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## Class shared_connection_block

boost::signals2::shared_connection_block — Blocks a connection between a signal and a slot.

## Synopsis

    // In header: <boost/signals2/shared_connection_block.hpp>

    class shared_connection_block {
    public:
      // construct/copy/destruct
      shared_connection_block(const boost::signals2::connection & = connection(),
                              bool = true);
      shared_connection_block(const boost::signals2::shared_connection_block &);
      shared_connection_block&
      operator=(const boost::signals2::shared_connection_block &);
      ~shared_connection_block();

      // connection blocking
      void unblock();
      void block();
      bool blocking() const;

      // miscellaneous methods
      boost::signals2::connection connection() const;
    };

## Description

A `shared_connection_block` object blocks a connection, preventing the associated slot from executing when the associated signal is invoked. The connection will remain blocked until every `shared_connection_block` that references the connection releases its block. A `shared_connection_block` releases its block when it is destroyed or its unblock method is called.

A `shared_connection_block` is safe to use even after the signals2::connection object it was constructed from has been destroyed, or the connection it references has been disconnected.

Note, blocking a connection does not guarantee the associated slot has finished execution if it is already in the process of being run when the connection block goes into effect. This is similar to the behaviour of disconnect, in that blocking a connection will not wait for the connection's associated slot to complete execution. This situation may arise in a multi-threaded environment if the connection block goes into effect concurrently with signal invocation, or in a single-threaded environment if a slot blocks its own connection.

### `shared_connection_block` public construct/copy/destruct

1.     shared_connection_block(const boost::signals2::connection & conn = connection(),
                               bool initially_blocking = true);

   Effects: | Creates a `shared_connection_block` which can block the connection referenced by `conn`. The `shared_connection_block` will initially block the connection if and only if the `initially_blocking` parameter is `true`. The block on the connection may be released by calling the unblock method, or destroying the `shared_connection_block` object. Default construction of a `shared_connection_block` results in a `shared_connection_block` which references the NULL connection. Such a `shared_connection_block` is safe to use, though not particularly useful until it is assigned another `shared_connection_block` which references a real connection.
   Postconditions: | `this->blocking() == initially_blocking`

2.     shared_connection_block(const boost::signals2::shared_connection_block & other);

   Effects: | Copy constructs a `shared_connection_block` which references the same connection as `other`.
   Postconditions: | `this->connection() == other.connection()` `this->blocking() == other.blocking()`

3.     shared_connection_block&
       operator=(const boost::signals2::shared_connection_block & rhs);

   Effects: | Makes `this` reference the same connection as `rhs`.
   Postconditions: | `this->connection() == rhs.connection()` `this->blocking() == rhs.blocking()`
   Throws: | Will not throw.

4.     ~shared_connection_block();

   Effects: | If blocking() is true, releases the connection block.

### `shared_connection_block` connection blocking

1.     void unblock();

   Effects: | If blocking() is true, releases the connection block. Note, the connection may remain blocked due to other `shared_connection_block` objects.
   Postconditions: | `this->blocking() == false`.

2.     void block();

   Effects: | If blocking() is false, reasserts a block on the connection.
   Postconditions: | `this->blocking() == true`.

3.     bool blocking() const;

   Returns: | `true` if `this` is asserting a block on the connection.
   Notes: | `this->blocking() == true` implies `connection::blocked() == true` for the connection. However, `this->blocking() == false` does not necessarily imply `connection::blocked() == false`, since the connection may be blocked by another `shared_connection_block` object.

### `shared_connection_block` miscellaneous methods

1.     boost::signals2::connection connection() const;

   Returns: | A connection object for the connection referenced by `this`.