ART世界探险(13) - 初入dex2oat
dex2oat流程分析
进入整个流程之前，我们先看一下地图，大致熟悉一下我们下一步要去哪里：
主函数
dex2oat的main函数，直接是dex2oat工厂函数的封装。
int main(int argc, char** argv) {
int result = art::dex2oat(argc, argv);
// Everything was done, do an explicit exit here to avoid running Runtime destructors that take
// time (bug 10645725) unless we're a debug build or running on valgrind. Note: The Dex2Oat class
// should not destruct the runtime in this case.
if (!art::kIsDebugBuild && (RUNNING_ON_VALGRIND == 0)) {
exit(result);
}
return result;
}构造函数
我们先看一下流程图，然后对照到代码看。
dex2oat的整个逻辑是很清晰的：
首先是不得不做一个arm上的workaround，这个与我们分析的主线暂时无关，了解一下就可以了。
然后所做的事情：
- 构造Dex2oat对象
- 处理命令行参数
- 先行判断对于文件是否有写的权限
- 打印命令行参数
- 判断dex2oat的setup是否完成
- 根据是否image分别调用CompileImage或CompileApp的处理
代码里面注释很详细，可读性很好，我们看一下：
static int dex2oat(int argc, char** argv) {
b13564922();
TimingLogger timings("compiler", false, false);
Dex2Oat dex2oat(&timings);
// Parse arguments. Argument mistakes will lead to exit(EXIT_FAILURE) in UsageError.
dex2oat.ParseArgs(argc, argv);
// Check early that the result of compilation can be written
if (!dex2oat.OpenFile()) {
return EXIT_FAILURE;
}
// Print the complete line when any of the following is true:
// 1) Debug build
// 2) Compiling an image
// 3) Compiling with --host
// 4) Compiling on the host (not a target build)
// Otherwise, print a stripped command line.
if (kIsDebugBuild || dex2oat.IsImage() || dex2oat.IsHost() || !kIsTargetBuild) {
LOG(INFO) << CommandLine();
} else {
LOG(INFO) << StrippedCommandLine();
}
if (!dex2oat.Setup()) {
dex2oat.EraseOatFile();
return EXIT_FAILURE;
}
if (dex2oat.IsImage()) {
return CompileImage(dex2oat);
} else {
return CompileApp(dex2oat);
}
}
} // namespace artCompileApp
处理命令行参数等细节我们后面再补，我们先跃进到核心逻辑CompileApp中。
我们可以看到，基本上还是对于dex2oat.Compile的封装，后面都是对写文件和计时的处理。
static int CompileApp(Dex2Oat& dex2oat) {
dex2oat.Compile();
// Create the app oat.
if (!dex2oat.CreateOatFile()) {
dex2oat.EraseOatFile();
return EXIT_FAILURE;
}
// Do not close the oat file here. We might haven gotten the output file by file descriptor,
// which we would lose.
if (!dex2oat.FlushOatFile()) {
return EXIT_FAILURE;
}
// When given --host, finish early without stripping.
if (dex2oat.IsHost()) {
if (!dex2oat.FlushCloseOatFile()) {
return EXIT_FAILURE;
}
dex2oat.DumpTiming();
return EXIT_SUCCESS;
}
// Copy unstripped to stripped location, if necessary. This will implicitly flush & close the
// unstripped version. If this is given, we expect to be able to open writable files by name.
if (!dex2oat.CopyUnstrippedToStripped()) {
return EXIT_FAILURE;
}
// Flush and close the file.
if (!dex2oat.FlushCloseOatFile()) {
return EXIT_FAILURE;
}
dex2oat.DumpTiming();
return EXIT_SUCCESS;
}CompileImage
然后我们再看一下完全是一个模子里面出来的CompileImage.
static int CompileImage(Dex2Oat& dex2oat) {
dex2oat.Compile();
// Create the boot.oat.
if (!dex2oat.CreateOatFile()) {
dex2oat.EraseOatFile();
return EXIT_FAILURE;
}
// Flush and close the boot.oat. We always expect the output file by name, and it will be
// re-opened from the unstripped name.
if (!dex2oat.FlushCloseOatFile()) {
return EXIT_FAILURE;
}
// Creates the boot.art and patches the boot.oat.
