README.md

Eclipse iceoryx hoofs overview

The iceoryx hoofs (Handy Objects Optimised For Safety) are our basic building blocks - the foundation of iceoryx. There are a wide variety of building blocks grouped together in categories or namespace, depending on where or how they are used.

Categories

Namespace	Short Description
cxx	Since we are not allowed to use C++17 as well as the heap or exceptions we implemented constructs like optional, expected or variant so that we can be as modern as possible. Furthermore, you can find here constructs which are mentioned in the C++ Core Guidelines as well as STL re-implementations of container like vector which are relocatable an can be placed into the shared memory.
concurrent	You should never use concurrent constructs like mutex, semaphores, atomic etc directly in our codebase. At the moment we still have some exceptions to this guideline but the idea is that all classes which are using them are stored under concurrent and have to undergo more tests then the usual non concurrent class. For instance we try to provide stress tests for them. In here you can find fifo, smart_lock, sofi, trigger_queue and much more.
design_pattern	Certain code patterns which are repeating themselves all over the code are abstracted and stored in here. At the moment we only have the creation pattern but maybe there will be more.
error-handling	The Error-Handler to in iceoryx for handling fault cases.
log	The logger used by iceoryx.
posix_wrapper	Posix constructs like shared memory, threads or semaphores are not used directly in our code base. We abstracted them so that they are following the RAII (Resource Acquisition Is Initialization) idiom and other good practices from the C++ community.
units
other	There are even more namespaces inside the iceoryx hoofs but they will either become obsolete in the future, will be integrated into existing names or are established as another namespace and documented here. We are unsure where they will end up in the future.

Structure

The following sections have a column called internal to indicate that the API is not stable and can change anytime. You should never rely on it and you get no support if you do and your code does not compile after a pull request.

The column maybe obsolete marks classes which can be removed anytime soon.

CXX

STL constructs which are not in the C++11 standard included are contained here as well as constructs which are helping us in our daily life. We differ in here from our coding guidelines and follow the C++ STL coding guidelines to help the user to have a painless transition from the official STL types to ours. The API should also be identical to the corresponding STL types but we have to make exceptions here. For instance, we do not throw exceptions, try to avoid undefined behavior and we do not use dynamic memory. In these cases we adjusted the API to our use case.

Most of the headers are providing some example code on how the class should be used.

class/file	internal	maybe obsolete	description
algorithm			Implements min and max for an arbitrary number of values of the same type. For instance min(1,2,3,4,5);
attributes			C++17 and C++20 attributes are sometimes available through compiler extensions. The attribute macros defined in here (like IOX_FALLTHROUGH, IOX_MAYBE_UNUSED ... ) make sure that we are able to use them if the compiler supports it.
convert			Converting a number into a string is easy, converting it back can be hard. You can use functions like strtoll but you still have to handle errors like under- and overflow, or converting invalid strings into number. Here we abstract all the error handling so that you can convert strings into numbers safely.
expected			Our base class used in error handling. Every function which can fail should return an expected. With this the user knows that this function can fail and that they have to do some kind of error handling. We got inspired by the C++ expected proposal and by the rust error handling concept.
filesystem			Implementation of C++17 filesystem features for instance cxx::perms to abstract file permissions
forward_list			Heap and exception free, relocatable implementation of std::forward_list
function_ref			C++11 implementation of the next-gen C++ feature std::function_ref see function_ref proposal. It behaves like std::function but does not own the callable.
GenericRAII			This is an abstraction of the C++ RAII idiom. Sometimes you have constructs where you would like to perform a certain task on creation and then again when they are getting out of scope, this is where GenericRAII comes in. It is like a std::lock_guard or a std::shared_ptr but more generic.
helplets			Implementations of C++ Core Guideline concepts like not_null Ensures Expects are contained here. Additionally, we are providing some types to verify preconditions at compile time. Think of an int which has to be always greater 5, here we provide types like greater_or_equal<int, 6>.
list			Heap and exception free, relocatable implementation of std::list
MethodCallback			Constructs a MethodCallback from a pointer to a specific object and a pointer to a method of that object, also as ConstMethodCallback available
NewType<T, Policies>			C++11 implementation of Haskells NewType-pattern.
optional			C++11 implementation of the C++17 feature std::optional
pair	i	X	Simplistic re-implementation of an std::pair It maybe becomes obsolete.
poor_mans_heap			Acquires memory on the stack for placement new instantiations. All classes must inherit from a base class which has to be known at compile time but the class itself does not have to be known - only the size.
ReferenceCounter	i		Basic building block for classes which are needing some kind of reference counting like a std::shared_ptr
serialization		X	Implements a simple serialization concept for classes based on the idea presented here ISOCPP serialization.
set	i	X	Templated helper functions to create a fake std::set from a vector.
string			Heap and exception free implementation of std::string. Attention, since the string is stack based, std::string or char array which are assigned to this string will be truncated and zero-terminated if they exceed the string capacity.
type_traits			Extended support for evaluating types on compile-time.
types			Declares essential building block types like byte_t.
unique_ptr			Provides a heap-less unique ptr implementation, unlike the STL
variant			C++11 implementation of the C++17 feature std::variant
variant_queue			A queue which wraps multiple variants of Queues (FiFo, SoFi, ResizeableLockFreeQueue)
vector			Heap and exception free implementation of std::vector

