Base class of all monitors. More...

#include <monitor.hpp>

Inheritance diagram for fsw::monitor:

Public Member Functions
	monitor (std::vector< std::string > paths, FSW_EVENT_CALLBACK callback, void context=nullptr)
	Constructs a monitor watching the specified `paths`. More...

virtual	~monitor ()
	Destructs a monitor instance. More...

	monitor (const monitor &orig)=delete
	This class is not copy constructible.

monitor &	operator= (const monitor &that)=delete
	This class is not copy assignable.

void	set_property (const std::string &name, const std::string &value)
	Sets a custom property. More...

void	set_properties (const std::map< std::string, std::string > options)
	Sets the custom properties. More...

std::string	get_property (std::string name)
	Gets the value of a property. More...

void	set_latency (double latency)
	Sets the latency. More...

void	set_fire_idle_event (bool fire_idle_event)
	Sets the fire idle event flag. More...

void	set_allow_overflow (bool overflow)
	Notify buffer overflows as change events. More...

void	set_recursive (bool recursive)
	Recursively scan subdirectories. More...

void	set_directory_only (bool directory_only)
	Watch directories only. More...

void	add_filter (const monitor_filter &filter)
	Add a path filter. More...

void	set_filters (const std::vector< monitor_filter > &filters)
	Set the path filters. More...

void	set_follow_symlinks (bool follow)
	Follow symlinks. More...

void *	get_context () const
	Get the pointer to the context data. More...

void	set_context (void *context)
	Set the context data. More...

void	start ()
	Start the monitor. More...

void	stop ()
	Stop the monitor. More...

bool	is_running ()
	Check whether the monitor is running. More...

void	add_event_type_filter (const fsw_event_type_filter &filter)
	Add an event type filter. More...

void	set_event_type_filters (const std::vector< fsw_event_type_filter > &filters)
	Set the event type filters. More...

void	set_watch_access (bool access)
	Monitor file access. More...

Protected Member Functions
bool	accept_event_type (fsw_event_flag event_type) const
	Check whether an event should be accepted. More...

bool	accept_path (const std::string &path) const
	Check whether a path should be accepted. More...

bool	accept_path (const char *path) const
	Check whether a path should be accepted. More...

void	notify_events (const std::vector< event > &events) const
	Notify change events. More...

void	notify_overflow (const std::string &path) const
	Notify an overflow event. More...

std::vector< fsw_event_flag >	filter_flags (const event &evt) const
	Filter event types. More...

virtual void	run ()=0
	Execute monitor loop. More...

virtual void	on_stop ()
	Execute an implementation-specific stop handler. More...

Protected Attributes
std::vector< std::string >	paths
	List of paths to watch. More...

std::map< std::string, std::string >	properties
	Map of custom properties. More...

FSW_EVENT_CALLBACK *	callback
	Callback to which change events should be notified. More...

void *	context = nullptr
	Pointer to context data that will be passed to the monitor::callback.

double	latency = 1.0
	Latency of the monitor.

bool	fire_idle_event = false
	If `true`, the monitor will notify an event when idle. More...

bool	allow_overflow = false
	If `true`, queue overflow events will be notified to the caller, otherwise the monitor will throw a libfsw_exception.

bool	recursive = false
	If `true`, directories will be scanned recursively.

bool	follow_symlinks = false
	If `true`, symbolic links are followed.

bool	directory_only = false
	Flag indicating whether only directories should be monitored.

bool	watch_access = false
	Flag indicating whether file access should be watched.

bool	running = false
	Flag indicating whether the monitor is in the running state.

bool	should_stop = false
	Flag indicating whether the monitor should preemptively stop.

std::mutex	run_mutex
	Mutex used to serialize access to the monitor state from multiple threads.

std::mutex	notify_mutex
	Mutex used to serialize access to the notify_events() method.

Detailed Description

Base class of all monitors.

The fsw::monitor class is the base class of all monitors. This class encapsulates the common functionality of a monitor:

Accessors to configuration parameters.
start() and stop() lifecycle.
Event filtering.
Event notification to user-provided callback function.

Since some methods are designed to be called from different threads, this class provides an internal mutex (monitor::run_mutex) that implementors should lock on when accessing shared state. The mutex is available only when HAVE_CXX_MUTEX is defined.

At least the following tasks must be performed to implement a monitor:

Providing an implementation of the run() method.
Providing an implementation of the on_stop() method if the monitor cannot be stopped cooperatively from the run() method.

