seastar::gate Class Reference

Detailed Description

Facility to stop new requests, and to tell when existing requests are done.

When stopping a service that serves asynchronous requests, we are faced with two problems: preventing new requests from coming in, and knowing when existing requests have completed. The gate class provides a solution.

Examples

closeable_test.cc.

#include <seastar/core/gate.hh>

Classes
class	holder

Public Member Functions
	gate (const gate &)=delete
	gate (gate &&x) noexcept
gate &	operator= (gate &&x) noexcept
bool	try_enter () noexcept
void	enter ()
void	leave () noexcept
void	check ()
future	close () noexcept
size_t	get_count () const noexcept
	Returns a current number of registered in-progress requests.
bool	is_closed () const noexcept
	Returns whether the gate is closed.
holder	hold ()
std::optional< holder >	try_hold () noexcept

Related Functions
(Note that these are not member functions.)
template<typename Func >
auto	with_gate (gate &g, Func &&func)
template<typename Func >
auto	try_with_gate (gate &g, Func &&func) noexcept

Member Function Documentation

check()

void seastar::gate::check ( )

inline

Potentially stop an in-progress request.

If the gate is already closed, a gate_closed_exception is thrown. By using enter() and leave(), the program can ensure that no further requests are serviced. However, long-running requests may continue to run. The check() method allows such a long operation to voluntarily stop itself after the gate is closed, by making calls to check() in appropriate places. check() with throw an exception and bail out of the long-running code if the gate is closed.

Examples

closeable_test.cc.

close()

future seastar::gate::close ( )

inlinenoexcept

Closes the gate.

Future calls to enter() will fail with an exception, and when all current requests call leave(), the returned future will be made ready.

Examples

closeable_test.cc.

enter()

void seastar::gate::enter ( )

inline

Registers an in-progress request.

If the gate is not closed, the request is registered. Otherwise, a gate_closed_exception is thrown.

Examples

closeable_test.cc.

hold()

holder seastar::gate::hold ( )

inline

Get a RAII-based gate::holder object that enter()s the gate when constructed and leave()s it when destroyed.

Examples

closeable_test.cc.

leave()

void seastar::gate::leave ( )

inlinenoexcept

Unregisters an in-progress request.

If the gate is closed, and there are no more in-progress requests, the _stopped promise will be fulfilled.

Examples

closeable_test.cc.

try_enter()

bool seastar::gate::try_enter ( )

inlinenoexcept

Tries to register an in-progress request.

If the gate is not closed, the request is registered and the function returns true, Otherwise the function just returns false and has no other effect.

try_hold()

std::optional< holder > seastar::gate::try_hold ( )

inlinenoexcept

Try getting an optional RAII-based gate::holder object that enter()s the gate when constructed and leave()s it when destroyed. Returns std::nullopt iff the gate is closed.

Examples

closeable_test.cc.

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

• seastar/core/gate.hh