tor-browser

platform_thread.h (15724B)

---

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// WARNING: You should *NOT* be using this class directly.  PlatformThread is
// the low-level platform-specific abstraction to the OS's threading interface.
// You should instead be using a message-loop driven Thread, see thread.h.

#ifndef BASE_THREADING_PLATFORM_THREAD_H_
#define BASE_THREADING_PLATFORM_THREAD_H_

#include <stddef.h>

#include <iosfwd>
#include <type_traits>

#include "base/base_export.h"
#include "base/message_loop/message_pump_type.h"
#include "base/process/process_handle.h"
#include "base/sequence_checker_impl.h"
#include "base/threading/platform_thread_ref.h"
#include "base/time/time.h"
#include "base/types/strong_alias.h"
#include "build/build_config.h"
#include "build/chromeos_buildflags.h"
#include "third_party/abseil-cpp/absl/types/optional.h"

#if BUILDFLAG(IS_WIN)
#include "base/win/windows_types.h"
#elif BUILDFLAG(IS_FUCHSIA)
#include <zircon/types.h>
#elif BUILDFLAG(IS_APPLE)
#include <mach/mach_types.h>
#elif BUILDFLAG(IS_POSIX)
#include <pthread.h>
#include <unistd.h>
#endif

namespace base {

// Used for logging. Always an integer value.
#if BUILDFLAG(IS_WIN)
typedef DWORD PlatformThreadId;
#elif BUILDFLAG(IS_FUCHSIA)
typedef zx_handle_t PlatformThreadId;
#elif BUILDFLAG(IS_APPLE)
typedef mach_port_t PlatformThreadId;
#elif BUILDFLAG(IS_POSIX)
typedef pid_t PlatformThreadId;
#endif
static_assert(std::is_integral_v<PlatformThreadId>, "Always an integer value.");

// Used to operate on threads.
class PlatformThreadHandle {
public:
#if BUILDFLAG(IS_WIN)
 typedef void* Handle;
#elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
 typedef pthread_t Handle;
#endif

 constexpr PlatformThreadHandle() : handle_(0) {}

 explicit constexpr PlatformThreadHandle(Handle handle) : handle_(handle) {}

 bool is_equal(const PlatformThreadHandle& other) const {
   return handle_ == other.handle_;
 }

 bool is_null() const {
   return !handle_;
 }

 Handle platform_handle() const {
   return handle_;
 }

private:
 Handle handle_;
};

const PlatformThreadId kInvalidThreadId(0);

// Valid values for `thread_type` of Thread::Options, SimpleThread::Options,
// and SetCurrentThreadType(), listed in increasing order of importance.
//
// It is up to each platform-specific implementation what these translate to.
// Callers should avoid setting different ThreadTypes on different platforms
// (ifdefs) at all cost, instead the platform differences should be encoded in
// the platform-specific implementations. Some implementations may treat
// adjacent ThreadTypes in this enum as equivalent.
//
// Reach out to //base/task/OWNERS (scheduler-dev@chromium.org) before changing
// thread type assignments in your component, as such decisions affect the whole
// of Chrome.
//
// Refer to PlatformThreadTest.SetCurrentThreadTypeTest in
// platform_thread_unittest.cc for the most up-to-date state of each platform's
// handling of ThreadType.
enum class ThreadType : int {
 // Suitable for threads that have the least urgency and lowest priority, and
 // can be interrupted or delayed by other types.
 kBackground,
 // Suitable for threads that are less important than normal type, and can be
 // interrupted or delayed by threads with kDefault type.
 kUtility,
 // Suitable for threads that produce user-visible artifacts but aren't
 // latency sensitive. The underlying platform will try to be economic
 // in its usage of resources for this thread, if possible.
 kResourceEfficient,
 // Default type. The thread priority or quality of service will be set to
 // platform default. In Chrome, this is suitable for handling user
 // interactions (input), only display and audio can get a higher priority.
 kDefault,
 // Suitable for threads which are critical to compositing the foreground
 // content.
 kCompositing,
 // Suitable for display critical threads.
 kDisplayCritical,
 // Suitable for low-latency, glitch-resistant audio.
 kRealtimeAudio,
 kMaxValue = kRealtimeAudio,
};

// Cross-platform mapping of physical thread priorities. Used by tests to verify
// the underlying effects of SetCurrentThreadType.
enum class ThreadPriorityForTest : int {
 kBackground,
 kUtility,
 kResourceEfficient,
 kNormal,
 kCompositing,
 kDisplay,
 kRealtimeAudio,
 kMaxValue = kRealtimeAudio,
};

// A namespace for low-level thread functions.
class BASE_EXPORT PlatformThreadBase {
public:
 // Implement this interface to run code on a background thread.  Your
 // ThreadMain method will be called on the newly created thread.
 class BASE_EXPORT Delegate {
  public:
   virtual void ThreadMain() = 0;

