221 lines
8.3 KiB
Plaintext
221 lines
8.3 KiB
Plaintext
[/
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/ Copyright (c) 2003-2019 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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/
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/ Distributed under the Boost Software License, Version 1.0. (See accompanying
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/ file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:handler_tracking Handler Tracking]
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To aid in debugging asynchronous programs, Boost.Asio provides support for handler
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tracking. When enabled by defining `BOOST_ASIO_ENABLE_HANDLER_TRACKING`, Boost.Asio
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writes debugging output to the standard error stream. The output records
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asynchronous operations and the relationships between their handlers.
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[teletype]
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This feature is useful when debugging and you need to know how your
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asynchronous operations are chained together, or what the pending asynchronous
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operations are. As an illustration, here is the output when you run the HTTP
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Server example, handle a single request, then shut down via Ctrl+C:
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@asio|1512254357.979980|0*1|signal_set@0x7ffeaaaa20d8.async_wait
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@asio|1512254357.980127|0*2|socket@0x7ffeaaaa20f8.async_accept
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@asio|1512254357.980150|.2|non_blocking_accept,ec=asio.system:11
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@asio|1512254357.980162|0|resolver@0x7ffeaaaa1fd8.cancel
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@asio|1512254368.457147|.2|non_blocking_accept,ec=system:0
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@asio|1512254368.457193|>2|ec=system:0
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@asio|1512254368.457219|2*3|socket@0x55cf39f0a238.async_receive
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@asio|1512254368.457244|.3|non_blocking_recv,ec=system:0,bytes_transferred=141
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@asio|1512254368.457275|2*4|socket@0x7ffeaaaa20f8.async_accept
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@asio|1512254368.457293|.4|non_blocking_accept,ec=asio.system:11
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@asio|1512254368.457301|<2|
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@asio|1512254368.457310|>3|ec=system:0,bytes_transferred=141
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@asio|1512254368.457441|3*5|socket@0x55cf39f0a238.async_send
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@asio|1512254368.457502|.5|non_blocking_send,ec=system:0,bytes_transferred=156
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@asio|1512254368.457511|<3|
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@asio|1512254368.457519|>5|ec=system:0,bytes_transferred=156
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@asio|1512254368.457544|5|socket@0x55cf39f0a238.close
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@asio|1512254368.457559|<5|
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@asio|1512254371.385106|>1|ec=system:0,signal_number=2
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@asio|1512254371.385130|1|socket@0x7ffeaaaa20f8.close
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@asio|1512254371.385163|<1|
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@asio|1512254371.385175|>4|ec=asio.system:125
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@asio|1512254371.385182|<4|
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@asio|1512254371.385202|0|signal_set@0x7ffeaaaa20d8.cancel
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Each line is of the form:
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<tag>|<timestamp>|<action>|<description>
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The `<tag>` is always `@asio`, and is used to identify and extract the handler
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tracking messages from the program output.
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The `<timestamp>` is seconds and microseconds from 1 Jan 1970 UTC.
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The `<action>` takes one of the following forms:
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[variablelist
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[
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[>n]
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[The program entered the handler number `n`. The `<description>` shows the
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arguments to the handler.]
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]
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[
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[<n]
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[The program left handler number `n`.]
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]
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[
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[!n]
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[The program left handler number n due to an exception.]
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]
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[
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[~n]
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[The handler number `n` was destroyed without having been invoked. This is
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usually the case for any unfinished asynchronous operations when the
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`io_context` is destroyed.]
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]
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[
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[n*m]
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[The handler number `n` created a new asynchronous operation with completion
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handler number `m`. The `<description>` shows what asynchronous operation
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was started.]
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]
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[
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[n]
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[The handler number `n` performed some other operation. The `<description>`
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shows what function was called. Currently only `close()` and `cancel()`
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operations are logged, as these may affect the state of pending
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asynchronous operations.]
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]
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[
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[.n]
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[The implementation performed a system call as part of the asynchronous
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operation for which handler number `n` is the completion handler. The
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`<description>` shows what function was called and its results. These
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tracking events are only emitted when using a reactor-based
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implementation.]
