tools/jvmti-agents/ti-alloc-sample/ti_alloc_sample.cc - LeafOS-Project/android_art - Gitiles

 // Copyright (C) 2018 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //

 #include <android-base/logging.h>

 #include <atomic>
 #include <fstream>
 #include <iostream>
 #include <istream>
 #include <iomanip>
 #include <jni.h>
 #include <jvmti.h>
 #include <limits>
 #include <map>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <sstream>
 #include <vector>

 namespace tifast {

 namespace {

 // Special art ti-version number. We will use this as a fallback if we cannot get a regular JVMTI
 // env.
 static constexpr jint kArtTiVersion = JVMTI_VERSION_1_2 | 0x40000000;

 // jthread is a typedef of jobject so we use this to allow the templates to distinguish them.
 struct jthreadContainer { jthread thread; };
 // jlocation is a typedef of jlong so use this to distinguish the less common jlong.
 struct jlongContainer { jlong val; };

 static void DeleteLocalRef(JNIEnv* env, jobject obj) {
   if (obj != nullptr && env != nullptr) {
     env->DeleteLocalRef(obj);
   }
 }

 class ScopedThreadInfo {
  public:
   ScopedThreadInfo(jvmtiEnv* jvmtienv, JNIEnv* env, jthread thread)
       : jvmtienv_(jvmtienv), env_(env), free_name_(false) {
     if (thread == nullptr) {
       info_.name = const_cast<char*>("<NULLPTR>");
     } else if (jvmtienv->GetThreadInfo(thread, &info_) != JVMTI_ERROR_NONE) {
       info_.name = const_cast<char*>("<UNKNOWN THREAD>");
     } else {
       free_name_ = true;
     }
   }

   ~ScopedThreadInfo() {
     if (free_name_) {
       jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(info_.name));
     }
     DeleteLocalRef(env_, info_.thread_group);
     DeleteLocalRef(env_, info_.context_class_loader);
   }

   const char* GetName() const {
     return info_.name;
   }

  private:
   jvmtiEnv* jvmtienv_;
   JNIEnv* env_;
   bool free_name_;
   jvmtiThreadInfo info_{};
 };

 class ScopedClassInfo {
  public:
   ScopedClassInfo(jvmtiEnv* jvmtienv, jclass c) : jvmtienv_(jvmtienv), class_(c) {}

   ~ScopedClassInfo() {
     if (class_ != nullptr) {
       jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(name_));
       jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(generic_));
       jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(file_));
       jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(debug_ext_));
     }
   }

   bool Init(bool get_generic = true) {
     if (class_ == nullptr) {
       name_ = const_cast<char*>("<NONE>");
       generic_ = const_cast<char*>("<NONE>");
       return true;
     } else {
       jvmtiError ret1 = jvmtienv_->GetSourceFileName(class_, &file_);
       jvmtiError ret2 = jvmtienv_->GetSourceDebugExtension(class_, &debug_ext_);
       char** gen_ptr = &generic_;
       if (!get_generic) {
         generic_ = nullptr;
         gen_ptr = nullptr;
       }
       return jvmtienv_->GetClassSignature(class_, &name_, gen_ptr) == JVMTI_ERROR_NONE &&
           ret1 != JVMTI_ERROR_MUST_POSSESS_CAPABILITY &&
           ret1 != JVMTI_ERROR_INVALID_CLASS &&
           ret2 != JVMTI_ERROR_MUST_POSSESS_CAPABILITY &&
           ret2 != JVMTI_ERROR_INVALID_CLASS;
     }
   }

   jclass GetClass() const {
     return class_;
   }

   const char* GetName() const {
     return name_;
   }

   const char* GetGeneric() const {
     return generic_;
   }

   const char* GetSourceDebugExtension() const {
     if (debug_ext_ == nullptr) {
       return "<UNKNOWN_SOURCE_DEBUG_EXTENSION>";
     } else {
       return debug_ext_;
     }
   }
   const char* GetSourceFileName() const {
     if (file_ == nullptr) {
       return "<UNKNOWN_FILE>";
     } else {
       return file_;
     }
   }

  private:
   jvmtiEnv* jvmtienv_;
   jclass class_;
   char* name_ = nullptr;
   char* generic_ = nullptr;
   char* file_ = nullptr;
   char* debug_ext_ = nullptr;

   friend std::ostream& operator<<(std::ostream &os, ScopedClassInfo const& m);
 };

 class ScopedMethodInfo {
  public:
   ScopedMethodInfo(jvmtiEnv* jvmtienv, JNIEnv* env, jmethodID m)
       : jvmtienv_(jvmtienv), env_(env), method_(m) {}

