foedus::soc::SharedPolling Class Reference

A polling-wait mechanism that can be placed in shared memory and used from multiple processes. More...

Detailed Description

A polling-wait mechanism that can be placed in shared memory and used from multiple processes.

This class automatically switches from spinning to polling with sleeps, then exponentially increases the sleep interval with some upper limit. Usually, a condition-variable packages such a functionality. BUT, we got so many troubles with glibc's bugs. A fix was pushed to upstream, but there will be many environments that still have older glibc. This class is pthread-free. No glibc versioning issue. Also, does not need signaling functionality in underlying OS/hardware, which we might not have in The Machine.

A typical usage is:

// waiter-side
while (true) {
  uint64_t demand = polling.acquire_ticket();
  // the check AFTER acquiring the ticket is required to avoid lost signal
  if (real_condition_is_met) break;
  polling.wait(demand);
}
// signaller-side
set_real_condition();  // set the real condition BEFORE signal. otherwise lost signal possible.
polling.signal();

Definition at line 63 of file shared_polling.hpp.

#include <shared_polling.hpp>

Public Member Functions
	SharedPolling ()
	SharedPolling (const SharedPolling &)=delete
SharedPolling &	operator= (const SharedPolling &)=delete
void	initialize ()
uint64_t	acquire_ticket () const
	Gives the ticket to. More...
void	wait (uint64_t demanded_ticket, uint64_t polling_spins=kDefaultPollingSpins, uint64_t max_interval_us=kDefaultPollingMaxIntervalUs) const
	Unconditionally wait for signal. More...
bool	timedwait (uint64_t demanded_ticket, uint64_t timeout_microsec, uint64_t polling_spins=kDefaultPollingSpins, uint64_t max_interval_us=kDefaultPollingMaxIntervalUs) const
	Wait for signal up to the given timeout. More...
void	signal ()
	Signal it to let waiters exit. More...

Constructor & Destructor Documentation

foedus::soc::SharedPolling::SharedPolling ( )

inline

Definition at line 65 of file shared_polling.hpp.

References initialize().

{ initialize(); }

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foedus::soc::SharedPolling::SharedPolling ( const SharedPolling &  )

delete

Member Function Documentation

uint64_t foedus::soc::SharedPolling::acquire_ticket

(

)

const

Gives the ticket to.

This method takes an acquire fence after getting the ticket. The waiter should check the real condition variable after calling this method to avoid lost signal.

Definition at line 105 of file shared_polling.cpp.

References foedus::assorted::memory_fence_acq_rel().

Referenced by foedus::xct::XctManagerPimpl::advance_current_global_epoch(), foedus::xct::XctManagerPimpl::handle_epoch_chime(), foedus::snapshot::SnapshotManagerPimpl::handle_snapshot_child(), foedus::savepoint::SavepointManagerPimpl::savepoint_main(), foedus::snapshot::SnapshotManagerPimpl::sleep_a_while(), foedus::savepoint::SavepointManagerPimpl::take_savepoint(), foedus::savepoint::SavepointManagerPimpl::take_savepoint_after_snapshot(), foedus::snapshot::SnapshotManagerPimpl::trigger_snapshot_immediate(), foedus::soc::SharedRendezvous::wait(), foedus::thread::ImpersonateSession::wait(), foedus::soc::SharedRendezvous::wait_for(), foedus::thread::ImpersonateSession::wait_for(), foedus::xct::XctManagerPimpl::wait_for_current_global_epoch(), and foedus::log::LogManagerPimpl::wait_until_durable().

                                             {
  uint64_t ret = cur_ticket_ + 1ULL;
  assorted::memory_fence_acq_rel();
  return ret;
}

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void foedus::soc::SharedPolling::initialize

(

)

Definition at line 32 of file shared_polling.cpp.

References foedus::assorted::memory_fence_acq_rel().

Referenced by foedus::log::MetaLogControlBlock::initialize(), foedus::savepoint::SavepointManagerControlBlock::initialize(), foedus::soc::SharedRendezvous::initialize(), foedus::xct::XctManagerControlBlock::initialize(), foedus::log::LogManagerControlBlock::initialize(), foedus::thread::ThreadControlBlock::initialize(), foedus::log::LoggerControlBlock::initialize(), foedus::snapshot::SnapshotManagerControlBlock::initialize(), and SharedPolling().

                               {
  cur_ticket_ = 0;
  assorted::memory_fence_acq_rel();
}

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SharedPolling& foedus::soc::SharedPolling::operator= ( const SharedPolling &  )

delete

void foedus::soc::SharedPolling::signal

(

)

Signal it to let waiters exit.

This method first takes a release fence to avoid lost signal. The signaller should set the real condition variable before calling this method to avoid lost signal.

Definition at line 100 of file shared_polling.cpp.

References foedus::assorted::memory_fence_acq_rel(), and foedus::soc::ugly_atomic_inc().

