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// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Tool to log the execution of the process (Chrome). Writes logs containing
// time and address of the callback being called for the first time.
// For performance reasons logs are buffered. Every thread has its own buffer
// and log file so the contention between threads is minimal. As a side-effect,
// functions called might be mentioned in many thread logs.
// A special thread is created in the process to periodically flush logs for all
// threads in case the thread had stopped before flushing its logs.
// Also note that the instrumentation code is self-activated. It begins to
// record the log data when it is called first, including the run-time startup.
// Have it in mind when modifying it, in particular do not use global objects
// with constructors as they are called during startup (too late for us).
#include <vector>
#include <sys/time.h>
#include <sys/types.h>
#include "base/callback.h"
#include "base/containers/hash_tables.h"
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "base/synchronization/lock.h"
#include "build/build_config.h"
#if !defined(OS_ANDROID)
// This is only supported on Android thanks to the fact that on Android
// processes (other than the system's zygote) don't fork.
// To make cygprofile truly work (i.e. without any deadlock) on Chrome
// platforms that use fork(), should be written in a way that
// guarantees that:
// - No lock is acquired by a foreign thread during fork(). In particular this
// means that should not perform any heap allocation (since heap
// allocators, including TCMalloc generally use locks).
// - Only uses pthread_atfork() in the whole process. Unlike POSIX
// signals, pthread_atfork() doesn't provide a way to install multiple handlers.
// Calling pthread_atfork() in would override any handler that
// could have been installed previously.
// Chrome happens to violate the first requirement at least once by having its
// process launcher thread fork. However the child process in that case, when
// it's not instrumented with cygprofile, directly calls exec(). This is safe
// since the child process doesn't try to release a lock acquired by another
// thread in the parent process which would lead to a deadlock. This problem was
// actually observed by trying to port the current version of to
// Linux.
#error This is only supported on Android.
// The following is only exposed for testing.
namespace cygprofile {
class Thread;
// Single log entry recorded for each function call.
struct LogEntry {
LogEntry(const void* address);
const timespec time;
const pid_t pid;
const pid_t tid;
const void* const address;
// Per-thread function calls log.
class ThreadLog {
// Callback invoked for flushing that can be provided for testing.
typedef base::Callback<void (std::vector<LogEntry>*)> FlushCallback;
// Used for testing.
ThreadLog(const FlushCallback& flush_callback);
// Must only be called from the thread this ThreadLog instance is watching.
void AddEntry(void* address);
// Can be called from any thread.
void TakeEntries(std::vector<LogEntry>* output);
// Flushes the provided vector of entries to a file and clears it. Note that
// this can be called from any thread.
void Flush(std::vector<LogEntry>* entries) const;
// Default implementation (that can be overridden for testing) of the method
// above.
void FlushInternal(std::vector<LogEntry>* entries) const;
// Thread identifier as Linux kernel shows it. LWP (light-weight process) is
// a unique ID of the thread in the system, unlike pthread_self() which is the
// same for fork()-ed threads.
const pid_t tid_;
// Current thread is inside the instrumentation routine.
bool in_use_;
// Callback used to flush entries.
const FlushCallback flush_callback_;
// Keeps track of all functions that have been logged on this thread so we do
// not record duplicates.
std::hash_set<void*> called_functions_;
// A lock that guards |entries_| usage between per-thread instrumentation
// routine and timer flush callback. So the contention could happen only
// during the flush, every 15 secs.
base::Lock lock_;
std::vector<LogEntry> entries_;
// Manages a list of per-thread logs.
class ThreadLogsManager {
// Used for testing. The provided callbacks are used for testing to
// synchronize the internal thread with the unit test running on the main
// thread.
ThreadLogsManager(const base::Closure& wait_callback,
const base::Closure& notify_callback);
// Can be called from any thread.
void AddLog(scoped_ptr<ThreadLog> new_log);
void StartInternalFlushThread_Locked();
// Flush thread's entry point.
void FlushAllLogsOnFlushThread();
// Used to make the internal thread sleep before each flush iteration.
const base::Closure wait_callback_;
// Used to trigger a notification when a flush happened on the internal
// thread.
const base::Closure notify_callback_;
// Protects the state below.
base::Lock lock_;
scoped_ptr<Thread> flush_thread_;
std::vector<ThreadLog*> logs_;
} // namespace cygprofile