   ~ScopedMethodInfo() {
     DeleteLocalRef(env_, declaring_class_);
     jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(name_));
     jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(signature_));
     jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(generic_));
   }

   bool Init(bool get_generic = true) {
     if (jvmtienv_->GetMethodDeclaringClass(method_, &declaring_class_) != JVMTI_ERROR_NONE) {
       return false;
     }
     class_info_.reset(new ScopedClassInfo(jvmtienv_, declaring_class_));
     jint nlines;
     jvmtiLineNumberEntry* lines;
     jvmtiError err = jvmtienv_->GetLineNumberTable(method_, &nlines, &lines);
     if (err == JVMTI_ERROR_NONE) {
       if (nlines > 0) {
         first_line_ = lines[0].line_number;
       }
       jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(lines));
     } else if (err != JVMTI_ERROR_ABSENT_INFORMATION &&
                err != JVMTI_ERROR_NATIVE_METHOD) {
       return false;
     }
     return class_info_->Init(get_generic) &&
         (jvmtienv_->GetMethodName(method_, &name_, &signature_, &generic_) == JVMTI_ERROR_NONE);
   }

   const ScopedClassInfo& GetDeclaringClassInfo() const {
     return *class_info_;
   }

   jclass GetDeclaringClass() const {
     return declaring_class_;
   }

   const char* GetName() const {
     return name_;
   }

   const char* GetSignature() const {
     return signature_;
   }

   const char* GetGeneric() const {
     return generic_;
   }

   jint GetFirstLine() const {
     return first_line_;
   }

  private:
   jvmtiEnv* jvmtienv_;
   JNIEnv* env_;
   jmethodID method_;
   jclass declaring_class_ = nullptr;
   std::unique_ptr<ScopedClassInfo> class_info_;
   char* name_ = nullptr;
   char* signature_ = nullptr;
   char* generic_ = nullptr;
   jint first_line_ = -1;
 };

 std::ostream& operator<<(std::ostream &os, ScopedClassInfo const& c) {
   const char* generic = c.GetGeneric();
   if (generic != nullptr) {
     return os << c.GetName() << "<" << generic << ">" << " file: " << c.GetSourceFileName();
   } else {
     return os << c.GetName() << " file: " << c.GetSourceFileName();
   }
 }

 class LockedStream {
  public:
   explicit LockedStream(const std::string& filepath) {
     stream_.open(filepath, std::ofstream::out);
     if (!stream_.is_open()) {
       LOG(ERROR) << "====== JVMTI FAILED TO OPEN LOG FILE";
     }
   }
   ~LockedStream() {
     stream_.close();
   }
   void Write(const std::string& str) {
     stream_ << str;
     stream_.flush();
   }
  private:
   std::ofstream stream_;
 };

 static LockedStream* stream = nullptr;

 class UniqueStringTable {
  public:
   UniqueStringTable() = default;
   ~UniqueStringTable() = default;
   std::string Intern(const std::string& header, const std::string& key) {
     if (map_.find(key) == map_.end()) {
       map_[key] = next_index_;
       // Emit definition line.  E.g., =123,string
       stream->Write(header + std::to_string(next_index_) + "," + key + "\n");
       ++next_index_;
     }
     return std::to_string(map_[key]);
   }
  private:
   int32_t next_index_;
   std::map<std::string, int32_t> map_;
 };

 static UniqueStringTable* string_table = nullptr;

 // Formatter for the thread, type, and size of an allocation.
 static std::string formatAllocation(jvmtiEnv* jvmti,
                                     JNIEnv* jni,
                                     jthreadContainer thr,
                                     jclass klass,
                                     jlongContainer size) {
   ScopedThreadInfo sti(jvmti, jni, thr.thread);
   std::ostringstream allocation;
   allocation << "jthread[" << sti.GetName() << "]";
   ScopedClassInfo sci(jvmti, klass);
   if (sci.Init(/*get_generic=*/false)) {
     allocation << ", jclass[" << sci << "]";
   } else {
     allocation << ", jclass[TYPE UNKNOWN]";
   }
   allocation << ", size[" << size.val << ", hex: 0x" << std::hex << size.val << "]";
   return string_table->Intern("+", allocation.str());
 }

