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## Revision History

#### Asio 1.4.6 / Boost 1.44

- Reduced compile times. (Note that some programs may need to add additional `#include`s, e.g. if the program uses `boost::array` but does not explicitly include `<boost/array.hpp>`.)
- Reduced the size of generated code.
- Refactored `deadline_timer` implementation to improve performance.
- Improved multiprocessor scalability on Windows by using a dedicated hidden thread to wait for timers.
- Improved performance of `asio::streambuf` with `async_read()` and `async_read_until()`. These read operations now use the existing capacity of the `streambuf` when reading, rather than limiting the read to 512 bytes.
- Added optional separate compilation. To enable, add `#include <boost/asio/impl/src.cpp>` to one source file in a program, then build the program with `BOOST_ASIO_SEPARATE_COMPILATION` defined in the project/compiler settings. Alternatively, `BOOST_ASIO_DYN_LINK` may be defined to build a separately-compiled Asio as part of a shared library.
- Added new macro `BOOST_ASIO_DISABLE_FENCED_BLOCK` to permit the disabling of memory fences around completion handlers, even if thread support is enabled.
- Reworked timeout examples to better illustrate typical use cases.
- Ensured that handler arguments are passed as `const` types.
- Fixed incorrect parameter order in `null_buffers` variant of `async_send_to` (#4170).
- Ensured `unsigned char` is used with `isdigit` in `getaddrinfo` emulation (#4201).
- Fixed handling of very small but non-zero timeouts (#4205).
- Fixed crash that occurred when an empty buffer sequence was passed to a composed read or write operation.
- Added missing `operator+` overload in `buffers_iterator` (#4382).
- Implemented cancellation of `null_buffers` operations on Windows.

#### Asio 1.4.5 / Boost 1.43

- Improved performance.
- Reduced compile times.
- Reduced the size of generated code.
- Extended the guarantee that background threads don't call user code to all asynchronous operations (#3923).
- Changed to use edge-triggered epoll on Linux.
- Changed to use `timerfd` for dispatching timers on Linux, when available.
- Changed to use one-shot notifications with kqueue on Mac OS X and BSD platforms.
- Added a bitmask type `ip::resolver_query_base::flags` as per the TR2 proposal. This type prevents implicit conversion from `int` to `flags`, allowing the compiler to catch cases where users incorrectly pass a numeric port number as the service name.
- Added `#define NOMINMAX` for all Windows compilers. Users can define `BOOST_ASIO_NO_NOMINMAX` to suppress this definition (#3901).
- Fixed a bug where 0-byte asynchronous reads were incorrectly passing an `error::eof` result to the completion handler (#4023).
- Changed the `io_control()` member functions to always call `ioctl` on the underlying descriptor when modifying blocking mode (#3307).
- Changed the resolver implementation to longer require the typedefs `InternetProtocol::resolver_query` and `InternetProtocol::resolver_iterator`, as neither typedef is part of the documented `InternetProtocol` requirements. The corresponding typedefs in the `ip::tcp`, `ip::udp` and `ip::icmp` classes have been deprecated.
- Fixed out-of-band handling for reactors not based on `select()`.
- Added new `BOOST_ASIO_DISABLE_THREADS` macro that allows Asio's threading support to be independently disabled.
- Minor documentation improvements.

#### Asio 1.4.4 / Boost 1.42

- Added a new HTTP Server 4 example illustrating the use of stackless coroutines with Asio.
- Changed handler allocation and invocation to use `boost::addressof` to get the address of handler objects, rather than applying `operator&` directly (#2977).
- Restricted MSVC buffer debugging workaround to 2008, as it causes a crash with 2010 beta 2 (#3796, #3822).
- Fixed a problem with the lifetime of handler memory, where Windows needs the `OVERLAPPED` structure to be valid until both the initiating function call has returned and the completion packet has been delivered.
- Don't block signals while performing system calls, but instead restart the calls if they are interrupted.
- Documented the guarantee made by strand objects with respect to order of handler invocation.
- Changed strands to use a pool of implementations, to make copying of strands cheaper.
- Ensured that kqueue support is enabled for BSD platforms (#3626).
- Added a `boost_` prefix to the `extern "C"` thread entry point function (#3809).
- In `getaddrinfo` emulation, only check the socket type (`SOCK_STREAM` or `SOCK_DGRAM`) if a service name has been specified. This should allow the emulation to work with raw sockets.
- Added a workaround for some broken Windows firewalls that make a socket appear bound to 0.0.0.0 when it is in fact bound to 127.0.0.1.
- Applied a fix for reported excessive CPU usage under Solaris (#3670).
- Added some support for platforms that use older compilers such as g++ 2.95 (#3743).