#if BUILDFLAG(IS_APPLE)
   // TODO: Move this to the PlatformThreadApple class.
   // The interval at which the thread expects to have work to do. Zero if
   // unknown. (Example: audio buffer duration for real-time audio.) Is used to
   // optimize the thread real-time behavior. Is called on the newly created
   // thread before ThreadMain().
   virtual TimeDelta GetRealtimePeriod();
#endif

  protected:
   virtual ~Delegate() = default;
 };

 PlatformThreadBase() = delete;
 PlatformThreadBase(const PlatformThreadBase&) = delete;
 PlatformThreadBase& operator=(const PlatformThreadBase&) = delete;

 // Gets the current thread id, which may be useful for logging purposes.
 static PlatformThreadId CurrentId();

 // Gets the current thread reference, which can be used to check if
 // we're on the right thread quickly.
 static PlatformThreadRef CurrentRef();

 // Get the handle representing the current thread. On Windows, this is a
 // pseudo handle constant which will always represent the thread using it and
 // hence should not be shared with other threads nor be used to differentiate
 // the current thread from another.
 static PlatformThreadHandle CurrentHandle();

 // Yield the current thread so another thread can be scheduled.
 //
 // Note: this is likely not the right call to make in most situations. If this
 // is part of a spin loop, consider base::Lock, which likely has better tail
 // latency. Yielding the thread has different effects depending on the
 // platform, system load, etc., and can result in yielding the CPU for less
 // than 1us, or many tens of ms.
 static void YieldCurrentThread();

 // Sleeps for the specified duration (real-time; ignores time overrides).
 // Note: The sleep duration may be in base::Time or base::TimeTicks, depending
 // on platform. If you're looking to use this in unit tests testing delayed
 // tasks, this will be unreliable - instead, use
 // base::test::TaskEnvironment with MOCK_TIME mode.
 static void Sleep(base::TimeDelta duration);

 // Sets the thread name visible to debuggers/tools. This will try to
 // initialize the context for current thread unless it's a WorkerThread.
 static void SetName(const std::string& name);

 // Gets the thread name, if previously set by SetName.
 static const char* GetName();

#if !defined(MOZ_SANDBOX)
 // Creates a new thread.  The `stack_size` parameter can be 0 to indicate
 // that the default stack size should be used.  Upon success,
 // `*thread_handle` will be assigned a handle to the newly created thread,
 // and `delegate`'s ThreadMain method will be executed on the newly created
 // thread.
 // NOTE: When you are done with the thread handle, you must call Join to
 // release system resources associated with the thread.  You must ensure that
 // the Delegate object outlives the thread.
 static bool Create(size_t stack_size,
                    Delegate* delegate,
                    PlatformThreadHandle* thread_handle) {
   return CreateWithType(stack_size, delegate, thread_handle,
                         ThreadType::kDefault);
 }

 // CreateWithType() does the same thing as Create() except the priority and
 // possibly the QoS of the thread is set based on `thread_type`.
 // `pump_type_hint` must be provided if the thread will be using a
 // MessagePumpForUI or MessagePumpForIO as this affects the application of
 // `thread_type`.
 static bool CreateWithType(
     size_t stack_size,
     Delegate* delegate,
     PlatformThreadHandle* thread_handle,
     ThreadType thread_type,
     MessagePumpType pump_type_hint = MessagePumpType::DEFAULT);

 // CreateNonJoinable() does the same thing as Create() except the thread
 // cannot be Join()'d.  Therefore, it also does not output a
 // PlatformThreadHandle.
 static bool CreateNonJoinable(size_t stack_size, Delegate* delegate);

 // CreateNonJoinableWithType() does the same thing as CreateNonJoinable()
 // except the type of the thread is set based on `type`. `pump_type_hint` must
 // be provided if the thread will be using a MessagePumpForUI or
 // MessagePumpForIO as this affects the application of `thread_type`.
 static bool CreateNonJoinableWithType(
     size_t stack_size,
     Delegate* delegate,
     ThreadType thread_type,
     MessagePumpType pump_type_hint = MessagePumpType::DEFAULT);
#endif

 // Joins with a thread created via the Create function.  This function blocks
 // the caller until the designated thread exits.  This will invalidate
 // `thread_handle`.
 static void Join(PlatformThreadHandle thread_handle);

 // Detaches and releases the thread handle. The thread is no longer joinable
 // and `thread_handle` is invalidated after this call.
 static void Detach(PlatformThreadHandle thread_handle);

 // Returns true if SetCurrentThreadType() should be able to change the type
 // of a thread in current process from `from` to `to`.
 static bool CanChangeThreadType(ThreadType from, ThreadType to);

 // Declares the type of work running on the current thread. This will affect
 // things like thread priority and thread QoS (Quality of Service) to the best
 // of the current platform's abilities.
 static void SetCurrentThreadType(ThreadType thread_type);

 // Get the last `thread_type` set by SetCurrentThreadType, no matter if the
 // underlying priority successfully changed or not.
 static ThreadType GetCurrentThreadType();

 // Returns a realtime period provided by `delegate`.
 static TimeDelta GetRealtimePeriod(Delegate* delegate);

 // Returns the override of task leeway if any.
 static absl::optional<TimeDelta> GetThreadLeewayOverride();