 // Formatter for a method entry on a call stack.
 static std::string formatMethod(jvmtiEnv* jvmti, JNIEnv* jni, jmethodID method_id) {
   ScopedMethodInfo smi(jvmti, jni, method_id);
   std::string method;
   if (smi.Init(/*get_generic=*/false)) {
     method = std::string(smi.GetDeclaringClassInfo().GetName()) +
         "::" + smi.GetName() + smi.GetSignature();
   } else {
     method = "ERROR";
   }
   return string_table->Intern("+", method);
 }

 static int sampling_rate;
 static int stack_depth_limit;

 static void JNICALL logVMObjectAlloc(jvmtiEnv* jvmti,
                                      JNIEnv* jni,
                                      jthread thread,
                                      jobject obj ATTRIBUTE_UNUSED,
                                      jclass klass,
                                      jlong size) {
   // Sample only once out of sampling_rate tries, and prevent recursive allocation tracking,
   static thread_local int sample_countdown = sampling_rate;
   --sample_countdown;
   if (sample_countdown != 0) {
     return;
   }

   // Guard accesses to string table and emission.
   static std::mutex mutex;
   std::lock_guard<std::mutex> lg(mutex);

   std::string record =
       formatAllocation(jvmti,
                        jni,
                        jthreadContainer{.thread = thread},
                        klass,
                        jlongContainer{.val = size});

   std::unique_ptr<jvmtiFrameInfo[]> stack_frames(new jvmtiFrameInfo[stack_depth_limit]);
   jint stack_depth;
   jvmtiError err = jvmti->GetStackTrace(thread,
                                         0,
                                         stack_depth_limit,
                                         stack_frames.get(),
                                         &stack_depth);
   if (err == JVMTI_ERROR_NONE) {
     // Emit stack frames in order from deepest in the stack to most recent.
     // This simplifies post-collection processing.
     for (int i = stack_depth - 1; i >= 0; --i) {
       record += ";" + formatMethod(jvmti, jni, stack_frames[i].method);
     }
   }
   stream->Write(string_table->Intern("=", record) + "\n");

   sample_countdown = sampling_rate;
 }

 static jvmtiEventCallbacks kLogCallbacks {
   .VMObjectAlloc = logVMObjectAlloc,
 };

 static jint SetupJvmtiEnv(JavaVM* vm, jvmtiEnv** jvmti) {
   jint res = vm->GetEnv(reinterpret_cast<void**>(jvmti), JVMTI_VERSION_1_1);
   if (res != JNI_OK || *jvmti == nullptr) {
     LOG(ERROR) << "Unable to access JVMTI, error code " << res;
     return vm->GetEnv(reinterpret_cast<void**>(jvmti), kArtTiVersion);
   }
   return res;
 }

 }  // namespace

 static jvmtiError SetupCapabilities(jvmtiEnv* jvmti) {
   jvmtiCapabilities caps{};
   caps.can_generate_vm_object_alloc_events = 1;
   caps.can_get_line_numbers = 1;
   caps.can_get_source_file_name = 1;
   caps.can_get_source_debug_extension = 1;
   return jvmti->AddCapabilities(&caps);
 }

 static bool ProcessOptions(std::string options) {
   std::string output_file_path;
   if (options.empty()) {
     static constexpr int kDefaultSamplingRate = 10;
     static constexpr int kDefaultStackDepthLimit = 50;
     static constexpr const char* kDefaultOutputFilePath = "/data/local/tmp/logstream.txt";

     sampling_rate = kDefaultSamplingRate;
     stack_depth_limit = kDefaultStackDepthLimit;
     output_file_path = kDefaultOutputFilePath;
   } else {
     // options string should contain "sampling_rate,stack_depth_limit,output_file_path".
     size_t comma_pos = options.find(',');
     if (comma_pos == std::string::npos) {
       return false;
     }
     sampling_rate = std::stoi(options.substr(0, comma_pos));
     options = options.substr(comma_pos + 1);
     comma_pos = options.find(',');
     if (comma_pos == std::string::npos) {
       return false;
     }
     stack_depth_limit = std::stoi(options.substr(0, comma_pos));
     output_file_path = options.substr(comma_pos + 1);
   }
   LOG(INFO) << "Starting allocation tracing: sampling_rate=" << sampling_rate
             << ", stack_depth_limit=" << stack_depth_limit
             << ", output_file_path=" << output_file_path;
   stream = new LockedStream(output_file_path);

   return true;
 }

 static jint AgentStart(JavaVM* vm,
                        char* options,
                        void* reserved ATTRIBUTE_UNUSED) {
   // Handle the sampling rate, depth limit, and output path, if set.
   if (!ProcessOptions(options)) {
     return JNI_ERR;
   }

