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

【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：

1. Android热更新开源项目Tinker源码解析系列之一：Dex热更新
2. Android热更新开源项目Tinker源码解析系列之二:资源热更新
3. Android热更新开源项目Tinker源码解析系类之三：so热更新

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：

1. 生成补丁流程
2. 补丁包下发成功后合成全量Dex流程
3. 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。

 //gen patch
 ApkDecoder decoder = new ApkDecoder(config);
 decoder.onAllPatchesStart();
 decoder.patch(config.mOldApkFile, config.mNewApkFile);
 decoder.onAllPatchesEnd();

 //gen meta file and version file
 PatchInfo info = new PatchInfo(config);
 info.gen();

 //build patch
 PatchBuilder builder = new PatchBuilder(config);
 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。

 //check manifest change first
 manifestDecoder.patch(oldFile, newFile);

 unzipApkFiles(oldFile, newFile);

 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。

 public FileVisitResult visitFile(Path file, BasicFileAttributes attrs) throws IOException {

     Path relativePath = newApkPath.relativize(file);

     Path oldPath = oldApkPath.resolve(relativePath);

     File oldFile = null;
     //is a new file?!
     if (oldPath.toFile().exists()) {
         oldFile = oldPath.toFile();
     }
     String patternKey = relativePath.toString().replace("\\", "/");

     if (Utils.checkFileInPattern(config.mDexFilePattern, patternKey)) {
         //also treat duplicate file as unchanged
         if (Utils.checkFileInPattern(config.mResFilePattern, patternKey) && oldFile != null) {
             resDuplicateFiles.add(oldFile);
         }

         try {
             dexDecoder.patch(oldFile, file.toFile());
         } catch (Exception e) {
 //                    e.printStackTrace();
             throw new RuntimeException(e);
         }
         return FileVisitResult.CONTINUE;
     }
     if (Utils.checkFileInPattern(config.mSoFilePattern, patternKey)) {
         //also treat duplicate file as unchanged
         if (Utils.checkFileInPattern(config.mResFilePattern, patternKey) && oldFile != null) {
             resDuplicateFiles.add(oldFile);
         }
         try {
             soDecoder.patch(oldFile, file.toFile());
         } catch (Exception e) {
 //                    e.printStackTrace();
             throw new RuntimeException(e);
         }
         return FileVisitResult.CONTINUE;
     }
     if (Utils.checkFileInPattern(config.mResFilePattern, patternKey)) {
         try {
             resDecoder.patch(oldFile, file.toFile());
         } catch (Exception e) {
 //                    e.printStackTrace();
             throw new RuntimeException(e);
         }
         return FileVisitResult.CONTINUE;
     }
     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。

 excludedClassModifiedChecker.checkIfExcludedClassWasModifiedInNewDex(oldFile, newFile);
 ...
 //new add file
 if (oldFile == null || !oldFile.exists() || oldFile.length() == 0) {
     hasDexChanged = true;
     if (!config.mUsePreGeneratedPatchDex) {
         copyNewDexAndLogToDexMeta(newFile, newMd5, dexDiffOut);
         return true;
     }
 }
 ...
 // collect current old dex file and corresponding new dex file for further processing.
 oldAndNewDexFilePairList.add(new AbstractMap.SimpleEntry<>(oldFile, newFile));

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

 public boolean patch(File oldFile, File newFile) throws IOException, TinkerPatchException {
     boolean added = super.patch(oldFile, newFile);
     if (added) {
         String name = newFile.getName();
         if (addedDexFiles.contains(name)) {
             throw new TinkerPatchException("illegal dex name, dex name should be unique, dex:" + name);
         } else {
             addedDexFiles.add(name);
         }
     }
     return added;
 }

