log.cpp File Reference

Implementation of the logging facility. More...

#include "cppthread/log.h"
#include "cppthread/exception.h"
#include <cstring>
#include <iostream>
#include <snapdev/poison.h>

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Functions
void	cppthread::create_system_mutex ()
	Function used to initialize the system mutex.
void	cppthread::set_log_callback (log_callback callback)
	Set a callback function.
std::string	cppthread::to_string (log_level_t level)
	Convert a log level to a string.

Variables
logger	cppthread::log
	The logger object used to send logs out.

Detailed Description

The library is very often used by daemons meaning that it will be running on its own in the background. For this reason, all the output is done through the log facility.

This interface defines a function which you are expected to call to setup a callback. By default, the callback is set to a function that simply prints errors to std::cerr.

Note

Note that the log facility is used only in extreme cases. It was made fully thread safe, however, that implementation is considered slow. Especially, if two different threads attempt to log a message simultaneously, only one of them will be allowed to build their message and the other one will be blocked for the entire time. Our snaplogger, on the other hand, allows any number of threads to generate errors in parallel, only the processing at the end, which can be done asynchronously, requires serialization.

Definition in file log.cpp.

Function Documentation

create_system_mutex()

void cppthread::create_system_mutex ( )

extern

This is an internal function called by the logger constructor.

This is unfortunate, but the system mutex create relies on the log object to exist and be properly initialized before it gets created. So we call this function from the constructor of the logger.

Note

This means it's not exact properly initialized since the constructor did not yet return. However, it is guaranteed to work properly since we do not allow derivations or virtual tables.

The logger constructor is called whenever the cppthread library is loaded and that happens in your main thread at initialization time. This means any of your code can access the g_system_mutex as required.

This function is not defined externally so that other users can't call it from the outside (there would be no need anyway). Just in case, if called a second time, the function writes an error message and fails with a call to std::terminate().

Another way to safely create a new mutex is to use a static variable in a function. The initialization of that static variable will always be safe so that mutex will be available to all your threads even if you already had multiple threads the first time that function was called.

void myfunc()
{
    static cppthread::mutex m = cppthread::mutex();
 
    // here "m" is a safe to use mutex
    cppthread::guard lock(m);
 
    ...do atomic work here...
}

You could even create a function which returns a reference to that local mutex (just make sure you don't copy that mutex).

Note

Although this function gets called from the logger contructor, it is not used by the logger at all.

Definition at line 926 of file mutex.cpp.

References cppthread::create_system_mutex(), and cppthread::g_system_mutex.

Referenced by cppthread::logger::logger(), and cppthread::create_system_mutex().

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set_log_callback()

void cppthread::set_log_callback

(

log_callback

callback

)

Set a callback function used to redirect the logs generated by the cppthread library and any library that makes use of this log facility (i.e. the advgetopt project does so).

Note

You should not use this facility unless you do not have access to the snaplogger, somehow. The snaplogger is a much more advanced and better interface especially in a multithreaded application.

Parameters

[in]

callback

The function to call whenever a log is generated.

Definition at line 170 of file log.cpp.

References cppthread::set_log_callback().

Referenced by cppthread::set_log_callback().

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to_string()

std::string cppthread::to_string

(

log_level_t

level

)

This function transforms a log_level_t value to a string which can then be used in a log message.

Exceptions

cppthread_invalid_error

If the log level is not one of the know log levels, then the function raises this exception.

Parameters

[in]

level

The message log level to convert to a string.

Returns

A string representing the log level.

Definition at line 610 of file log.cpp.

References cppthread::to_string().

Referenced by cppthread::pool< W, A >::worker_thread_t::worker_thread_t(), cppthread::logger::end(), and cppthread::to_string().

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Variable Documentation

log

logger cppthread::log

This object is used to send data to the logger.

Note

This works because this library does not create a thread on initialization and therefore there is no reason for this library to initiate a logger call. At least, at this time, this is true and I'm not too sure what could generate such a problem.

Definition at line 90 of file log.cpp.

Referenced by cppthread::mutex::mutex(), cppthread::guard::~guard(), cppthread::mutex::~mutex(), cppthread::runner::~runner(), cppthread::thread::~thread(), cppthread::mutex::broadcast(), cppthread::mutex::dated_wait(), cppthread::runner::enter(), cppthread::thread::init(), cppthread::thread::internal_enter(), cppthread::thread::internal_leave(), cppthread::thread::internal_run(), cppthread::thread::internal_thread(), cppthread::runner::leave(), cppthread::mutex::lock(), cppthread::mutex::safe_broadcast(), cppthread::mutex::safe_signal(), cppthread::mutex::signal(), cppthread::thread::start(), cppthread::mutex::timed_wait(), cppthread::mutex::try_lock(), cppthread::mutex::unlock(), and cppthread::mutex::wait().