ecl_sigslots_lite Documentation

ecl_sigslots_lite

This avoids use of dynamic storage (malloc/new) and thread safety (mutexes) to provide a very simple sigslots implementation that can be used for *very* embedded development.

• Homepage: http://wiki.ros.org/ecl_sigslots_lite

Embedded Control Library

    This is a light version of ecl_sigslots and provides a 
    very ruthlessly simple signals and slots mechanisms useful for
     very* embedded development. You can read more about 
    signals and slots in the ecl_sigslots package.

Differences

    Some differences between from ecl_sigslots

    - Not thread safe...

    This is a bit of a vague statement on its own. In essence, its usually
    important to make sure your signals and slots finish processing any
    currently executing slots before they self destruct. Most sigslot 
    implementations dont do this, ecl_sigslots does, but ecl_sigslots_lite
    does not. If you have a monolothic program with a single thread, this
    probably doesn't matter, but if not, then you must take care to ensure
    signals and slots close appropriately. On the plus side, there is no
    dependency on platform api for mutexes. 

    - No disconnects...

    Adding disconnect capability adds alot of complexity to the sigslots
    implementation. Lite sigslots assume that signals and slots connections,
    once fixed until the signal goes out of scope. 

    - No dynamic storage (no heap storage with malloc/new)...

    This is often verboten with various embedded compilers and introduces
    alot of system overhead. Lite sigslots allocates memory up front and 
    will not permit overuse thereafter.

- Self contained...

While utilising things like standard error flag constructors (from ecl_errors)
might be convenient, this package is and likely will often be used 
standalone in a firmware project. As a result, its designed with its own
internal mechanisms (e.g. error class). This implies that a simple 'make
sources' (refer to ecl_build's documentation for more information) 
is sufficient to gather header and source files for direct inclusion into 
a firmware project.  

Compiling & Linking

    Include the following at the top of any translation unit which
    requires this library:

#include <ecl/sigslots_lite.hpp>

// Signals
using ecl::lite::Signal;

// Functions
using ecl::lite::connect
using ecl::lite::global_slots_stored;
using ecl::lite::global_slots_capacity;
using ecl::lite::member_slots_stored;
using ecl::lite::member_slots_capacity;

As its a template header library, you do not need to link.

Usage

Slots

    Users of lite sigslots don't actually directly use Slot classes (unlike ecl_sigslots).
    Slots are still there, but they are stored behind the scenes, either in a global slots
    manager or member slots manager inherited by a class.

Storage Capacities

    Signals and slots need to reserve memory before usage. For global slots, you need to 
    set a static variable before making any connections to slots of that type.

// allocate for global function slots with const char* and void arg footprints
template<> const unsigned int ecl::lite::GlobalSlots<const char*>::capacity = 4;
template<> const unsigned int ecl::lite::GlobalSlots<void>::capacity = 2;

int main() {
    // ...

For member slots, your class needs to inherit from the MemberSlots interface and specify the capacity as a template parameter (default is 1).

    class Foo : public ecl::lite::MemberSlots<const char*,Foo>,
                    public ecl::lite::MemberSlots<void,Foo,2>
{
public:
            Foo() {}

            void f(const char* str) { /* */ }
            void g() { /* */ }
            void h() { /* */ }
    };

For signals, simply specify the capacity template parameter (again default is 1) when instantiating the signal. This reflects the number of connections it can handle.

ecl::lite::Signal<const char*, 2> signal;

Connections

    Connections are made via the connect functions, linking directly to the function
    pointers.

connect(signal,f);            // connecting to a global slot
connect(signal,&Foo::f, foo); // connecting to a member slot

Utilities

    There are some utility functions for debugging.

// statistics for global slots with arg type 'const char*'
std::cout << ecl::lite::global_slots_stored<const char*>() << std::endl;
std::cout << ecl::lite::global_slots_capacity<const char*>() << std::endl;

// statistics for global slots with no args
std::cout << ecl::lite::global_slots_stored<void>() << std::endl;
std::cout << ecl::lite::global_slots_capacity<void>() << std::endl;

// statistics for member slots of foo with no args
std::cout << ecl::lite::member_slots_stored<void>(foo) << std::endl;
std::cout << ecl::lite::member_slots_capacity<void>(foo) << std::endl;

Examples

    These are more of a rough coverage test.

    - src/examples/sigslots.cpp

ChangeLog

    - <b>Mar 11</b> : redesigned to be self contained.
    - <b>Feb 11</b> : prototype implementation tested.