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]
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]
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Where the `<description>` shows a synchronous or asynchronous operation, the
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format is `<object-type>@<pointer>.<operation>`. For handler entry, it shows a
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comma-separated list of arguments and their values.
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As shown above, Each handler is assigned a numeric identifier. Where the
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handler tracking output shows a handler number of 0, it means that the action
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was performed outside of any handler.
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[heading Visual Representations]
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The handler tracking output may be post-processed using the included
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[^handlerviz.pl] tool to create a visual representation of the handlers
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(requires the GraphViz tool [^dot]).
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[c++]
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[heading Custom Tracking]
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Handling tracking may be customised by defining the
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`BOOST_ASIO_CUSTOM_HANDLER_TRACKING` macro to the name of a header file
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(enclosed in `""` or `<>`). This header file must implement the following
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preprocessor macros:
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[table
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[[Macro] [Description]]
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[
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[`BOOST_ASIO_INHERIT_TRACKED_HANDLER`]
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[Specifies a base class for classes that implement asynchronous operations.
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When used, the macro immediately follows the class name, so it must have
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the form `: public my_class`.]
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]
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[
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[`BOOST_ASIO_ALSO_INHERIT_TRACKED_HANDLER`]
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[Specifies a base class for classes that implement asynchronous operations.
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When used, the macro follows other base classes, so it must have the form
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`, public my_class`.]
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]
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[
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[`BOOST_ASIO_HANDLER_TRACKING_INIT(args)`]
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[An expression that is used to initialise the tracking mechanism.]
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]
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[
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[`BOOST_ASIO_HANDLER_CREATION(args)`]
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[An expression that is called on creation of an asynchronous operation.
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`args` is a parenthesised function argument list containing the owning
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execution context, the tracked handler, the name of the object type, a
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pointer to the object, the object's native handle, and the operation name.]
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]
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[
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[`BOOST_ASIO_HANDLER_COMPLETION(args)`]
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[An expression that is called on completion of an asynchronous operation.
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`args` is a parenthesised function argument list containing the tracked
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handler.]
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]
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[
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[`BOOST_ASIO_HANDLER_INVOCATION_BEGIN(args)`]
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[An expression that is called immediately before a completion handler is
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invoked. `args` is a parenthesised function argument list containing the
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arguments to the completion handler.]
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]
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[
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[`BOOST_ASIO_HANDLER_INVOCATION_END`]
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[An expression that is called immediately after a completion handler is
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invoked.]
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]
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[
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[`BOOST_ASIO_HANDLER_OPERATION(args)`]
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[An expression that is called when some synchronous object operation is
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called (such as `close()` or `cancel()`). `args` is a parenthesised
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function argument list containing the owning execution context, the name
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of the object type, a pointer to the object, the object's native handle,
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and the operation name.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_REGISTRATION(args)`]
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[An expression that is called when an object is registered with the
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reactor. `args` is a parenthesised function argument list containing the
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owning execution context, the object's native handle, and a unique
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registration key.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_DEREGISTRATION(args)`]
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[An expression that is called when an object is deregistered from the
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reactor. `args` is a parenthesised function argument list containing the
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owning execution context, the object's native handle, and a unique
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registration key.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_READ_EVENT`]
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[A bitmask constant used to identify reactor read readiness events.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_WRITE_EVENT`]
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[A bitmask constant used to identify reactor write readiness events.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_ERROR_EVENT`]
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[A bitmask constant used to identify reactor error readiness events.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_EVENTS(args)`]
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[An expression that is called when an object registered with the reactor
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becomes ready. `args` is a parenthesised function argument list containing
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the owning execution context, the unique registration key, and a bitmask of
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the ready events.]
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]
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[
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[`BOOST_ASIO_HANDLER_REACTOR_OPERATION(args)`]
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[An expression that is called when the implementation performs a system
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call as part of a reactor-based asynchronous operation. `args` is a
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parenthesised function argument list containing the tracked handler, the
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operation name, the error code produced by the operation, and (optionally)
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the number of bytes transferred.]
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]
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]
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[heading See Also]
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[link boost_asio.examples.cpp11_examples.handler_tracking Custom handler tracking
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example].
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[endsect]
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