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

  private void writeResultToStream(OutputStream os) throws IOException {
     DexDataBuffer buffer = new DexDataBuffer();
     buffer.write(DexPatchFile.MAGIC);
     buffer.writeShort(DexPatchFile.CURRENT_VERSION);
     buffer.writeInt(this.patchedDexSize);
     // we will return here to write firstChunkOffset later.
     int posOfFirstChunkOffsetField = buffer.position();
     buffer.writeInt(0);
     buffer.writeInt(this.patchedStringIdsOffset);
     buffer.writeInt(this.patchedTypeIdsOffset);
     buffer.writeInt(this.patchedProtoIdsOffset);
     buffer.writeInt(this.patchedFieldIdsOffset);
     buffer.writeInt(this.patchedMethodIdsOffset);
     buffer.writeInt(this.patchedClassDefsOffset);
     buffer.writeInt(this.patchedMapListOffset);
     buffer.writeInt(this.patchedTypeListsOffset);
     buffer.writeInt(this.patchedAnnotationSetRefListItemsOffset);
     buffer.writeInt(this.patchedAnnotationSetItemsOffset);
     buffer.writeInt(this.patchedClassDataItemsOffset);
     buffer.writeInt(this.patchedCodeItemsOffset);
     buffer.writeInt(this.patchedStringDataItemsOffset);
     buffer.writeInt(this.patchedDebugInfoItemsOffset);
     buffer.writeInt(this.patchedAnnotationItemsOffset);
     buffer.writeInt(this.patchedEncodedArrayItemsOffset);
     buffer.writeInt(this.patchedAnnotationsDirectoryItemsOffset);
     buffer.write(this.oldDex.computeSignature(false));
     int firstChunkOffset = buffer.position();
     buffer.position(posOfFirstChunkOffsetField);
     buffer.writeInt(firstChunkOffset);
     buffer.position(firstChunkOffset);

     writePatchOperations(buffer, this.stringDataSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.typeIdSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.typeListSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.protoIdSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.fieldIdSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.methodIdSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.annotationSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.annotationSetSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.annotationSetRefListSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.annotationsDirectorySectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.debugInfoSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.codeSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.classDataSectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.encodedArraySectionDiffAlg.getPatchOperationList());
     writePatchOperations(buffer, this.classDefSectionDiffAlg.getPatchOperationList());

     byte[] bufferData = buffer.array();
     os.write(bufferData);
     os.flush();
 }

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。

 DexDiffPatchInternal.tryRecoverDexFiles
 BsDiffPatchInternal.tryRecoverLibraryFiles
 ResDiffPatchInternal.tryRecoverResourceFiles
 rewritePatchInfoFileWithLock

tryRecoverDexFiles调用DexDiffPatchInternal.patchDexFile，

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

 private static void patchDexFile(
         ZipFile baseApk, ZipFile patchPkg, ZipEntry oldDexEntry, ZipEntry patchFileEntry,
         ShareDexDiffPatchInfo patchInfo,  File patchedDexFile) throws IOException {
     InputStream oldDexStream = null;
     InputStream patchFileStream = null;
     try {
         oldDexStream = baseApk.getInputStream(oldDexEntry);
         patchFileStream = (patchFileEntry != null ? patchPkg.getInputStream(patchFileEntry) : null);

         final boolean isRawDexFile = SharePatchFileUtil.isRawDexFile(patchInfo.rawName);
         if (!isRawDexFile || patchInfo.isJarMode) {
             ZipOutputStream zos = null;
             try {
                 zos = new ZipOutputStream(new BufferedOutputStream(new FileOutputStream(patchedDexFile)));
                 zos.putNextEntry(new ZipEntry(ShareConstants.DEX_IN_JAR));
                 // Old dex is not a raw dex file.
                 if (!isRawDexFile) {
                     ZipInputStream zis = null;
                     try {
                         zis = new ZipInputStream(oldDexStream);
                         ZipEntry entry;
                         while ((entry = zis.getNextEntry()) != null) {
                             if (ShareConstants.DEX_IN_JAR.equals(entry.getName())) break;
                         }
                         if (entry == null) {
                             throw new TinkerRuntimeException("can't recognize zip dex format file:" + patchedDexFile.getAbsolutePath());
                         }
                         new DexPatchApplier(zis, (int) entry.getSize(), patchFileStream).executeAndSaveTo(zos);
                     } finally {
                         SharePatchFileUtil.closeQuietly(zis);
                     }
                 } else {
                     new DexPatchApplier(oldDexStream, (int) oldDexEntry.getSize(), patchFileStream).executeAndSaveTo(zos);
                 }
                 zos.closeEntry();
             } finally {
                 SharePatchFileUtil.closeQuietly(zos);
             }
         } else {
             new DexPatchApplier(oldDexStream, (int) oldDexEntry.getSize(), patchFileStream).executeAndSaveTo(patchedDexFile);
         }
     } finally {
         SharePatchFileUtil.closeQuietly(oldDexStream);
         SharePatchFileUtil.closeQuietly(patchFileStream);
     }
 }