if (!dex2oat.HandleImage()) {
return EXIT_FAILURE;
}
// When given --host, finish early without stripping.
if (dex2oat.IsHost()) {
dex2oat.DumpTiming();
return EXIT_SUCCESS;
}
// Copy unstripped to stripped location, if necessary.
if (!dex2oat.CopyUnstrippedToStripped()) {
return EXIT_FAILURE;
}
// FlushClose again, as stripping might have re-opened the oat file.
if (!dex2oat.FlushCloseOatFile()) {
return EXIT_FAILURE;
}
dex2oat.DumpTiming();
return EXIT_SUCCESS;
}Compile
Java不同于其它很多编译型语言的一点是在于它有ClassLoader。在做编译之前，先要对ClassLoader进行预处理。
然后，就创建一个CompilerDriver对象，并调用driver的ComileAll来完成编译。
// Create and invoke the compiler driver. This will compile all the dex files.
void Compile() {
TimingLogger::ScopedTiming t("dex2oat Compile", timings_);
compiler_phases_timings_.reset(new CumulativeLogger("compilation times"));
// Handle and ClassLoader creation needs to come after Runtime::Create
jobject class_loader = nullptr;
Thread* self = Thread::Current();
if (!boot_image_option_.empty()) {
ClassLinker* class_linker = Runtime::Current()->GetClassLinker();
OpenClassPathFiles(runtime_->GetClassPathString(), dex_files_, &class_path_files_);
ScopedObjectAccess soa(self);
// Classpath: first the class-path given.
std::vector<const DexFile*> class_path_files;
for (auto& class_path_file : class_path_files_) {
class_path_files.push_back(class_path_file.get());
}
// Store the classpath we have right now.
key_value_store_->Put(OatHeader::kClassPathKey,
OatFile::EncodeDexFileDependencies(class_path_files));
// Then the dex files we'll compile. Thus we'll resolve the class-path first.
class_path_files.insert(class_path_files.end(), dex_files_.begin(), dex_files_.end());
class_loader = class_linker->CreatePathClassLoader(self, class_path_files);
}
driver_ = new CompilerDriver(compiler_options_.get(),
verification_results_,
&method_inliner_map_,
compiler_kind_,
instruction_set_,
instruction_set_features_.get(),
image_,
image_classes_.release(),
compiled_classes_.release(),
nullptr,
thread_count_,
dump_stats_,
dump_passes_,
dump_cfg_file_name_,
compiler_phases_timings_.get(),
swap_fd_,
profile_file_);
driver_->CompileAll(class_loader, dex_files_, timings_);
}CompilerDriver的构造函数
核心逻辑还是compiler_的初始化。
看到构造需要这么多参数，我们需要对于dex2oat的命令行参数进行一个复习了，我们在前面的《细说dex2oat(1)》中曾经有过对于所有参数的介绍。
CompilerDriver::CompilerDriver(const CompilerOptions* compiler_options,
VerificationResults* verification_results,
DexFileToMethodInlinerMap* method_inliner_map,
Compiler::Kind compiler_kind,
InstructionSet instruction_set,
const InstructionSetFeatures* instruction_set_features,
bool image, std::unordered_set<std::string>* image_classes,
std::unordered_set<std::string>* compiled_classes,
std::unordered_set<std::string>* compiled_methods,
size_t thread_count, bool dump_stats, bool dump_passes,
const std::string& dump_cfg_file_name, CumulativeLogger* timer,
int swap_fd, const std::string& profile_file)
: swap_space_(swap_fd == -1 ? nullptr : new SwapSpace(swap_fd, 10 * MB)),
swap_space_allocator_(new SwapAllocator<void>(swap_space_.get())),
profile_present_(false), compiler_options_(compiler_options),
verification_results_(verification_results),
method_inliner_map_(method_inliner_map),
compiler_(Compiler::Create(this, compiler_kind)),
compiler_kind_(compiler_kind),
instruction_set_(instruction_set),
instruction_set_features_(instruction_set_features),
freezing_constructor_lock_("freezing constructor lock"),
compiled_classes_lock_("compiled classes lock"),
