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// 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 <limits>
#include <optional>
#include <type_traits>
#include "base/base_export.h"
#include "base/message_loop/message_pump_type.h"
#include "base/process/process_handle.h"
#include "base/threading/platform_thread_ref.h"
#include "base/time/time.h"
#include "base/trace_event/base_tracing_forward.h"
#include "base/types/strong_alias.h"
#include "build/build_config.h"
#if BUILDFLAG(IS_WIN)
#include "base/win/windows_types.h"
#elif BUILDFLAG(IS_FUCHSIA)
#include <zircon/types.h>
#elif BUILDFLAG(IS_POSIX)
#include <pthread.h>
#include <unistd.h>
#endif
#if BUILDFLAG(IS_CHROMEOS)
#include "base/feature_list.h"
#endif
namespace base {
// Used for uniquely identifying a thread.
//
// Wraps a platform-specific integer value with platform-specific size,
// guaranteed to have a maximum bitness of 64-bit. Getting a 32-bit value is
// possible only if we either know the platform-specific size (because we're in
// platform-specific code), or if we are ok with truncation of the value (e.g.
// because we are logging and the occasional false match is not catastrophic).
class BASE_EXPORT PlatformThreadId {
public:
#if BUILDFLAG(IS_WIN)
using UnderlyingType = DWORD;
#elif BUILDFLAG(IS_FUCHSIA)
using UnderlyingType = zx_koid_t;
#elif BUILDFLAG(IS_APPLE)
using UnderlyingType = uint64_t;
#elif BUILDFLAG(IS_POSIX)
using UnderlyingType = pid_t;
#endif
static_assert(std::is_integral_v<UnderlyingType>, "Always an integer value.");
constexpr PlatformThreadId() = default;
// Special templated constructor which prevents implicit conversion of the
// integer argument.
template <typename T>
explicit constexpr PlatformThreadId(T value)
requires(std::is_same_v<T, UnderlyingType>)
: value_(value) {}
static constexpr PlatformThreadId ForTest(int value) {
return PlatformThreadId(static_cast<UnderlyingType>(value));
}
// Allow conversion to u/int64_t, whether the underlying type is signed or
// not, and whether it is 32-bit or 64-bit.
explicit constexpr operator uint64_t() const {
static_assert(sizeof(uint64_t) >= sizeof(UnderlyingType));
return static_cast<uint64_t>(value_);
}
explicit constexpr operator int64_t() const {
static_assert(sizeof(int64_t) >= sizeof(UnderlyingType));
return static_cast<int64_t>(value_);
}
// Forbid conversion to u/int32_t, since we might have a 64-bit
// value -- use truncate_to_int32_for_display_only() or raw() instead.
explicit constexpr operator uint32_t() const = delete;
explicit constexpr operator int32_t() const = delete;
// Truncating getter for an int32 representation of the id.
//
// AVOID: This should only be used in cases where truncation is not
// catastrophic, e.g. displaying the thread id in traces or logs. It will
// always be preferable to display the full, untruncated thread id.
constexpr int32_t truncate_to_int32_for_display_only() const {
return static_cast<int32_t>(value_);
}
// Getter for the underlying raw value. Should only be used when
// exposing the UnderlyingType, e.g. passing into system APIs or passing into
// functions overloaded on different integer sizes like NumberToString.
constexpr UnderlyingType raw() const { return value_; }
constexpr friend auto operator<=>(const PlatformThreadId& lhs,
const PlatformThreadId& rhs) = default;
constexpr friend bool operator==(const PlatformThreadId& lhs,
const PlatformThreadId& rhs) = default;
// Allow serialising into a trace.
void WriteIntoTrace(perfetto::TracedValue&& context) const;
private:
// TODO(crbug.com/393384253): Use a system-specific invalid value, which might
// be 0, -1, or some other value from a system header.
UnderlyingType value_ = 0;
};
inline std::ostream& operator<<(std::ostream& stream,
const PlatformThreadId& id) {
return stream << id.raw();
}
// 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_;
};
static constexpr PlatformThreadId kInvalidThreadId = PlatformThreadId();
// 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 display critical threads, ie. threads critical to compositing
// and presenting the foreground content.
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();
// 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);
// 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 std::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);
static TimeDelta GetCurrentThreadRealtimePeriodForTest();
// Initializes features for this class. See `base::features::Init()`.
static void InitializeFeatures();
};
#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(ProcessId 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)
BASE_EXPORT BASE_DECLARE_FEATURE(kSetRtForDisplayThreads);
class CrossProcessPlatformThreadDelegate;
class BASE_EXPORT PlatformThreadChromeOS : public PlatformThreadLinux {
public:
// Sets a delegate which handles thread type changes for threads of another
// process. This must be externally synchronized with any call to
// SetCurrentThreadType.
static void SetCrossProcessPlatformThreadDelegate(
CrossProcessPlatformThreadDelegate* delegate);
// Initializes features for this class. See `base::features::Init()`.
static void InitializeFeatures();
// 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(ProcessId 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 std::optional<ThreadType> GetThreadTypeFromThreadId(
ProcessId process_id,
PlatformThreadId thread_id);
// DCHECKs that the caller is on the correct sequence to perform cross-process
// priority changes without races.
//
// This does not simply return a `SequenceChecker&` and let the caller do the
// check, because doing so requires an `#include` of sequence_checker.h (since
// `SequenceChecker` is an alias rather than a forward-declarable class),
// which complicates life for other base/ headers trying to avoid circular
// dependencies.
static void DcheckCrossProcessThreadPrioritySequence();
};
#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
namespace internal {
void SetCurrentThreadType(ThreadType thread_type,
MessagePumpType pump_type_hint);
void SetCurrentThreadTypeImpl(ThreadType thread_type,
MessagePumpType pump_type_hint);
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
void SetThreadTypeLinux(ProcessId process_id,
PlatformThreadId thread_id,
ThreadType thread_type,
IsViaIPC via_ipc);
#endif
#if BUILDFLAG(IS_CHROMEOS)
void SetThreadTypeChromeOS(ProcessId process_id,
PlatformThreadId thread_id,
ThreadType thread_type,
IsViaIPC via_ipc);
#endif
#if BUILDFLAG(IS_CHROMEOS)
inline constexpr auto SetThreadType = SetThreadTypeChromeOS;
#elif BUILDFLAG(IS_LINUX)
inline constexpr auto SetThreadType = SetThreadTypeLinux;
#endif
} // namespace internal
} // namespace base
#endif // BASE_THREADING_PLATFORM_THREAD_H_