A basic monitor needs to implement the run() method, whose skeleton is often similar to the following:

void run()
{
  initialize_api();

  for (;;)
  {
    #ifdef HAVE_CXX_MUTEX
      unique_lock<mutex> run_guard(run_mutex);
      if (should_stop) break;
      run_guard.unlock();
    #endif

    scan_paths();
    wait_for_events();

    vector<change_events> evts = get_changes();
    vector<event> events;

    for (auto & evt : evts)
    {
      if (accept(evt.get_path))
      {
        events.push_back({event from evt});
      }
    }

    if (events.size()) notify_events(events);
  }

  terminate_api();
}

Despite being a minimal implementation, it performs all the tasks commonly performed by a monitor:

It initializes the API it uses to detect file system change events.
It enters a loop, often infinite, where change events are waited for.
If HAVE_CXX_MUTEX is defined, it locks on monitor::run_mutex to check whether monitor::should_stop is set to true. If it is, the monitor breaks the loop to return from run() as soon as possible.
It scans the paths that must be observed: this step might be necessary for example because some path may not have existed during the previous iteration of the loop, or because some API may require the user to re-register a watch on a path after events are retrieved.
Events are waited for and the wait should respect the specified latency.
Events are filtered to exclude those referring to paths that do not satisfy the configured filters.
The notify_events() method is called to filter the event types and notify the caller.

Constructor & Destructor Documentation

fsw::monitor::monitor	(	std::vector< std::string >	paths,
		FSW_EVENT_CALLBACK *	callback,
		void *	context = `nullptr`
	)

Constructs a monitor watching the specified paths.

The monitor will notify change events to the specified callback, passing it the pointer to the specified context.

Parameters

paths	The list of paths to watch.
callback	The callback to which change events will be notified. The callback cannot be null, otherwise a libfsw_exception will be thrown.
context	An optional pointer to context data. The monitor stores a copy of this pointer to pass it to the `callback`.

fsw::monitor::~monitor ( )

virtual

Destructs a monitor instance.

This destructor performs the following operations:

Stops the monitor.
Frees the compiled regular expression of the path filters, if any.

Warning: Destroying a monitor in the running state results in undefined behaviour.

See also: stop()

Member Function Documentation

bool fsw::monitor::accept_event_type ( fsw_event_flag event_type ) const

protected

Check whether an event should be accepted.

This function checks event_type against the event type filters of the monitor to determine whether it should be accepted.

Parameters

event_type The event type to check.

Returns: true if the event is accepted, false otherwise.

bool fsw::monitor::accept_path ( const std::string & path ) const

protected

Check whether a path should be accepted.

This function checks path against the path filters of the monitor to determine whether it should be accepted.

Parameters

event_type The path to check.

Returns: true if the path is accepted, false otherwise.

bool fsw::monitor::accept_path ( const char * path ) const

protected

Check whether a path should be accepted.

This function checks path against the path filters of the monitor to determine whether it should be accepted.

Parameters

event_type The path to check.

Returns: true if the path is accepted, false otherwise.

void fsw::monitor::add_event_type_filter ( const fsw_event_type_filter & filter )

Add an event type filter.

Adds a fsw_event_type_filter instance to filter events by type.

Parameters

filter The event type filter to add.

void fsw::monitor::add_filter ( const monitor_filter & filter )

Add a path filter.

This function adds a monitor_filter instance instance to the filter list.

Parameters

filter The filter to add.

vector< fsw_event_flag > fsw::monitor::filter_flags ( const event & evt ) const

protected

Filter event types.

This function filters the event types of an event leaving only the types allowed by the configured filters.

Parameters

evt	The event whose types must be filtered.

Returns: A vector containing the acceptable events.

void * fsw::monitor::get_context ( ) const

Get the pointer to the context data.

This function gets the pointer to the context data that is passed to the callback by the monitor.

Returns: The pointer to the context data.

string fsw::monitor::get_property ( std::string name )

Gets the value of a property.

This method gets the value of the property name. If the property name is not set, this method returns an empty string.

Parameters

name	The name of the property.

Returns: The value of the property.

bool fsw::monitor::is_running ( )

Check whether the monitor is running.

State is checked thread-safely locking on monitor::run_mutex.

Returns: true if the monitor is running, false otherwise.

void fsw::monitor::notify_events ( const std::vector< event > & events ) const

protected

Notify change events.

This function notifies change events using the provided callback.

See also: monitor()

void fsw::monitor::notify_overflow ( const std::string & path ) const

protected

Notify an overflow event.

This function notifies an overflow event using the provided callback.

Warning: Experiencing an overflow and the ability to notify it is an implementation-defined behaviour.

See also: monitor()

void fsw::monitor::on_stop ( )

protectedvirtual

Execute an implementation-specific stop handler.

This function is executed by the stop() method, after requesting the monitor to stop. This handler is required if the thread running run() is not able to preemptively stop its execution by checking the monitor::should_stop flag.

See also: stop()

Reimplemented in fsw::fsevents_monitor.

virtual void fsw::monitor::run ( )

protectedpure virtual

Execute monitor loop.