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。

 public void executeAndSaveTo(OutputStream out) throws IOException {
     // Before executing, we should check if this patch can be applied to
     // old dex we passed in.
     // 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
     byte[] oldDexSign = this.oldDex.computeSignature(false);
     if (oldDexSign == null) {
         throw new IOException("failed to compute old dex's signature.");
     }

     if (this.patchFile != null) {
         byte[] oldDexSignInPatchFile = this.patchFile.getOldDexSignature();
         if (CompareUtils.uArrCompare(oldDexSign, oldDexSignInPatchFile) != 0) {
             throw new IOException(
                     String.format(
                             "old dex signature mismatch! expected: %s, actual: %s",
                             Arrays.toString(oldDexSign),
                             Arrays.toString(oldDexSignInPatchFile)
                     )
             );
         }
     }

     String oldDexSignStr = Hex.toHexString(oldDexSign);

     // Firstly, set sections' offset after patched, sort according to their offset so that
     // the dex lib of aosp can calculate section size.
     // patchedDex是最终合成的dex，首先设定各个区域的偏移量
     TableOfContents patchedToc = this.patchedDex.getTableOfContents();

     patchedToc.header.off = 0;
     patchedToc.header.size = 1;
     patchedToc.mapList.size = 1;

     if (extraInfoFile == null || !extraInfoFile.isAffectedOldDex(this.oldDexSignStr)) {
         patchedToc.stringIds.off
                 = this.patchFile.getPatchedStringIdSectionOffset();
         patchedToc.typeIds.off
                 = this.patchFile.getPatchedTypeIdSectionOffset();
         patchedToc.typeLists.off
                 = this.patchFile.getPatchedTypeListSectionOffset();
         patchedToc.protoIds.off
                 = this.patchFile.getPatchedProtoIdSectionOffset();
         patchedToc.fieldIds.off
                 = this.patchFile.getPatchedFieldIdSectionOffset();
         patchedToc.methodIds.off
                 = this.patchFile.getPatchedMethodIdSectionOffset();
         patchedToc.classDefs.off
                 = this.patchFile.getPatchedClassDefSectionOffset();
         patchedToc.mapList.off
                 = this.patchFile.getPatchedMapListSectionOffset();
         patchedToc.stringDatas.off
                 = this.patchFile.getPatchedStringDataSectionOffset();
         patchedToc.annotations.off
                 = this.patchFile.getPatchedAnnotationSectionOffset();
         patchedToc.annotationSets.off
                 = this.patchFile.getPatchedAnnotationSetSectionOffset();
         patchedToc.annotationSetRefLists.off
                 = this.patchFile.getPatchedAnnotationSetRefListSectionOffset();
         patchedToc.annotationsDirectories.off
                 = this.patchFile.getPatchedAnnotationsDirectorySectionOffset();
         patchedToc.encodedArrays.off
                 = this.patchFile.getPatchedEncodedArraySectionOffset();
         patchedToc.debugInfos.off
                 = this.patchFile.getPatchedDebugInfoSectionOffset();
         patchedToc.codes.off
                 = this.patchFile.getPatchedCodeSectionOffset();
         patchedToc.classDatas.off
                 = this.patchFile.getPatchedClassDataSectionOffset();
         patchedToc.fileSize
                 = this.patchFile.getPatchedDexSize();
     } else {
        ...
     }