   // Create the environment.
   jvmtiEnv* jvmti = nullptr;
   if (SetupJvmtiEnv(vm, &jvmti) != JNI_OK) {
     LOG(ERROR) << "Could not get JVMTI env or ArtTiEnv!";
     return JNI_ERR;
   }

   jvmtiError error = SetupCapabilities(jvmti);
   if (error != JVMTI_ERROR_NONE) {
     LOG(ERROR) << "Unable to set caps";
     return JNI_ERR;
   }

   // Add callbacks and notification.
   error = jvmti->SetEventCallbacks(&kLogCallbacks, static_cast<jint>(sizeof(kLogCallbacks)));
   if (error != JVMTI_ERROR_NONE) {
     LOG(ERROR) << "Unable to set event callbacks.";
     return JNI_ERR;
   }
   error = jvmti->SetEventNotificationMode(JVMTI_ENABLE,
                                           JVMTI_EVENT_VM_OBJECT_ALLOC,
                                           nullptr /* all threads */);
   if (error != JVMTI_ERROR_NONE) {
     LOG(ERROR) << "Unable to enable event " << JVMTI_EVENT_VM_OBJECT_ALLOC;
     return JNI_ERR;
   }

   string_table = new UniqueStringTable();

   return JNI_OK;
 }

 // Late attachment (e.g. 'am attach-agent').
 extern "C" JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM *vm, char* options, void* reserved) {
   return AgentStart(vm, options, reserved);
 }

 // Early attachment
 extern "C" JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM* jvm, char* options, void* reserved) {
   return AgentStart(jvm, options, reserved);
 }

 }  // namespace tifast
	// Copyright (C) 2018 The Android Open Source Project
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	//

	#include <android-base/logging.h>

	#include <atomic>
	#include <fstream>
	#include <iostream>
	#include <istream>
	#include <iomanip>
	#include <jni.h>
	#include <jvmti.h>
	#include <limits>
	#include <map>
	#include <memory>
	#include <mutex>
	#include <string>
	#include <sstream>
	#include <vector>

	namespace tifast {

	namespace {

	// Special art ti-version number. We will use this as a fallback if we cannot get a regular JVMTI
	// env.
	static constexpr jint kArtTiVersion = JVMTI_VERSION_1_2 \| 0x40000000;

	// jthread is a typedef of jobject so we use this to allow the templates to distinguish them.
	struct jthreadContainer { jthread thread; };
	// jlocation is a typedef of jlong so use this to distinguish the less common jlong.
	struct jlongContainer { jlong val; };

	static void DeleteLocalRef(JNIEnv* env, jobject obj) {
	if (obj != nullptr && env != nullptr) {
	env->DeleteLocalRef(obj);
	}
	}

	class ScopedThreadInfo {
	public:
	ScopedThreadInfo(jvmtiEnv* jvmtienv, JNIEnv* env, jthread thread)
	: jvmtienv_(jvmtienv), env_(env), free_name_(false) {
	if (thread == nullptr) {
	info_.name = const_cast<char*>("<NULLPTR>");
	} else if (jvmtienv->GetThreadInfo(thread, &info_) != JVMTI_ERROR_NONE) {
	info_.name = const_cast<char*>("<UNKNOWN THREAD>");
	} else {
	free_name_ = true;
	}
	}

	~ScopedThreadInfo() {
	if (free_name_) {
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(info_.name));
	}
	DeleteLocalRef(env_, info_.thread_group);
	DeleteLocalRef(env_, info_.context_class_loader);
	}

	const char* GetName() const {
	return info_.name;
	}

	private:
	jvmtiEnv* jvmtienv_;
	JNIEnv* env_;
	bool free_name_;
	jvmtiThreadInfo info_{};
	};

	class ScopedClassInfo {
	public:
	ScopedClassInfo(jvmtiEnv* jvmtienv, jclass c) : jvmtienv_(jvmtienv), class_(c) {}