#### Asio 1.4.3 / Boost 1.40

- Added a new ping example to illustrate the use of ICMP sockets.
- Changed the `buffered*_stream<>` templates to treat 0-byte reads and writes as no-ops, to comply with the documented type requirements for `SyncReadStream`, `AsyncReadStream`, `SyncWriteStream` and `AsyncWriteStream`.
- Changed some instances of the `throw` keyword to `boost::throw_exception()` to allow Asio to be used when exception support is disabled. Note that the SSL wrappers still require exception support (#2754).
- Made Asio compatible with the OpenSSL 1.0 beta (#3256).
- Eliminated a redundant system call in the Solaris `/dev/poll` backend.
- Fixed a bug in resizing of the bucket array in the internal hash maps (#3095).
- Ensured correct propagation of the error code when a synchronous accept fails (#3216).
- Ensured correct propagation of the error code when a synchronous read or write on a Windows HANDLE fails.
- Fixed failures reported when `_GLIBCXX_DEBUG` is defined (#3098).
- Fixed custom memory allocation support for timers (#3107).
- Tidied up various warnings reported by g++ (#1341, #2618).
- Various documentation improvements, including more obvious hyperlinks to function overloads, header file information, examples for the handler type requirements, and adding enum values to the index (#3157, #2620).

#### Asio 1.4.2 / Boost 1.39

- Implement automatic resizing of the bucket array in the internal hash maps. This is to improve performance for very large numbers of asynchronous operations and also to reduce memory usage for very small numbers. A new macro `BOOST_ASIO_HASH_MAP_BUCKETS` may be used to tweak the sizes used for the bucket arrays. (N.B. this feature introduced a bug which was fixed in Asio 1.4.3 / Boost 1.40.)
- Add performance optimisation for the Windows IOCP backend for when no timers are used.
- Prevent locale settings from affecting formatting of TCP and UDP endpoints (#2682).
- Fix a memory leak that occurred when an asynchronous SSL operation's completion handler threw an exception (#2910).
- Fix the implementation of `io_control()` so that it adheres to the documented type requirements for IoControlCommand (#2820).
- Fix incompatibility between Asio and ncurses.h (#2156).
- On Windows, specifically handle the case when an overlapped `ReadFile` call fails with `ERROR_MORE_DATA`. This enables a hack where a `windows::stream_handle` can be used with a message-oriented named pipe (#2936).
- Fix system call wrappers to always clear the error on success, as POSIX allows successful system calls to modify errno (#2953).
- Don't include termios.h if `BOOST_ASIO_DISABLE_SERIAL_PORT` is defined (#2917).
- Cleaned up some more MSVC level 4 warnings (#2828).
- Various documentation fixes (#2871).

#### Asio 1.4.1 / Boost 1.38

- Improved compatibility with some Windows firewall software.
- Ensured arguments to `windows::overlapped_ptr::complete()` are correctly passed to the completion handler (#2614).
- Fixed a link problem and multicast failure on QNX (#2504, #2530).
- Fixed a compile error in SSL support on MinGW / g++ 3.4.5.
- Drop back to using a pipe for notification if eventfd is not available at runtime on Linux (#2683).
- Various minor bug and documentation fixes (#2534, #2541, #2607, #2617, #2619).

#### Asio 1.4.0 / Boost 1.37

- Enhanced CompletionCondition concept with the signature `size_t CompletionCondition(error_code ec, size_t total)`, where the return value indicates the maximum number of bytes to be transferred on the next read or write operation. (The old CompletionCondition signature is still supported for backwards compatibility).
- New windows::overlapped_ptr class to allow arbitrary overlapped I/O functions (such as TransmitFile) to be used with Asio.
- On recent versions of Linux, an eventfd descriptor is now used (rather than a pipe) to interrupt a blocked select/epoll reactor.
- Added const overloads of lowest_layer().
- Synchronous read, write, accept and connect operations are now thread safe (meaning that it is now permitted to perform concurrent synchronous operations on an individual socket, if supported by the OS).
- Reactor-based io_service implementations now use lazy initialisation to reduce the memory usage of an io_service object used only as a message queue.

#### Asio 1.2.0 / Boost 1.36

- Added support for serial ports.
- Added support for UNIX domain sockets.
- Added support for raw sockets and ICMP.
- Added wrappers for POSIX stream-oriented file descriptors (excluding regular files).
- Added wrappers for Windows stream-oriented `HANDLE`s such as named pipes (requires `HANDLE`s that work with I/O completion ports).
- Added wrappers for Windows random-access `HANDLE`s such as files (requires `HANDLE`s that work with I/O completion ports).
- Added support for reactor-style operations (i.e. they report readiness but perform no I/O) using a new `null_buffers` type.
- Added an iterator type for bytewise traversal of buffer sequences.
- Added new `read_until()` and `async_read_until()` overloads that take a user-defined function object for locating message boundaries.
- Added an experimental two-lock queue (enabled by defining `BOOST_ASIO_ENABLE_TWO_LOCK_QUEUE`) that may provide better `io_service` scalability across many processors.
- Various fixes, performance improvements, and more complete coverage of the custom memory allocation support.

#### Asio 1.0.0 / Boost 1.35

First release of Asio as part of Boost.