Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.


Provides signal functionality.

class signal_set




The type of the executor associated with the object.

Member Functions




Add a signal to a signal_set.


Start an asynchronous operation to wait for a signal to be delivered.


Cancel all operations associated with the signal set.


Remove all signals from a signal_set.


Get the executor associated with the object.


(Deprecated: Use get_executor().) Get the io_context associated with the object.


(Deprecated: Use get_executor().) Get the io_context associated with the object.


Remove a signal from a signal_set.


Construct a signal set without adding any signals.

Construct a signal set and add one signal.

Construct a signal set and add two signals.

Construct a signal set and add three signals.


Destroys the signal set.

The signal_set class provides the ability to perform an asynchronous wait for one or more signals to occur.

Thread Safety

Distinct objects: Safe.

Shared objects: Unsafe.


Performing an asynchronous wait:

void handler(
    const boost::system::error_code& error,
    int signal_number)
  if (!error)
    // A signal occurred.


// Construct a signal set registered for process termination.
boost::asio::signal_set signals(io_context, SIGINT, SIGTERM);

// Start an asynchronous wait for one of the signals to occur.
Queueing of signal notifications

If a signal is registered with a signal_set, and the signal occurs when there are no waiting handlers, then the signal notification is queued. The next async_wait operation on that signal_set will dequeue the notification. If multiple notifications are queued, subsequent async_wait operations dequeue them one at a time. Signal notifications are dequeued in order of ascending signal number.

If a signal number is removed from a signal_set (using the remove or erase member functions) then any queued notifications for that signal are discarded.

Multiple registration of signals

The same signal number may be registered with different signal_set objects. When the signal occurs, one handler is called for each signal_set object.

Note that multiple registration only works for signals that are registered using Asio. The application must not also register a signal handler using functions such as signal() or sigaction().

Signal masking on POSIX platforms

POSIX allows signals to be blocked using functions such as sigprocmask() and pthread_sigmask(). For signals to be delivered, programs must ensure that any signals registered using signal_set objects are unblocked in at least one thread.


Header: boost/asio/signal_set.hpp

Convenience header: boost/asio.hpp