	~ScopedClassInfo() {
	if (class_ != nullptr) {
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(name_));
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(generic_));
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(file_));
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(debug_ext_));
	}
	}

	bool Init(bool get_generic = true) {
	if (class_ == nullptr) {
	name_ = const_cast<char*>("<NONE>");
	generic_ = const_cast<char*>("<NONE>");
	return true;
	} else {
	jvmtiError ret1 = jvmtienv_->GetSourceFileName(class_, &file_);
	jvmtiError ret2 = jvmtienv_->GetSourceDebugExtension(class_, &debug_ext_);
	char** gen_ptr = &generic_;
	if (!get_generic) {
	generic_ = nullptr;
	gen_ptr = nullptr;
	}
	return jvmtienv_->GetClassSignature(class_, &name_, gen_ptr) == JVMTI_ERROR_NONE &&
	ret1 != JVMTI_ERROR_MUST_POSSESS_CAPABILITY &&
	ret1 != JVMTI_ERROR_INVALID_CLASS &&
	ret2 != JVMTI_ERROR_MUST_POSSESS_CAPABILITY &&
	ret2 != JVMTI_ERROR_INVALID_CLASS;
	}
	}

	jclass GetClass() const {
	return class_;
	}

	const char* GetName() const {
	return name_;
	}

	const char* GetGeneric() const {
	return generic_;
	}

	const char* GetSourceDebugExtension() const {
	if (debug_ext_ == nullptr) {
	return "<UNKNOWN_SOURCE_DEBUG_EXTENSION>";
	} else {
	return debug_ext_;
	}
	}
	const char* GetSourceFileName() const {
	if (file_ == nullptr) {
	return "<UNKNOWN_FILE>";
	} else {
	return file_;
	}
	}

	private:
	jvmtiEnv* jvmtienv_;
	jclass class_;
	char* name_ = nullptr;
	char* generic_ = nullptr;
	char* file_ = nullptr;
	char* debug_ext_ = nullptr;

	friend std::ostream& operator<<(std::ostream &os, ScopedClassInfo const& m);
	};

	class ScopedMethodInfo {
	public:
	ScopedMethodInfo(jvmtiEnv* jvmtienv, JNIEnv* env, jmethodID m)
	: jvmtienv_(jvmtienv), env_(env), method_(m) {}

	~ScopedMethodInfo() {
	DeleteLocalRef(env_, declaring_class_);
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(name_));
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(signature_));
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(generic_));
	}

	bool Init(bool get_generic = true) {
	if (jvmtienv_->GetMethodDeclaringClass(method_, &declaring_class_) != JVMTI_ERROR_NONE) {
	return false;
	}
	class_info_.reset(new ScopedClassInfo(jvmtienv_, declaring_class_));
	jint nlines;
	jvmtiLineNumberEntry* lines;
	jvmtiError err = jvmtienv_->GetLineNumberTable(method_, &nlines, &lines);
	if (err == JVMTI_ERROR_NONE) {
	if (nlines > 0) {
	first_line_ = lines[0].line_number;
	}
	jvmtienv_->Deallocate(reinterpret_cast<unsigned char*>(lines));
	} else if (err != JVMTI_ERROR_ABSENT_INFORMATION &&
	err != JVMTI_ERROR_NATIVE_METHOD) {
	return false;
	}
	return class_info_->Init(get_generic) &&
	(jvmtienv_->GetMethodName(method_, &name_, &signature_, &generic_) == JVMTI_ERROR_NONE);
	}

	const ScopedClassInfo& GetDeclaringClassInfo() const {
	return *class_info_;
	}

	jclass GetDeclaringClass() const {
	return declaring_class_;
	}

	const char* GetName() const {
	return name_;
	}

	const char* GetSignature() const {
	return signature_;
	}

	const char* GetGeneric() const {
	return generic_;
	}

	jint GetFirstLine() const {
	return first_line_;
	}

	private:
	jvmtiEnv* jvmtienv_;
	JNIEnv* env_;
	jmethodID method_;
	jclass declaring_class_ = nullptr;
	std::unique_ptr<ScopedClassInfo> class_info_;
	char* name_ = nullptr;
	char* signature_ = nullptr;
	char* generic_ = nullptr;
	jint first_line_ = -1;
	};