 // Returns the default thread stack size set by chrome. If we do not
 // explicitly set default size then returns 0.
 static size_t GetDefaultThreadStackSize();

 static ThreadPriorityForTest GetCurrentThreadPriorityForTest();

 protected:
 static void SetNameCommon(const std::string& name);
};

#if BUILDFLAG(IS_APPLE)
class BASE_EXPORT PlatformThreadApple : public PlatformThreadBase {
public:
 // Stores the period value in TLS.
 static void SetCurrentThreadRealtimePeriodValue(TimeDelta realtime_period);

 // Signals that the feature list has been initialized which allows to check
 // the feature's value now and initialize state. This prevents race
 // conditions where the feature is being checked while it is being
 // initialized, which can cause a crash.
 static void InitFeaturesPostFieldTrial();
};
#endif  // BUILDFLAG(IS_APPLE)

#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
class ThreadTypeDelegate;
using IsViaIPC = base::StrongAlias<class IsViaIPCTag, bool>;

class BASE_EXPORT PlatformThreadLinux : public PlatformThreadBase {
public:
 static constexpr struct sched_param kRealTimeAudioPrio = {8};
 static constexpr struct sched_param kRealTimeDisplayPrio = {6};

 // Sets a delegate which handles thread type changes for this process. This
 // must be externally synchronized with any call to SetCurrentThreadType.
 static void SetThreadTypeDelegate(ThreadTypeDelegate* delegate);

 // Toggles a specific thread's type at runtime. This can be used to
 // change the priority of a thread in a different process and will fail
 // if the calling process does not have proper permissions. The
 // SetCurrentThreadType() function above is preferred in favor of
 // security but on platforms where sandboxed processes are not allowed to
 // change priority this function exists to allow a non-sandboxed process
 // to change the priority of sandboxed threads for improved performance.
 // Warning: Don't use this for a main thread because that will change the
 // whole thread group's (i.e. process) priority.
 static void SetThreadType(PlatformThreadId process_id,
                           PlatformThreadId thread_id,
                           ThreadType thread_type,
                           IsViaIPC via_ipc);

 // For a given thread id and thread type, setup the cpuset and schedtune
 // CGroups for the thread.
 static void SetThreadCgroupsForThreadType(PlatformThreadId thread_id,
                                           ThreadType thread_type);

 // Determine if thread_id is a background thread by looking up whether
 // it is in the urgent or non-urgent cpuset
 static bool IsThreadBackgroundedForTest(PlatformThreadId thread_id);
};
#endif  // BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)

#if BUILDFLAG(IS_CHROMEOS)

class BASE_EXPORT PlatformThreadChromeOS : public PlatformThreadLinux {
public:
 // Signals that the feature list has been initialized. Used for preventing
 // race conditions and crashes, see comments in PlatformThreadApple.
 static void InitFeaturesPostFieldTrial();

 // Toggles a specific thread's type at runtime. This is the ChromeOS-specific
 // version and includes Linux's functionality but does slightly more. See
 // PlatformThreadLinux's SetThreadType() header comment for Linux details.
 static void SetThreadType(PlatformThreadId process_id,
                           PlatformThreadId thread_id,
                           ThreadType thread_type,
                           IsViaIPC via_ipc);

 // Returns true if the feature for backgrounding of threads is enabled.
 static bool IsThreadsBgFeatureEnabled();

 // Returns true if the feature for setting display threads to RT is enabled.
 static bool IsDisplayThreadsRtFeatureEnabled();

 // Set a specific thread as backgrounded. This is called when the process
 // moves to and from the background and changes have to be made to each of its
 // thread's scheduling attributes.
 static void SetThreadBackgrounded(ProcessId process_id,
                                   PlatformThreadId thread_id,
                                   bool backgrounded);

 // Returns the thread type of a thread given its thread id.
 static absl::optional<ThreadType> GetThreadTypeFromThreadId(
     ProcessId process_id,
     PlatformThreadId thread_id);

 // Returns a SequenceChecker which should be used to verify that all
 // cross-process priority changes are performed without races.
 static SequenceCheckerImpl& GetCrossProcessThreadPrioritySequenceChecker();
};
#endif  // BUILDFLAG(IS_CHROMEOS)

// Alias to the correct platform-specific class based on preprocessor directives
#if BUILDFLAG(IS_APPLE)
using PlatformThread = PlatformThreadApple;
#elif BUILDFLAG(IS_CHROMEOS)
using PlatformThread = PlatformThreadChromeOS;
#elif BUILDFLAG(IS_LINUX)
using PlatformThread = PlatformThreadLinux;
#else
using PlatformThread = PlatformThreadBase;
#endif

#if !defined(MOZ_SANDBOX)
namespace internal {

void SetCurrentThreadType(ThreadType thread_type,
                         MessagePumpType pump_type_hint);

void SetCurrentThreadTypeImpl(ThreadType thread_type,
                             MessagePumpType pump_type_hint);

}  // namespace internal
#endif

}  // namespace base

#endif  // BASE_THREADING_PLATFORM_THREAD_H_