Referenced by foedus::log::LogManagerPimpl::announce_new_durable_global_epoch(), foedus::xct::XctManagerPimpl::handle_epoch_chime(), foedus::snapshot::SnapshotManagerPimpl::handle_snapshot_triggered(), foedus::log::LogManagerPimpl::refresh_global_durable_epoch(), foedus::savepoint::SavepointManagerPimpl::savepoint_main(), foedus::soc::SharedRendezvous::signal(), foedus::savepoint::SavepointManagerPimpl::take_savepoint(), foedus::savepoint::SavepointManagerPimpl::take_savepoint_after_snapshot(), foedus::thread::ThreadRef::try_impersonate(), foedus::log::MetaLogger::uninitialize_once(), foedus::xct::XctManagerPimpl::uninitialize_once(), foedus::savepoint::SavepointManagerPimpl::uninitialize_once(), foedus::thread::ThreadPimpl::uninitialize_once(), foedus::snapshot::SnapshotManagerPimpl::wakeup(), foedus::xct::XctManagerPimpl::wakeup_epoch_chime_thread(), and foedus::snapshot::SnapshotManagerControlBlock::wakeup_snapshot_children().

                           {
  assorted::memory_fence_acq_rel();  // well, atomic op implies a full barrier, but to make sure.
  ugly_atomic_inc(&cur_ticket_);
}

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bool foedus::soc::SharedPolling::timedwait	(	uint64_t	demanded_ticket,
		uint64_t	timeout_microsec,
		uint64_t	polling_spins = kDefaultPollingSpins,
		uint64_t	max_interval_us = kDefaultPollingMaxIntervalUs
	)		const

Wait for signal up to the given timeout.

Parameters

[in]	demanded_ticket	returns when cur_ticket_ becomes this value or larger.
[in]	timeout_microsec	timeout in microsec
[in]	polling_spins	we stop spinning and switch to sleeps after this number of spins
[in]	max_interval_us	the sleep interval exponentially grows up to this value in microsec.

Returns

whether this thread received a signal

Definition at line 63 of file shared_polling.cpp.

References foedus::soc::get_now_microsec(), and foedus::soc::kInitialPollingIntervalUs.

Referenced by foedus::xct::XctManagerPimpl::handle_epoch_chime(), foedus::snapshot::SnapshotManagerPimpl::handle_snapshot_child(), foedus::savepoint::SavepointManagerPimpl::savepoint_main(), foedus::snapshot::SnapshotManagerPimpl::sleep_a_while(), foedus::snapshot::SnapshotManagerPimpl::trigger_snapshot_immediate(), foedus::thread::ImpersonateSession::wait(), foedus::soc::SharedRendezvous::wait_for(), foedus::thread::ImpersonateSession::wait_for(), foedus::xct::XctManagerPimpl::wait_for_current_global_epoch(), and foedus::log::LogManagerPimpl::wait_until_durable().

                                  {
  if (cur_ticket_ >= demanded_ticket) {
    return true;
  }
  uint64_t start_us = get_now_microsec();
  uint64_t end_us = start_us + timeout_microsec;  // might overflow as a rare case, but not an issue
  spin_poll(demanded_ticket, polling_spins);

  uint64_t interval_us = kInitialPollingIntervalUs;
  while (cur_ticket_ < demanded_ticket) {
    uint64_t now_us = get_now_microsec();
    if (now_us > end_us) {
      return false;  // ah, oh, timeout
    }
    std::this_thread::sleep_for(std::chrono::microseconds(interval_us));
    interval_us = std::min<uint64_t>(interval_us * 2ULL, max_interval_us);
  }
  return true;
}

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void foedus::soc::SharedPolling::wait	(	uint64_t	demanded_ticket,
		uint64_t	polling_spins = kDefaultPollingSpins,
		uint64_t	max_interval_us = kDefaultPollingMaxIntervalUs
	)		const

Unconditionally wait for signal.

Parameters

[in]	demanded_ticket	returns when cur_ticket_ becomes this value or larger.
[in]	polling_spins	we stop spinning and switch to sleeps after this number of spins
[in]	max_interval_us	the sleep interval exponentially grows up to this value in microsec.

Definition at line 42 of file shared_polling.cpp.

References foedus::soc::kInitialPollingIntervalUs.

Referenced by foedus::xct::XctManagerPimpl::advance_current_global_epoch(), foedus::savepoint::SavepointManagerPimpl::take_savepoint(), foedus::savepoint::SavepointManagerPimpl::take_savepoint_after_snapshot(), foedus::soc::SharedRendezvous::wait(), foedus::xct::XctManagerPimpl::wait_for_current_global_epoch(), and foedus::log::LogManagerPimpl::wait_until_durable().

                                  {
  if (cur_ticket_ >= demanded_ticket) {
    return;
  }
  spin_poll(demanded_ticket, polling_spins);

  uint64_t interval_us = kInitialPollingIntervalUs;
  while (cur_ticket_ < demanded_ticket) {
    std::this_thread::sleep_for(std::chrono::microseconds(interval_us));
    interval_us = std::min<uint64_t>(interval_us * 2ULL, max_interval_us);
  }
}

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---

The documentation for this class was generated from the following files:

• /home/shino/foedus_code/foedus-core/include/foedus/soc/shared_polling.hpp
• /home/shino/foedus_code/foedus-core/src/foedus/soc/shared_polling.cpp