Art下DexClassLoader将dex转化为oat文件格式的过程

标签：android   art   

经过看源码DexClassLoader最终会调用DexFile类中的native函数openDexFileNative。

下面来看看openDexFileNative函数做了什么。

openDexFileNative函数在art\runtime\native\dalvik_system_DexFile.cc文件中下面的代码导出了openDexFileNative符号。

static JNINativeMethod gMethods[] = {
  NATIVE_METHOD(DexFile, closeDexFile, "(I)V"),
  NATIVE_METHOD(DexFile, defineClassNative, "(Ljava/lang/String;Ljava/lang/ClassLoader;I)Ljava/lang/Class;"),
  NATIVE_METHOD(DexFile, getClassNameList, "(I)[Ljava/lang/String;"),
  NATIVE_METHOD(DexFile, isDexOptNeeded, "(Ljava/lang/String;)Z"),
  NATIVE_METHOD(DexFile, openDexFileNative, "(Ljava/lang/String;Ljava/lang/String;I)I"),
};

在DexFile_openDexFileNative函数中，首先调用DexFile::GetChecksum函数获得了zip文件或dex文件的校验和，如果获得校验和成功将校验和保存在局部变量dex_location_checksum中。

DexFile::GetChecksum(dex_location, &dex_location_checksum)

std::string oat_location(outputName.c_str());
dex_file = linker->FindOrCreateOatFileForDexLocation(dex_location, dex_location_checksum, oat_location);

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

ClassLinker::FindOrCreateOatFileForDexLocation函数调用了ClassLinker::FindOrCreateOatFileForDexLocationLocked函数。

return FindOrCreateOatFileForDexLocationLocked(dex_location, dex_location_checksum, oat_location);

通过调用ClassLinker::FindDexFileInOatLocation函数判断dex文件是否已经优化为oat文件。

// Check if we already have an up-to-date output file
const DexFile* dex_file = FindDexFileInOatLocation(dex_location,
                                                     dex_location_checksum,
                                                     oat_location);

GenerateOatFile(dex_location, scoped_flock.GetFile().Fd(), oat_location)

// fork and exec dex2oat
pid_t pid = fork();

    execl(dex2oat, dex2oat,
          "--runtime-arg", "-Xms64m",
          "--runtime-arg", "-Xmx64m",
          "--runtime-arg", "-classpath",
          "--runtime-arg", class_path,
          "--runtime-arg", oat_compiler_filter_option,
#if !defined(ART_TARGET)
          "--host",
#endif
          boot_image_option,
          dex_file_option,
          oat_fd_option,
          oat_location_option,
          NULL);

const DexFile* result = oat_dex_file->OpenDexFile();

至此，完成了dex到oat的转换。

Art下DexClassLoader将dex转化为oat文件格式的过程

标签：android   art   

原文地址：http://blog.csdn.net/zylc369/article/details/39450509