Waiting

Files
file	wait.hpp
	waiting strategies

Concepts
concept	ein::waiter
	some way to wait for a value to change

Classes
struct	ein::mwaitx
	waiter using MONITORX/MWAITX for AMD More...
struct	ein::umwait
	waiter using UMONITOR/UMWAIT for Intel More...
struct	ein::spin
	spin waiter using PAUSE More...

Functions
template<waiter W>
ein_flatten void	ein::wait_until (volatile auto *p, auto f) noexcept ein_blocking
	Wait until a predicate holds about a given memory location.
auto	ein::with_waiter (auto k) noexcept
	finds an appropriate waiter for the current CPU

Detailed Description

---

Class Documentation

ein::mwaitx

struct ein::mwaitx

waiter using MONITORX/MWAITX for AMD

Definition at line 50 of file wait.hpp.

Public Types
using	timer_t = uint64_t
Static Public Member Functions
static void	monitor (volatile void *p) noexcept
static void	mwait (uint32_t timer=0) noexcept ein_blocking
Static Public Attributes
static const bool	supported

Member Typedef Documentation

timer_t

using ein::mwaitx::timer_t = uint64_t

Definition at line 51 of file wait.hpp.

Member Function Documentation

monitor()

static void ein::mwaitx::monitor ( volatile void * p )

inlinestaticnoexcept[[always_inline]][[artificial]]

Definition at line 52 of file wait.hpp.

{ _mm_monitorx(const_cast<void*>(p),0,0); }

mwait()

static void ein::mwaitx::mwait ( uint32_t timer = 0 )

inlinestaticnoexcept[[always_inline]][[artificial]]

Definition at line 53 of file wait.hpp.

{ _mm_mwaitx(0,0,timer); }

Member Data Documentation

supported

const bool ein::mwaitx::supported

static

Definition at line 55 of file wait.hpp.

Referenced by ein::with_waiter().

ein::umwait

struct ein::umwait

waiter using UMONITOR/UMWAIT for Intel

Definition at line 60 of file wait.hpp.

Public Types
using	timer_t = uint64_t
Static Public Member Functions
static void	monitor (volatile void *p) noexcept
static uint8_t	mwait (uint32_t timer=0) noexcept ein_blocking
Static Public Attributes
static const bool	supported

Member Typedef Documentation

timer_t

using ein::umwait::timer_t = uint64_t

Definition at line 61 of file wait.hpp.

Member Function Documentation

monitor()

static void ein::umwait::monitor ( volatile void * p )

inlinestaticnoexcept[[always_inline]][[artificial]]

Definition at line 62 of file wait.hpp.

{ return _umonitor(const_cast<void*>(p)); }

mwait()

static uint8_t ein::umwait::mwait ( uint32_t timer = 0 )

inlinestaticnoexcept[[always_inline]][[artificial]]

Definition at line 63 of file wait.hpp.

{ return _umwait(1,timer); }

Member Data Documentation

supported

const bool ein::umwait::supported

static

Definition at line 65 of file wait.hpp.

Referenced by ein::with_waiter().

ein::spin

struct ein::spin

spin waiter using PAUSE

Definition at line 69 of file wait.hpp.

Public Types
using	timer_t = uint64_t
Static Public Member Functions
static void	monitor (volatile void *) noexcept
static void	mwait (uint32_t=0) noexcept ein_blocking
Static Public Attributes
static constinit bool	supported = true

Member Typedef Documentation

timer_t

using ein::spin::timer_t = uint64_t

Definition at line 70 of file wait.hpp.

Member Function Documentation

monitor()

static void ein::spin::monitor ( volatile void * )

inlinestaticnoexcept[[always_inline]][[artificial]]

Definition at line 71 of file wait.hpp.

{}

mwait()

static void ein::spin::mwait ( uint32_t = 0 )

inlinestaticnoexcept[[always_inline]][[artificial]]

Definition at line 72 of file wait.hpp.

{ _mm_pause(); }

Member Data Documentation

supported

bool ein::spin::supported = true

inlinestaticconstinit

Definition at line 74 of file wait.hpp.

Function Documentation

wait_until()

template<waiter W>

ein_flatten void ein::wait_until ( volatile auto * p, auto f )

noexcept

Wait until a predicate holds about a given memory location.

Parameters

p	pointer to data. activity on its cache line will wake us up
f	predicate to check about the pointer

Postcondition

f(p)

Definition at line 40 of file wait.hpp.

                                                                 {
  [[assume(W::supported)]];
  while (!f(p)) {
    W::monitor(p);
    if (!f(p))
      W::mwait(0);
  }
}

with_waiter()

auto ein::with_waiter ( auto k )

noexcept

finds an appropriate waiter for the current CPU

Chooses between variations of user-mode MONITOR / MWAIT. Usage:

with_waiter([]<waiter w> noexcept { ...; wait_until<w>(p,f); ... });

invokes k with a waiter as a template parameter.

Definition at line 84 of file wait.hpp.

                                  {
  if (mwaitx::supported) return k.template operator()<mwaitx>();
  else if (umwait::supported) return k.template operator()<umwait>();
  else k.template operator()<spin>();
}

References ein::mwaitx::supported, and ein::umwait::supported.