An implementation of Logger that logs messages to an internal std::string buffer and provides read-only access to this buffer (for example, if one wants to write out its contents when exiting program). More...

#include <buffer_logger.hpp>

Inheritance diagram for flow::log::Buffer_logger:

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Public Member Functions
	Buffer_logger (Config *config)
	Constructs logger to subsequently log to a newly constructed internal `std::string` buffer. More...

bool	should_log (Sev sev, const Component &component) const override
	Implements interface method by returning `true` if the severity and component (which is allowed to be null) indicate it should. More...

bool	logs_asynchronously () const override
	Implements interface method by returning `false`, indicating that this Logger will not need the contents of `*metadata` and `msg` passed to do_log(), as the latter will output them synchronously. More...

void	do_log (Msg_metadata *metadata, util::String_view msg) override
	Implements interface method by synchronously logging the message and some subset of the metadata in a fashion controlled by m_config. More...

const std::string &	buffer_str () const
	Read-only access to the buffer string containing the messages logged thus far. More...

const std::string	buffer_str_copy () const
	Returns a copy of `buffer_str()` in thread-safe fashion. More...

Public Member Functions inherited from flow::log::Logger
virtual bool	should_log (Sev sev, const Component &component) const =0
	Given attributes of a hypothetical message that would be logged, return `true` if that message should be logged and `false` otherwise (e.g., if the verbosity of the message is above the current configured verbosity threshold for the Component specified). More...

virtual bool	logs_asynchronously () const =0
	Must return `true` if do_log() at least sometimes logs the given message and metadata (e.g., time stamp) after do_log() returns; `false` if this never occurs (i.e., it logs synchronously, always). More...

virtual void	do_log (Msg_metadata *metadata, util::String_view msg)=0
	Given a message and its severity, logs that message and possibly severity WITHOUT checking whether it should be logged (i.e., without performing logic that should_log() performs). More...

std::ostream *	this_thread_ostream () const
	Returns the stream dedicated to the executing thread and `this` Logger, so that the caller can apply state-setting formatters to it. More...

Public Member Functions inherited from flow::util::Null_interface
virtual	~Null_interface ()=0
	Boring `virtual` destructor. More...

Public Member Functions inherited from flow::util::Unique_id_holder
	Unique_id_holder ()
	Thread-safely construct an ID whose value is different from any other object of this class, past or future. More...

	Unique_id_holder (const Unique_id_holder &)
	This copy constructor is identical in behavior to Unique_id_holder(), the default ctor. More...

id_t	unique_id () const
	Raw unique ID identifying this object as well as any object of a derived type. More...

const Unique_id_holder &	operator= (const Unique_id_holder &) const
	This assignment operator is a `const` no-op. More...

Public Attributes
Config *const	m_config
	Reference to the config object passed to constructor. Note that object is mutable; see notes on thread safety. More...

Private Attributes
util::String_ostream	m_os
	Like `ostringstream` but allows for fast access directly into its internal string buffer. More...

Ostream_log_msg_writer	m_os_writer
	Wrapper around m_os that will take care of prefacing each message with time stamp, etc. More...

util::Mutex_non_recursive	m_log_mutex
	Mutex protecting against log messages being logged, accessing m_os concurrently and thus corrupting (or at best garbling) the output string `m_os.str()`. More...

Additional Inherited Members
Public Types inherited from flow::util::Unique_id_holder
using	id_t = uint64_t
	Raw integer type to uniquely identify a thing. 64-bit width should make overflow extremely hard to reach. More...

Static Public Member Functions inherited from flow::log::Logger
static void	this_thread_set_logged_nickname (util::String_view thread_nickname=util::String_view(), Logger *logger_ptr=0, bool also_set_os_name=true)
	Sets or unsets the current thread's logging-worthy string name; optionally sets the OS thread name (such as visible in `top` output). More...

static std::ostream &	this_thread_logged_name_os_manip (std::ostream &os)
	`ostream` manipulator function that, if output via `operator<<` to an `ostream`, will cause the current thread's logging-worthy string name to be output to that stream. More...

static void	set_thread_info_in_msg_metadata (Msg_metadata *msg_metadata)
	Loads `msg_metadata->m_call_thread_nickname` (if set) or else `msg_metadata->m_call_thread_id`, based on whether/how this_thread_set_logged_nickname() was last called in the current thread. More...

static void	set_thread_info (std::string call_thread_nickname, flow::util::Thread_id call_thread_id)
	Same as set_thread_info_in_msg_metadata() but targets the given two variables as opposed to a Msg_metadata. More...

Static Public Member Functions inherited from flow::util::Unique_id_holder
static id_t	create_unique_id ()
	Short-hand for `Unique_id_holder().unique_id()`; useful when all you want is the unique integer itself. More...

Detailed Description

An implementation of Logger that logs messages to an internal std::string buffer and provides read-only access to this buffer (for example, if one wants to write out its contents when exiting program).