This function implements the monitor event watching logic. This function is called from start() and it is executed on its thread. This function should block until the monitoring loop terminates: when it returns, the monitor is marked as stopped.

This function should cooperatively check the monitor::should_stop field locking monitor::run_mutex and return if set to true.

See also: start(); stop()

Implemented in fsw::fen_monitor, fsw::inotify_monitor, fsw::kqueue_monitor, fsw::windows_monitor, fsw::fsevents_monitor, and fsw::poll_monitor.

void fsw::monitor::set_allow_overflow ( bool overflow )

Notify buffer overflows as change events.

If this flag is set, the monitor will report a monitor buffer overflow as a change event of type fsw_event_flag::Overflow.

Warning: The behaviour associated with this flag depends on the implementation.

Parameters

overflow true if overflow should be notified, false otherwise.

void fsw::monitor::set_context ( void * context )

Set the context data.

This function sets the pointer to the context data. The context data is opaque data that the monitor passes to the event callback.

Warning: The monitor stores the pointer to the context data throughout its life. The caller must ensure it points to valid data until the monitor is running.

Parameters

context The pointer to the context data.

void fsw::monitor::set_directory_only ( bool directory_only )

Watch directories only.

This function sets the directory only flag to the specified value. If this flag is set, then the monitor will only watch directories during a recursive scan. This functionality is only supported by monitors whose backend fires change events on a directory when one its children is changed. If a monitor backend does not support this functionality, the flag is ignored.

Warning: The behaviour associated with this flag depends on the implementation.

Parameters

directory_only true if only directories should be watched, flase otherwise.

void fsw::monitor::set_event_type_filters ( const std::vector< fsw_event_type_filter > & filters )

Set the event type filters.

This function sets the list of event type filters, substituting existing filters if any.

Parameters

filters The filters to set.

void fsw::monitor::set_filters ( const std::vector< monitor_filter > & filters )

Set the path filters.

This function sets the list of path filters, substituting existing filters if any.

Parameters

filters The filters to set.

void fsw::monitor::set_fire_idle_event ( bool fire_idle_event )

Sets the fire idle event flag.

When true, the fire idle event flag instructs the monitor to fire a fake event at the event of an idle cycle. An idle cycle is a period of time whose length is 110% of the monitor::latency where no change events were detected.

Parameters

fire_idle_event true if idle events should be fired, false otherwise.

void fsw::monitor::set_follow_symlinks ( bool follow )

Follow symlinks.

This function sets the follow_symlinks flag of the monitor to indicate whether the monitor should follow symbolic links or observe the links themselves.

Warning: The behaviour associated with this flag depends on the implementation.

Parameters

follow true if symbolic links should be followed, false otherwise.

void fsw::monitor::set_latency ( double latency )

Sets the latency.

This method sets the latency of the monitor to latency. The latency is a positive number that indicates to a monitor implementation how often events must be retrieved or waited for: the shortest the latency, the quicker events are processed.

Warning: The behaviour associated with this flag depends on the implementation.

Parameters

latency The latency value.

void fsw::monitor::set_properties ( const std::map< std::string, std::string > options )

Sets the custom properties.

This method replaces all the existing properties using the pairs contained into options.

Parameters

options The map containing the properties to set.

void fsw::monitor::set_property	(	const std::string &	name,
		const std::string &	value
	)

Sets a custom property.

This method sets the custom property name to value.

Parameters

name	The name of the property.
value	The value of the property.

void fsw::monitor::set_recursive ( bool recursive )

Recursively scan subdirectories.

This function sets the recursive flag of the monitor to indicate whether the monitor should recursively observe the contents of directories. The behaviour associated with this flag is an implementation-specific detail. This class only stores the value of the flag.

Warning: The behaviour associated with this flag depends on the implementation.

Parameters

recursive true if directories should be recursively, false otherwise.

void fsw::monitor::set_watch_access ( bool access )

Monitor file access.

Warning: The ability of monitoring file access depends on a monitor implementation.

void fsw::monitor::start ( )

Start the monitor.

The monitor status is marked as running and it starts watching for change events. This function performs the following tasks:

Atomically marks the thread state as running, locking on monitor::run_mutex.
Calls the run() function: the monitor::run_mutex is not locked during this call.
When run() returns, it atomically marks the thread state as stopped, locking on monitor::run_mutex.

This call does not return until the monitor is stopped and events are notified from its thread.

State changes are performed thread-safely locking on monitor::run_mutex.

See also: run(); stop()

void fsw::monitor::stop ( )

Stop the monitor.

This function asks the monitor to stop. Since start() is designed to execute the monitoring loop in its thread and to not return until the monitor is stopped, stop() is designed to be called from another thread. stop() is a cooperative signal that must be handled in an implementation-specific way in the run() function.

State changes are performed thread-safely locking on monitor::run_mutex.