     Arrays.sort(patchedToc.sections);

     patchedToc.computeSizesFromOffsets();

     // Secondly, run patch algorithms according to sections' dependencies.
     // 对每个区域进行patch操作
     this.stringDataSectionPatchAlg = new StringDataSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.typeIdSectionPatchAlg = new TypeIdSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.protoIdSectionPatchAlg = new ProtoIdSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.fieldIdSectionPatchAlg = new FieldIdSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.methodIdSectionPatchAlg = new MethodIdSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.classDefSectionPatchAlg = new ClassDefSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.typeListSectionPatchAlg = new TypeListSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.annotationSetRefListSectionPatchAlg = new AnnotationSetRefListSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.annotationSetSectionPatchAlg = new AnnotationSetSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.classDataSectionPatchAlg = new ClassDataSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.codeSectionPatchAlg = new CodeSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.debugInfoSectionPatchAlg = new DebugInfoItemSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.annotationSectionPatchAlg = new AnnotationSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.encodedArraySectionPatchAlg = new StaticValueSectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );
     this.annotationsDirectorySectionPatchAlg = new AnnotationsDirectorySectionPatchAlgorithm(
             patchFile, oldDex, patchedDex, oldToFullPatchedIndexMap,
             patchedToSmallPatchedIndexMap, extraInfoFile
     );

     this.stringDataSectionPatchAlg.execute();
     this.typeIdSectionPatchAlg.execute();
     this.typeListSectionPatchAlg.execute();
     this.protoIdSectionPatchAlg.execute();
     this.fieldIdSectionPatchAlg.execute();
     this.methodIdSectionPatchAlg.execute();
     Runtime.getRuntime().gc();
     this.annotationSectionPatchAlg.execute();
     this.annotationSetSectionPatchAlg.execute();
     this.annotationSetRefListSectionPatchAlg.execute();
     this.annotationsDirectorySectionPatchAlg.execute();
     Runtime.getRuntime().gc();
     this.debugInfoSectionPatchAlg.execute();
     this.codeSectionPatchAlg.execute();
     Runtime.getRuntime().gc();
     this.classDataSectionPatchAlg.execute();
     this.encodedArraySectionPatchAlg.execute();
     this.classDefSectionPatchAlg.execute();
     Runtime.getRuntime().gc();

     // Thirdly, write header, mapList. Calculate and write patched dex's sign and checksum.
     Dex.Section headerOut = this.patchedDex.openSection(patchedToc.header.off);
     patchedToc.writeHeader(headerOut);

     Dex.Section mapListOut = this.patchedDex.openSection(patchedToc.mapList.off);
     patchedToc.writeMap(mapListOut);

     this.patchedDex.writeHashes();

     // Finally, write patched dex to file.
     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。

 private void doFullPatch(
         Dex.Section oldSection,
         int oldItemCount,
         int[] deletedIndices,
         int[] addedIndices,
         int[] replacedIndices
 ) {
     int deletedItemCount = deletedIndices.length;
     int addedItemCount = addedIndices.length;
     int replacedItemCount = replacedIndices.length;
     int newItemCount = oldItemCount + addedItemCount - deletedItemCount;

     int deletedItemCounter = 0;
     int addActionCursor = 0;
     int replaceActionCursor = 0;