	std::ostream& operator<<(std::ostream &os, ScopedClassInfo const& c) {
	const char* generic = c.GetGeneric();
	if (generic != nullptr) {
	return os << c.GetName() << "<" << generic << ">" << " file: " << c.GetSourceFileName();
	} else {
	return os << c.GetName() << " file: " << c.GetSourceFileName();
	}
	}

	class LockedStream {
	public:
	explicit LockedStream(const std::string& filepath) {
	stream_.open(filepath, std::ofstream::out);
	if (!stream_.is_open()) {
	LOG(ERROR) << "====== JVMTI FAILED TO OPEN LOG FILE";
	}
	}
	~LockedStream() {
	stream_.close();
	}
	void Write(const std::string& str) {
	stream_ << str;
	stream_.flush();
	}
	private:
	std::ofstream stream_;
	};

	static LockedStream* stream = nullptr;

	class UniqueStringTable {
	public:
	UniqueStringTable() = default;
	~UniqueStringTable() = default;
	std::string Intern(const std::string& header, const std::string& key) {
	if (map_.find(key) == map_.end()) {
	map_[key] = next_index_;
	// Emit definition line. E.g., =123,string
	stream->Write(header + std::to_string(next_index_) + "," + key + "\n");
	++next_index_;
	}
	return std::to_string(map_[key]);
	}
	private:
	int32_t next_index_;
	std::map<std::string, int32_t> map_;
	};

	static UniqueStringTable* string_table = nullptr;

	// Formatter for the thread, type, and size of an allocation.
	static std::string formatAllocation(jvmtiEnv* jvmti,
	JNIEnv* jni,
	jthreadContainer thr,
	jclass klass,
	jlongContainer size) {
	ScopedThreadInfo sti(jvmti, jni, thr.thread);
	std::ostringstream allocation;
	allocation << "jthread[" << sti.GetName() << "]";
	ScopedClassInfo sci(jvmti, klass);
	if (sci.Init(/get_generic=/false)) {
	allocation << ", jclass[" << sci << "]";
	} else {
	allocation << ", jclass[TYPE UNKNOWN]";
	}
	allocation << ", size[" << size.val << ", hex: 0x" << std::hex << size.val << "]";
	return string_table->Intern("+", allocation.str());
	}

	// Formatter for a method entry on a call stack.
	static std::string formatMethod(jvmtiEnv* jvmti, JNIEnv* jni, jmethodID method_id) {
	ScopedMethodInfo smi(jvmti, jni, method_id);
	std::string method;
	if (smi.Init(/get_generic=/false)) {
	method = std::string(smi.GetDeclaringClassInfo().GetName()) +
	"::" + smi.GetName() + smi.GetSignature();
	} else {
	method = "ERROR";
	}
	return string_table->Intern("+", method);
	}

	static int sampling_rate;
	static int stack_depth_limit;

	static void JNICALL logVMObjectAlloc(jvmtiEnv* jvmti,
	JNIEnv* jni,
	jthread thread,
	jobject obj ATTRIBUTE_UNUSED,
	jclass klass,
	jlong size) {
	// Sample only once out of sampling_rate tries, and prevent recursive allocation tracking,
	static thread_local int sample_countdown = sampling_rate;
	--sample_countdown;
	if (sample_countdown != 0) {
	return;
	}

	// Guard accesses to string table and emission.
	static std::mutex mutex;
	std::lock_guard<std::mutex> lg(mutex);

	std::string record =
	formatAllocation(jvmti,
	jni,
	jthreadContainer{.thread = thread},
	klass,
	jlongContainer{.val = size});

	std::unique_ptr<jvmtiFrameInfo[]> stack_frames(new jvmtiFrameInfo[stack_depth_limit]);
	jint stack_depth;
	jvmtiError err = jvmti->GetStackTrace(thread,
	0,
	stack_depth_limit,
	stack_frames.get(),
	&stack_depth);
	if (err == JVMTI_ERROR_NONE) {
	// Emit stack frames in order from deepest in the stack to most recent.
	// This simplifies post-collection processing.
	for (int i = stack_depth - 1; i >= 0; --i) {
	record += ";" + formatMethod(jvmti, jni, stack_frames[i].method);
	}
	}
	stream->Write(string_table->Intern("=", record) + "\n");

	sample_countdown = sampling_rate;
	}

	static jvmtiEventCallbacks kLogCallbacks {
	.VMObjectAlloc = logVMObjectAlloc,
	};

	static jint SetupJvmtiEnv(JavaVM* vm, jvmtiEnv** jvmti) {
	jint res = vm->GetEnv(reinterpret_cast<void**>(jvmti), JVMTI_VERSION_1_1);
	if (res != JNI_OK \|\| *jvmti == nullptr) {
	LOG(ERROR) << "Unable to access JVMTI, error code " << res;
	return vm->GetEnv(reinterpret_cast<void**>(jvmti), kArtTiVersion);
	}
	return res;
	}

