFiles, optimizeDir,
41         new TinkerParallelDexOptimizer.ResultCallback() {
42             @Override
43             public void onSuccess(File dexFile, File optimizedDir) {
44                 // Do nothing.
45             }
46             @Override
47             public void onFailed(File dexFile, File optimizedDir, Throwable thr) {
48                 parallelOTAResult = false;
49                 parallelOTAThrowable = thr;
50             }
51         }
52     );
53     if (!parallelOTAResult) {
54         Log.e(TAG, "parallel oat dexes failed");
55         intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_EXCEPTION, parallelOTAThrowable);
56         ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_PARALLEL_DEX_OPT_EXCEPTION);
57         return false;
58     }
59 }
60 
61 // 加载Dex
62 SystemClassLoaderAdder.installDexes(application, classLoader, optimizeDir, legalFiles);

SystemClassLoaderAdder.installDexes中按照安卓的版本对dex进行install，这里应该是借鉴了MultiDex里面的install做法。

另外Tinker在生成补丁阶段会生成一个test.dex，这个test.dex的作用就是用来验证dex的加载是否成功。

test.dex中含有com.tencent.tinker.loader.TinkerTestDexLoad类，该类中包含一个字段isPatch，checkDexInstall就是通过findField该字段判断是否加载成功。

 1 public static void installDexes(Application application, PathClassLoader loader, File dexOptDir, List<File> files) throws Throwable {
 2     if (!files.isEmpty()) {
 3         ClassLoader classLoader = loader;
 4         if (Build.VERSION.SDK_INT >= 24) {
 5             classLoader = AndroidNClassLoader.inject(loader, application);
 6         }
 7         //because in dalvik, if inner class is not the same classloader with it wrapper class.
 8         //it won't fail at dex2opt
 9         if (Build.VERSION.SDK_INT >= 23) {
10             V23.install(classLoader, files, dexOptDir);
11         } else if (Build.VERSION.SDK_INT >= 19) {
12             V19.install(classLoader, files, dexOptDir);
13         } else if (Build.VERSION.SDK_INT >= 14) {
14             V14.install(classLoader, files, dexOptDir);
15         } else {
16             V4.install(classLoader, files, dexOptDir);
17         }
18         //install done
19         sPatchDexCount = files.size();
20     
21         // Tinker在生成补丁阶段会生成一个test.dex，这个test.dex的作用就是用来验证dex的加载是否成功。test.dex中含有com.tencent.tinker.loader.TinkerTestDexLoad类，该类中包含一个字段isPatch，checkDexInstall就是通过findField该字段判断是否加载成功。
22         if (!checkDexInstall(classLoader)) {
23             //reset patch dex
24             SystemClassLoaderAdder.uninstallPatchDex(classLoader);
25             throw new TinkerRuntimeException(ShareConstants.CHECK_DEX_INSTALL_FAIL);
26         }
27     }
28 }

------分割线-----

在讲install具体细节之前，回顾一下具体原理。关于Android的ClassLoader体系，android中加载类一般使用的是PathClassLoader和DexClassLoader

PathClassLoader，源码注释可以看出，android使用这个类作为系统类和应用类的加载器。

/**
 * Provides a simple {@link ClassLoader} implementation that operates on a list
 * of files and directories in the local file system, but does not attempt to
 * load classes from the network. Android uses this class for its system class
 * loader and for its application class loader(s).
 */

DexClassLoader，源码注释可以看出，可以用来从.jar和.apk类型的文件内部加载classes.dex文件。

/**
 * A class loader that loads classes from {@code .jar} and {@code .apk} files
 * containing a {@code classes.dex} entry. This can be used to execute code not
 * installed as part of an application.
 *
 * <p>This class loader requires an application-private, writable directory to
 * cache optimized classes. Use {@code Context.getDir(String, int)} to create
 * such a directory: <pre>   {@code
 *   File dexOutputDir = context.getDir("dex", 0);
 * }</pre>
 *
 * <p><strong>Do not cache optimized classes on external storage.</strong>
 * External storage does not provide access controls necessary to protect your
 * application from code injection attacks.
 */

ok，到这里，大家只需要明白，Android使用PathClassLoader作为其类加载器，DexClassLoader可以从.jar和.apk类型的文件内部加载classes.dex文件就好了。