     int oldIndex = 0;
     int patchedIndex = 0;
     while (oldIndex < oldItemCount || patchedIndex < newItemCount) {
         if (addActionCursor < addedItemCount && addedIndices[addActionCursor] == patchedIndex) {
             T addedItem = nextItem(patchFile.getBuffer());
             int patchedOffset = writePatchedItem(addedItem);
             ++addActionCursor;
             ++patchedIndex;
         } else
         if (replaceActionCursor < replacedItemCount && replacedIndices[replaceActionCursor] == patchedIndex) {
             T replacedItem = nextItem(patchFile.getBuffer());
             int patchedOffset = writePatchedItem(replacedItem);
             ++replaceActionCursor;
             ++patchedIndex;
         } else
         if (Arrays.binarySearch(deletedIndices, oldIndex) >= 0) {
             T skippedOldItem = nextItem(oldSection); // skip old item.
             markDeletedIndexOrOffset(
                     oldToFullPatchedIndexMap,
                     oldIndex,
                     getItemOffsetOrIndex(oldIndex, skippedOldItem)
             );
             ++oldIndex;
             ++deletedItemCounter;
         } else
         if (Arrays.binarySearch(replacedIndices, oldIndex) >= 0) {
             T skippedOldItem = nextItem(oldSection); // skip old item.
             markDeletedIndexOrOffset(
                     oldToFullPatchedIndexMap,
                     oldIndex,
                     getItemOffsetOrIndex(oldIndex, skippedOldItem)
             );
             ++oldIndex;
         } else
         if (oldIndex < oldItemCount) {
             T oldItem = adjustItem(this.oldToFullPatchedIndexMap, nextItem(oldSection));

             int patchedOffset = writePatchedItem(oldItem);

             updateIndexOrOffset(
                     this.oldToFullPatchedIndexMap,
                     oldIndex,
                     getItemOffsetOrIndex(oldIndex, oldItem),
                     patchedIndex,
                     patchedOffset
             );

             ++oldIndex;
             ++patchedIndex;
         }
     }

     if (addActionCursor != addedItemCount || deletedItemCounter != deletedItemCount
             || replaceActionCursor != replacedItemCount
     ) {
         throw new IllegalStateException(
                 String.format(
                         "bad patch operation sequence. addCounter: %d, addCount: %d, "
                                 + "delCounter: %d, delCount: %d, "
                                 + "replaceCounter: %d, replaceCount:%d",
                         addActionCursor,
                         addedItemCount,
                         deletedItemCounter,
                         deletedItemCount,
                         replaceActionCursor,
                         replacedItemCount
                 )
         );
     }
 }

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。

 private static final String TINKER_LOADER_METHOD   = "tryLoad";
 private void loadTinker() {
     //disable tinker, not need to install
     if (tinkerFlags == TINKER_DISABLE) {
         return;
     }
     tinkerResultIntent = new Intent();
     try {
         //reflect tinker loader, because loaderClass may be define by user!
         Class<?> tinkerLoadClass = Class.forName(loaderClassName, false, getClassLoader());

         Method loadMethod = tinkerLoadClass.getMethod(TINKER_LOADER_METHOD, TinkerApplication.class, int.class, boolean.class);
         Constructor<?> constructor = tinkerLoadClass.getConstructor();
         tinkerResultIntent = (Intent) loadMethod.invoke(constructor.newInstance(), this, tinkerFlags, tinkerLoadVerifyFlag);
     } catch (Throwable e) {
         //has exception, put exception error code
         ShareIntentUtil.setIntentReturnCode(tinkerResultIntent, ShareConstants.ERROR_LOAD_PATCH_UNKNOWN_EXCEPTION);
         tinkerResultIntent.putExtra(INTENT_PATCH_EXCEPTION, e);
     }
 }

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。

 // 获取PatchClassLoader
 PathClassLoader classLoader = (PathClassLoader) TinkerDexLoader.class.getClassLoader();

 ...
 // 生产合法文件列表
 ArrayList<File> legalFiles = new ArrayList<>();

 final boolean isArtPlatForm = ShareTinkerInternals.isVmArt();
 for (ShareDexDiffPatchInfo info : dexList) {
     //for dalvik, ignore art support dex
     // dalvik虚拟机中，忽略掉只支持art的dex
     if (isJustArtSupportDex(info)) {
         continue;
     }
     String path = dexPath + info.realName;
     File file = new File(path);

     if (tinkerLoadVerifyFlag) {
         long start = System.currentTimeMillis();
         String checkMd5 = isArtPlatForm ? info.destMd5InArt : info.destMd5InDvm;
         if (!SharePatchFileUtil.verifyDexFileMd5(file, checkMd5)) {
             //it is good to delete the mismatch file
             ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_DEX_MD5_MISMATCH);
             intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_MISMATCH_DEX_PATH,
                 file.getAbsolutePath());
             return false;
         }
         Log.i(TAG, "verify dex file:" + file.getPath() + " md5, use time: " + (System.currentTimeMillis() - start));
     }
     legalFiles.add(file);
 }