compiled_methods_lock_("compiled method lock"),
compiled_methods_(MethodTable::key_compare()),
non_relative_linker_patch_count_(0u),
image_(image),
image_classes_(image_classes),
classes_to_compile_(compiled_classes),
methods_to_compile_(compiled_methods),
had_hard_verifier_failure_(false),
thread_count_(thread_count),
stats_(new AOTCompilationStats),
dedupe_enabled_(true),
dump_stats_(dump_stats),
dump_passes_(dump_passes),
dump_cfg_file_name_(dump_cfg_file_name),
timings_logger_(timer),
compiler_context_(nullptr),
support_boot_image_fixup_(instruction_set != kMips && instruction_set != kMips64),
dedupe_code_("dedupe code", *swap_space_allocator_),
dedupe_src_mapping_table_("dedupe source mapping table", *swap_space_allocator_),
dedupe_mapping_table_("dedupe mapping table", *swap_space_allocator_),
dedupe_vmap_table_("dedupe vmap table", *swap_space_allocator_),
dedupe_gc_map_("dedupe gc map", *swap_space_allocator_),
dedupe_cfi_info_("dedupe cfi info", *swap_space_allocator_) {
DCHECK(compiler_options_ != nullptr);
DCHECK(verification_results_ != nullptr);
DCHECK(method_inliner_map_ != nullptr);
dex_to_dex_compiler_ = reinterpret_cast<DexToDexCompilerFn>(ArtCompileDEX);
compiler_->Init();
CHECK_EQ(image_, image_classes_.get() != nullptr);
...
}CompilerDriver::CompileAll
首先，CompilerDriver展现了一个值得我们学习的好习惯，为编译线程构造了一个线程池。
在CompilerDriver进行编译的时候，分成了两个步骤：
- PreCompile
- Compile
void CompilerDriver::CompileAll(jobject class_loader,
const std::vector<const DexFile*>& dex_files,
TimingLogger* timings) {
DCHECK(!Runtime::Current()->IsStarted());
std::unique_ptr<ThreadPool> thread_pool(
new ThreadPool("Compiler driver thread pool", thread_count_ - 1));
...
PreCompile(class_loader, dex_files, thread_pool.get(), timings);
Compile(class_loader, dex_files, thread_pool.get(), timings);
...
}CompilerDriver::PreCompile
PreCompile的步骤主要就是两个：
- 做校验
- 做类的初始化
我们将前面判断是否要做校验的部分先略过，这个PreCompile的逻辑看起来就清晰得多。
void CompilerDriver::PreCompile(jobject class_loader, const std::vector<const DexFile*>& dex_files,
ThreadPool* thread_pool, TimingLogger* timings) {
...
Verify(class_loader, dex_files, thread_pool, timings);
...
if (had_hard_verifier_failure_ && GetCompilerOptions().AbortOnHardVerifierFailure()) {
LOG(FATAL) << "Had a hard failure verifying all classes, and was asked to abort in such "
<< "situations. Please check the log.";
}
InitializeClasses(class_loader, dex_files, thread_pool, timings);
...
}CompilerDriver::Compile
针对每一个dex，调用CompileDexFile去编译。
void CompilerDriver::Compile(jobject class_loader, const std::vector<const DexFile*>& dex_files,
ThreadPool* thread_pool, TimingLogger* timings) {
for (size_t i = 0; i != dex_files.size(); ++i) {
const DexFile* dex_file = dex_files[i];
CHECK(dex_file != nullptr);
CompileDexFile(class_loader, *dex_file, dex_files, thread_pool, timings);
}
...
}CompilerDriver::CompileDexFile
上面的Compile函数是将多个dex拆成每一个dex文件的料度，而CompileDexFile再将其拆成每个类的粒度，针对每个类再调用CompileClass来进行编译。
void CompilerDriver::CompileDexFile(jobject class_loader, const DexFile& dex_file,
const std::vector<const DexFile*>& dex_files,
ThreadPool* thread_pool, TimingLogger* timings) {
TimingLogger::ScopedTiming t("Compile Dex File", timings);
ParallelCompilationManager context(Runtime::Current()->GetClassLinker(), class_loader, this,
&dex_file, dex_files, thread_pool);
context.ForAll(0, dex_file.NumClassDefs(), CompilerDriver::CompileClass, thread_count_);
}小结
最后，我们再次复习一下到目前为止学习的过程：
