micro_os_plus::utils::static_double_list_links Class Reference

A class for the core of a statically allocated doubly linked list (pointers to neighbours). More...

#include <micro-os-plus/utils/lists.h>

Inheritance diagram for micro_os_plus::utils::static_double_list_links:

Public Types
using	is_statically_allocated = std::true_type
	Type indicating that the links node is statically allocated.

Public Member Functions
constexpr	static_double_list_links ()
	Construct a statically allocated list node (bss initialised).
constexpr	~static_double_list_links ()
	Destruct the node.
constexpr void	initialize (void)
	Initialise the node links.
void	initialize_once (void)
	Initialize the list only at first run.
void	link_next (double_list_links_base *node)
	Link the new node as next.
void	link_previous (double_list_links_base *node)
	Link the new node as previous.
bool	linked (void) const
	Check if the node is linked to a double list.
constexpr double_list_links_base *	next (void) const
	Get the link to the next node.
void	nullify (void)
	Reset the two pointers to nullptr.
constexpr double_list_links_base *	previous (void) const
	Get the link to the previous node.
bool	uninitialized (void) const
	Check if the node is uninitialised.
void	unlink (void)
	Remove this node from the list.

Protected Attributes
double_list_links_base *	next_
	Pointer to the next node.
double_list_links_base *	previous_
	Pointer to the previous node.

Detailed Description

A class for the core of a statically allocated doubly linked list (pointers to neighbours).

The pair of uninitialised pointers to the next and previous list elements and the methods to access the pointers are inherited from the base class.

It is expected that instances of this class to be statically allocated in the bss section and cleared (set to zero) during startup.

These peculiar types of lists are used by registrars, to automate the self-registration of other statically allocated objects, like drivers, threads, etc.

Since the order of static constructors is not defined, it is perfectly and legally possible that the constructor of the registrar will be invoked after the constructors of the objects that need to register into the list, thus the registrar must be guaranteed to be initialised before running any static constructors.

The solution is to design the object in such a way as to benefit from the standard bss initialisation, in other words take nullptr as starting values.

In practical terms, the list initialisation cannot be done in the constructor, but must be manually done before any method that adds elements to the list is called.

Definition at line 323 of file lists.h.

Member Typedef Documentation

is_statically_allocated

using micro_os_plus::utils::static_double_list_links::is_statically_allocated = std::true_type

Type indicating that the links node is statically allocated.

Definition at line 329 of file lists.h.

Constructor & Destructor Documentation

static_double_list_links()

micro_os_plus::utils::static_double_list_links::static_double_list_links ( )

constexpr

Construct a statically allocated list node (bss initialised).

As the name implies, it is assumed that the instance of the object is allocated statically and the entire content was set to zero during startup (via BSS init).

This is equivalent to setting the pointers to nullptr.

Warning

Code analysis may trigger:

• Member previous_ was not initialized in constructor
• Member next_ was not initialized in constructor

Definition at line 132 of file inlines.h.

~static_double_list_links()

micro_os_plus::utils::static_double_list_links::~static_double_list_links ( )

constexpr

Destruct the node.

Warning

The code to clear the pointers is now commented out, since recent GCC optimizes it out (dead store elimination). Depending on the version, there might be some attributes to allow this, but they are not safe, for example
__attribute__((optimize("no-lifetime-dse,no-dse,no-inline"))) did not help. The workaround is to use nullify() explicitly, or, even better, to clear the memory before invoking the placement new constructor again.

Definition at line 155 of file inlines.h.

Member Function Documentation

initialize()

void micro_os_plus::utils::double_list_links_base::initialize ( void )

constexprinherited

Initialise the node links.

Parameters

None.

Returns

Nothing.

Set both pointers to point to this node.

This is the definition of an unlinked node.

Note

After unlinking the node from a list, it must be returned to this state.

Definition at line 91 of file inlines.h.

initialize_once()

void micro_os_plus::utils::double_list_links_base::initialize_once ( void )

inherited

Initialize the list only at first run.

Parameters

None.

Returns

Nothing.

If the statically allocated list is still in the initial uninitialised state (with both pointers nullptr), initialise the list to the empty state, with both pointers pointing to itself.

For non-statically initialised lists, this method is ineffective, since the node is always initialised at construct time.

Note

This method must be manually called for statically allocated list before inserting elements, or performing any other operations.

Definition at line 85 of file lists.cpp.

link_next()

void micro_os_plus::utils::double_list_links_base::link_next ( double_list_links_base * node )

inherited

Link the new node as next.

Parameters

None.

Returns

Nothing.

Insert the new node between the next pointer and the node pointed by it.

Used by lists to link new nodes to the list head.

Definition at line 101 of file lists.cpp.

link_previous()

void micro_os_plus::utils::double_list_links_base::link_previous ( double_list_links_base * node )

inherited

Link the new node as previous.

Parameters

None.

Returns

Nothing.

Insert the new node between the previous pointer and the node pointed by it.

Used by lists to link new nodes to the list tail.

Definition at line 125 of file lists.cpp.

linked()

bool micro_os_plus::utils::double_list_links_base::linked ( void ) const

inherited

Check if the node is linked to a double list.

Return values

true	The node is linked with both pointers.
false	The node is not linked.

To be linked, both pointers must point to different nodes than itself (double list requirement).

Definition at line 173 of file lists.cpp.

next()

double_list_links_base * micro_os_plus::utils::double_list_links_base::next ( void ) const

constexprinherited

Get the link to the next node.

Return values

Pointer

to the next node.

Definition at line 104 of file inlines.h.

nullify()

void micro_os_plus::utils::static_double_list_links::nullify

(

void

)

Reset the two pointers to nullptr.

Parameters

None.

Returns

Nothing.

Warning

Not very safe, since the compiler may optimise out the code.

Definition at line 196 of file lists.cpp.

previous()

double_list_links_base * micro_os_plus::utils::double_list_links_base::previous ( void ) const

constexprinherited

Get the link to the previous node.

Return values

Pointer

to the previous node.

Definition at line 110 of file inlines.h.

uninitialized()

bool micro_os_plus::utils::double_list_links_base::uninitialized ( void ) const

inherited

Check if the node is uninitialised.

Parameters

None.

Return values

true	The links are not initialised.
false	The links are initialised.

An uninitialized node is a node with the pointers set to nullptr.

Only statically allocated nodes in the initial state are uninitialized. Regular nodes are always initialised.

Definition at line 58 of file lists.cpp.

unlink()

void micro_os_plus::utils::double_list_links_base::unlink ( void )

inherited

Remove this node from the list.

Returns

Nothing.

Update both neighbours to point to each other, practically removing the node from the list.

The node is returned to the initial state (empty), with both pointers pointing to itself.

Definition at line 150 of file lists.cpp.

Member Data Documentation

next_

double_list_links_base* micro_os_plus::utils::double_list_links_base::next_

protectedinherited

Pointer to the next node.

Definition at line 231 of file lists.h.

previous_

double_list_links_base* micro_os_plus::utils::double_list_links_base::previous_

protectedinherited

Pointer to the previous node.

Definition at line 226 of file lists.h.

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

• lists.h
• inlines.h
• lists.cpp