	} // namespace

	static jvmtiError SetupCapabilities(jvmtiEnv* jvmti) {
	jvmtiCapabilities caps{};
	caps.can_generate_vm_object_alloc_events = 1;
	caps.can_get_line_numbers = 1;
	caps.can_get_source_file_name = 1;
	caps.can_get_source_debug_extension = 1;
	return jvmti->AddCapabilities(&caps);
	}

	static bool ProcessOptions(std::string options) {
	std::string output_file_path;
	if (options.empty()) {
	static constexpr int kDefaultSamplingRate = 10;
	static constexpr int kDefaultStackDepthLimit = 50;
	static constexpr const char* kDefaultOutputFilePath = "/data/local/tmp/logstream.txt";

	sampling_rate = kDefaultSamplingRate;
	stack_depth_limit = kDefaultStackDepthLimit;
	output_file_path = kDefaultOutputFilePath;
	} else {
	// options string should contain "sampling_rate,stack_depth_limit,output_file_path".
	size_t comma_pos = options.find(',');
	if (comma_pos == std::string::npos) {
	return false;
	}
	sampling_rate = std::stoi(options.substr(0, comma_pos));
	options = options.substr(comma_pos + 1);
	comma_pos = options.find(',');
	if (comma_pos == std::string::npos) {
	return false;
	}
	stack_depth_limit = std::stoi(options.substr(0, comma_pos));
	output_file_path = options.substr(comma_pos + 1);
	}
	LOG(INFO) << "Starting allocation tracing: sampling_rate=" << sampling_rate
	<< ", stack_depth_limit=" << stack_depth_limit
	<< ", output_file_path=" << output_file_path;
	stream = new LockedStream(output_file_path);

	return true;
	}

	static jint AgentStart(JavaVM* vm,
	char* options,
	void* reserved ATTRIBUTE_UNUSED) {
	// Handle the sampling rate, depth limit, and output path, if set.
	if (!ProcessOptions(options)) {
	return JNI_ERR;
	}

	// Create the environment.
	jvmtiEnv* jvmti = nullptr;
	if (SetupJvmtiEnv(vm, &jvmti) != JNI_OK) {
	LOG(ERROR) << "Could not get JVMTI env or ArtTiEnv!";
	return JNI_ERR;
	}

	jvmtiError error = SetupCapabilities(jvmti);
	if (error != JVMTI_ERROR_NONE) {
	LOG(ERROR) << "Unable to set caps";
	return JNI_ERR;
	}

	// Add callbacks and notification.
	error = jvmti->SetEventCallbacks(&kLogCallbacks, static_cast<jint>(sizeof(kLogCallbacks)));
	if (error != JVMTI_ERROR_NONE) {
	LOG(ERROR) << "Unable to set event callbacks.";
	return JNI_ERR;
	}
	error = jvmti->SetEventNotificationMode(JVMTI_ENABLE,
	JVMTI_EVENT_VM_OBJECT_ALLOC,
	nullptr /* all threads */);
	if (error != JVMTI_ERROR_NONE) {
	LOG(ERROR) << "Unable to enable event " << JVMTI_EVENT_VM_OBJECT_ALLOC;
	return JNI_ERR;
	}

	string_table = new UniqueStringTable();

	return JNI_OK;
	}

	// Late attachment (e.g. 'am attach-agent').
	extern "C" JNIEXPORT jint JNICALL Agent_OnAttach(JavaVM vm, char options, void* reserved) {
	return AgentStart(vm, options, reserved);
	}

	// Early attachment
	extern "C" JNIEXPORT jint JNICALL Agent_OnLoad(JavaVM* jvm, char* options, void* reserved) {
	return AgentStart(jvm, options, reserved);
	}

	} // namespace tifast