PathClassLoader和DexClassLoader都继承自BaseDexClassLoader。在BaseDexClassLoader中有如下源码：

##BaseDexClassLoader.java##
/** structured lists of path elements */
private final DexPathList pathList;

@Override
protected Class<?> findClass(String name) throws ClassNotFoundException {
    Class clazz = pathList.findClass(name);
    if (clazz == null) {
        throw new ClassNotFoundException(name);
    }
    return clazz;
}

##DexPathList.java##
/** list of dex/resource (class path) elements */
private final Element[] dexElements;
public Class findClass(String name) {
    for (Element element : dexElements) {
        DexFile dex = element.dexFile;
        if (dex != null) {
            Class clazz = dex.loadClassBinaryName(name, definingContext);
            if (clazz != null) {
                return clazz;
            }
        }
    }
    return null;
}

##DexFile.java##
public Class loadClassBinaryName(String name, ClassLoader loader) {
    return defineClass(name, loader, mCookie);
}
private native static Class defineClass(String name, ClassLoader loader, int cookie);

通俗点讲：

一个ClassLoader可以包含多个dex文件，每个dex文件是一个Element，多个dex文件排列成一个有序的数组dexElements，当找类的时候，会按顺序遍历dex文件，然后从当前遍历的dex文件中找类，如果找类则返回，如果找不到从下一个dex文件继续查找。(来自：安卓App热补丁动态修复技术介绍)

回到分割线以前：

install的做法就是，先获取BaseDexClassLoader的dexPathList对象，

然后通过dexPathList的makeDexElements函数将我们要安装的dex转化成Element[]对象，

最后将其和dexPathList的dexElements对象进行合并，就是新的Element[]对象，

因为我们添加的dex都被放在dexElements数组的最前面，所以当通过findClass来查找这个类时，就是使用的我们最新的dex里面的类。

以V19的install为例，下面的代码非常清晰的描述了实际的加载所做的事情：

 1 private static final class V19 {
 2     private static void install(ClassLoader loader, List<File> additionalClassPathEntries,
 3                                 File optimizedDirectory)
 4         throws IllegalArgumentException, IllegalAccessException,
 5         NoSuchFieldException, InvocationTargetException, NoSuchMethodException, IOException {
 6         /* The patched class loader is expected to be a descendant of
 7          * dalvik.system.BaseDexClassLoader. We modify its
 8          * dalvik.system.DexPathList pathList field to append additional DEX
 9          * file entries.
10          */
11         Field pathListField = ShareReflectUtil.findField(loader, "pathList");
12         Object dexPathList = pathListField.get(loader);
13         ArrayList<IOException> suppressedExceptions = new ArrayList<IOException>();
14         ShareReflectUtil.expandFieldArray(dexPathList, "dexElements", makeDexElements(dexPathList,
15             new ArrayList<File>(additionalClassPathEntries), optimizedDirectory,
16             suppressedExceptions));
17         if (suppressedExceptions.size() > 0) {
18             for (IOException e : suppressedExceptions) {
19                 Log.w(TAG, "Exception in makeDexElement", e);
20                 throw e;
21             }
22         }
23     }
24 }

因为android版本更新较快，不同版本里面的DexPathList等类的函数和字段都有一些变化，这也是在install的时候需要对不同版本进行适配的原因。

到此，在当前app的classloader里面就包含了我们第二步骤里面合成的全量DEX,我们在加载类的时候就能用到新的内容了。

Congratulations！！Dex的加载流程完成。

转载请标明本文来源：http://www.cnblogs.com/yyangblog/p/6249715.html
更多内容欢迎star作者的github：https://github.com/LaurenceYang/article
如果发现本文有什么问题和任何建议，也随时欢迎交流~

下一篇文章我们将对Tinker中对资源文件的热更新进行分析。

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原文地址：https://www.cnblogs.com/yyangblog/p/6249715.html