...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Typedef for a timer based on the system clock.
typedef basic_waitable_timer< chrono::system_clock > system_timer;
Name |
Description |
---|---|
The clock type. |
|
The duration type of the clock. |
|
The underlying implementation type of I/O object. |
|
The type of the service that will be used to provide I/O operations. |
|
The time point type of the clock. |
|
The wait traits type. |
Name |
Description |
---|---|
Start an asynchronous wait on the timer. |
|
Constructor. Constructor to set a particular expiry time as an absolute time. Constructor to set a particular expiry time relative to now. |
|
Cancel any asynchronous operations that are waiting on the timer. |
|
Cancels one asynchronous operation that is waiting on the timer. |
|
Get the timer's expiry time as an absolute time. Set the timer's expiry time as an absolute time. |
|
Get the timer's expiry time relative to now. Set the timer's expiry time relative to now. |
|
Get the io_service associated with the object. |
|
Perform a blocking wait on the timer. |
Name |
Description |
---|---|
Get the underlying implementation of the I/O object. |
|
Get the service associated with the I/O object. |
Name |
Description |
---|---|
(Deprecated: Use get_implementation().) The underlying implementation of the I/O object. |
|
(Deprecated: Use get_service().) The service associated with the I/O object. |
The basic_waitable_timer
class template
provides the ability to perform a blocking or asynchronous wait for a timer
to expire.
A waitable timer is always in one of two states: "expired" or "not
expired". If the wait()
or async_wait()
function is called on an expired timer,
the wait operation will complete immediately.
Most applications will use one of the steady_timer
, system_timer
or high_resolution_timer
typedefs.
This waitable timer functionality is for use with the C++11 standard library's
<chrono>
facility, or with the Boost.Chrono library.
Distinct objects: Safe.
Shared objects: Unsafe.
Performing a blocking wait (C++11):
// Construct a timer without setting an expiry time. boost::asio::steady_timer timer(io_service); // Set an expiry time relative to now. timer.expires_from_now(std::chrono::seconds(5)); // Wait for the timer to expire. timer.wait();
Performing an asynchronous wait (C++11):
void handler(const boost::system::error_code& error) { if (!error) { // Timer expired. } } ... // Construct a timer with an absolute expiry time. boost::asio::steady_timer timer(io_service, std::chrono::steady_clock::now() + std::chrono::seconds(60)); // Start an asynchronous wait. timer.async_wait(handler);
Changing the expiry time of a timer while there are pending asynchronous waits causes those wait operations to be cancelled. To ensure that the action associated with the timer is performed only once, use something like this: used:
void on_some_event() { if (my_timer.expires_from_now(seconds(5)) > 0) { // We managed to cancel the timer. Start new asynchronous wait. my_timer.async_wait(on_timeout); } else { // Too late, timer has already expired! } } void on_timeout(const boost::system::error_code& e) { if (e != boost::asio::error::operation_aborted) { // Timer was not cancelled, take necessary action. } }
boost::asio::basic_waitable_timer::expires_from_now()
function cancels any pending asynchronous waits, and returns the number
of asynchronous waits that were cancelled. If it returns 0 then you were
too late and the wait handler has already been executed, or will soon
be executed. If it returns 1 then the wait handler was successfully cancelled.
boost::asio::error::operation_aborted
.
This typedef uses the C++11 <chrono>
standard library facility, if available. Otherwise, it may use the Boost.Chrono
library. To explicitly utilise Boost.Chrono, use the basic_waitable_timer
template directly:
typedef basic_waitable_timer<boost::chrono::system_clock> timer;
Header: boost/asio/system_timer.hpp
Convenience header: None