 // 如果系统OTA，对这些合法dex进行优化
 if (isSystemOTA) {
     parallelOTAResult = true;
     parallelOTAThrowable = null;
     Log.w(TAG, "systemOTA, try parallel oat dexes!!!!!");

     TinkerParallelDexOptimizer.optimizeAll(
         legalFiles, optimizeDir,
         new TinkerParallelDexOptimizer.ResultCallback() {
             @Override
             public void onSuccess(File dexFile, File optimizedDir) {
                 // Do nothing.
             }
             @Override
             public void onFailed(File dexFile, File optimizedDir, Throwable thr) {
                 parallelOTAResult = false;
                 parallelOTAThrowable = thr;
             }
         }
     );
     if (!parallelOTAResult) {
         Log.e(TAG, "parallel oat dexes failed");
         intentResult.putExtra(ShareIntentUtil.INTENT_PATCH_EXCEPTION, parallelOTAThrowable);
         ShareIntentUtil.setIntentReturnCode(intentResult, ShareConstants.ERROR_LOAD_PATCH_VERSION_PARALLEL_DEX_OPT_EXCEPTION);
         return false;
     }
 }

 // 加载Dex
 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。

 public static void installDexes(Application application, PathClassLoader loader, File dexOptDir, List<File> files) throws Throwable {
     if (!files.isEmpty()) {
         ClassLoader classLoader = loader;
         if (Build.VERSION.SDK_INT >= 24) {
             classLoader = AndroidNClassLoader.inject(loader, application);
         }
         //because in dalvik, if inner class is not the same classloader with it wrapper class.
         //it won't fail at dex2opt
         if (Build.VERSION.SDK_INT >= 23) {
             V23.install(classLoader, files, dexOptDir);
         } else if (Build.VERSION.SDK_INT >= 19) {
             V19.install(classLoader, files, dexOptDir);
         } else if (Build.VERSION.SDK_INT >= 14) {
             V14.install(classLoader, files, dexOptDir);
         } else {
             V4.install(classLoader, files, dexOptDir);
         }
         //install done
         sPatchDexCount = files.size();

         // 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。
         if (!checkDexInstall(classLoader)) {
             //reset patch dex
             SystemClassLoaderAdder.uninstallPatchDex(classLoader);
             throw new TinkerRuntimeException(ShareConstants.CHECK_DEX_INSTALL_FAIL);
         }
     }
 }

------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：

 private static final class V19 {
     private static void install(ClassLoader loader, List<File> additionalClassPathEntries,
                                 File optimizedDirectory)
         throws IllegalArgumentException, IllegalAccessException,
         NoSuchFieldException, InvocationTargetException, NoSuchMethodException, IOException {
         /* The patched class loader is expected to be a descendant of
          * dalvik.system.BaseDexClassLoader. We modify its
          * dalvik.system.DexPathList pathList field to append additional DEX
          * file entries.
          */
         Field pathListField = ShareReflectUtil.findField(loader, "pathList");
         Object dexPathList = pathListField.get(loader);
         ArrayList<IOException> suppressedExceptions = new ArrayList<IOException>();
         ShareReflectUtil.expandFieldArray(dexPathList, "dexElements", makeDexElements(dexPathList,
             new ArrayList<File>(additionalClassPathEntries), optimizedDirectory,
             suppressedExceptions));
         if (suppressedExceptions.size() > 0) {
             for (IOException e : suppressedExceptions) {
                 Log.w(TAG, "Exception in makeDexElement", e);
                 throw e;
             }
         }
     }
 }

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。