Thread safety

Simultaneous logging from multiple threads is safe from output corruption, in that simultaneous do_log() calls for the same Logger will log serially to each other. buffer_str_copy() is also safe. However, buffer_str() may not be thread-safe; see its doc header for more information.

See thread safety notes and to-dos regarding m_config in Simple_ostream_logger doc header. These apply here also.

There are no other mutable data (state), so that's that.

Definition at line 44 of file buffer_logger.hpp.

Constructor & Destructor Documentation

◆ Buffer_logger()

flow::log::Buffer_logger::Buffer_logger ( Config * config )

explicit

Constructs logger to subsequently log to a newly constructed internal std::string buffer.

Parameters

config Controls behavior of this Logger. In particular, it affects should_log() logic (verbosity default and per-component) and output format (such as time stamp format). See thread safety notes in class doc header. This is saved in m_config.

Definition at line 27 of file buffer_logger.cpp.

Member Function Documentation

◆ buffer_str()

const std::string & flow::log::Buffer_logger::buffer_str ( ) const

Read-only access to the buffer string containing the messages logged thus far.

Warning: While high-performance, this is not thread-safe, in that other threads logging to *this may cause the returned string to be subsequently accessed mid-write and therefore possibly in an undefined state. Take care to access the result only when you know no other thread is logging (e.g., when exiting program).

Returns: Read-only reference.

Definition at line 53 of file buffer_logger.cpp.

References m_os, and flow::util::String_ostream::str().

Referenced by buffer_str_copy().

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◆ buffer_str_copy()

const std::string flow::log::Buffer_logger::buffer_str_copy ( ) const

Returns a copy of buffer_str() in thread-safe fashion.

However, this may be quite slow if done frequently.

Returns: Newly created string.

Definition at line 58 of file buffer_logger.cpp.

References buffer_str(), and m_log_mutex.

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◆ do_log()

void flow::log::Buffer_logger::do_log	(	Msg_metadata *	metadata,
		util::String_view	msg
	)

overridevirtual

Implements interface method by synchronously logging the message and some subset of the metadata in a fashion controlled by m_config.

Internally, this will involve a possible allocation (to enlarge an internal buffer when needed) and essentially copying of the msg and *metadata payloads onto the end of the buffer. This does not block (in the classic I/O sense) the calling thread. Needless to say, memory use may become a concern depending on the verbosity of the logging.

Parameters

metadata	All information to potentially log in addition to `msg`.
msg	The message.

Implements flow::log::Logger.

Definition at line 44 of file buffer_logger.cpp.

References flow::log::Ostream_log_msg_writer::log(), m_log_mutex, and m_os_writer.

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◆ logs_asynchronously()

bool flow::log::Buffer_logger::logs_asynchronously ( ) const

overridevirtual

Implements interface method by returning false, indicating that this Logger will not need the contents of *metadata and msg passed to do_log(), as the latter will output them synchronously.

Returns: See above.

Implements flow::log::Logger.

Definition at line 39 of file buffer_logger.cpp.

◆ should_log()

bool flow::log::Buffer_logger::should_log	(	Sev	sev,
		const Component &	component
	)		const

overridevirtual

Implements interface method by returning true if the severity and component (which is allowed to be null) indicate it should.

As of this writing not thread-safe against changes to *m_config.

Parameters

sev	Severity of the message.
component	Component of the message. Reminder: `component.empty() == true` is allowed.

Returns: See above.

Implements flow::log::Logger.

Definition at line 34 of file buffer_logger.cpp.

Member Data Documentation

◆ m_config

Config* const flow::log::Buffer_logger::m_config

Reference to the config object passed to constructor. Note that object is mutable; see notes on thread safety.

Definition at line 120 of file buffer_logger.hpp.

◆ m_log_mutex

util::Mutex_non_recursive flow::log::Buffer_logger::m_log_mutex

mutableprivate

Mutex protecting against log messages being logged, accessing m_os concurrently and thus corrupting (or at best garbling) the output string m_os.str().

Definition at line 135 of file buffer_logger.hpp.

Referenced by buffer_str_copy(), and do_log().

◆ m_os

util::String_ostream flow::log::Buffer_logger::m_os

private

Like ostringstream but allows for fast access directly into its internal string buffer.

Definition at line 126 of file buffer_logger.hpp.

Referenced by buffer_str().

◆ m_os_writer

Ostream_log_msg_writer flow::log::Buffer_logger::m_os_writer

private

Wrapper around m_os that will take care of prefacing each message with time stamp, etc.

Definition at line 129 of file buffer_logger.hpp.

Referenced by do_log().

The documentation for this class was generated from the following files:

log/buffer_logger.hpp
log/buffer_logger.cpp

Public Member Functions

Public Attributes

Private Attributes

Additional Inherited Members

Detailed Description

Thread safety

Constructor & Destructor Documentation

◆ Buffer_logger()

Member Function Documentation

◆ buffer_str()

◆ buffer_str_copy()

◆ do_log()

◆ logs_asynchronously()

◆ should_log()

Member Data Documentation

◆ m_config

◆ m_log_mutex

◆ m_os

◆ m_os_writer