Concurrent

If you have to write concurrent code, never use concurrency constructs like mutex, atomic, thread, semaphore etc. directly. Most of the use cases can be solved by using an ActiveObject which uses as building block our FiFo or a queue which is thread-safe when combined with smart_lock. To learn more about active objects see Prefer Using Active Objects Instead Of Naked Threads.

class	internal	maybe obsolete	description
ActiveObject	i	X	Active object base skeleton implementation inspired by Prefer Using Active Objects Instead Of Naked Threads
FiFo	i		Single Producer, Single Consumer Lock Free FiFo
LoFFLi	i		Lock-free LIFO based index manager (Lock Free Free List). One building block of our memory manager. After construction it contains the indices {0 ... n} which you can acquire and release.
PeriodicTask	i		Periodically executes a callable specified by the template parameter in a configurable time interval.
smart_lock	i		Creates arbitrary thread safe constructs which then can be used like smart pointers. If some STL type should be thread safe use the smart_lock to create the thread safe version in one line. Based on some ideas presented in Wrapping C++ Member Function Calls
SoFi	i		Single Producer, Single Consumer Lock Free Safely overflowing FiFo (SoFi).
TACO	i		Thread Aware exChange Ownership (TACO). Solution if you would like to use std::atomic with data types larger than 64 bit. Wait free data synchronization mechanism between threads.
TriggerQueue	i	X	Queue with a push - pop interface where pop is blocking as long as the queue is empty. Can be used as a building block for active objects.

attribute overview of the available Queues:

Data Structure	Shared Memory usable	Thread-Safe	Lock-Free	Concurrent Producers : Consumers	Bounded Capacity	Data Type Restriction	Use Case
FiFo	Yes	Yes	Yes	1:1	Yes	Copyable	FIFO Data transfer
LockfreeQueue	Yes	Yes	Yes	n:m	Yes	Copyable or Movable	lock-free transfer of arbitrary data between multiple contexts in FIFO order with overflow handling (ringbuffer)
LoFFLi	Yes	Yes	Yes	n:m	Yes	int32	manage memory access, LIFO order
smart_lock	Yes	Yes	No	n/a	n/a	None	Wrapper to make classes thread-safe (by using a lock)
SoFi	Yes	Yes	Yes	1:1	Yes	Trivially Copyable	lock-free transfer of small data (e.g. pointers) between two contexts in FIFO order with overflow handling (ringbuffer)
TACO	Yes	Yes	Yes	n:m	Yes	Copyable or Movable	fast lock-free exchange data between threads
TriggerQueue	No	Yes	No	n:m	Yes	Copyable	Process events in a blocking way

Design pattern

class	internal	maybe obsolete	description
Creation			When implementing resource handling classes which follow the RAII idiom we may have to throw exceptions inside the constructor. As an alternative to exceptions we have the creation pattern, a specialized factory which returns the object inside of an expected.
Command	i		Base class for void(Arg) calls - known as commands.

Error handling

The Error-Handler is a central instance for collecting al errors and react to them. In the file error-handling.hpp are all error enums collected. The Error-Handler has different error-levels, for more information see error-handling.md

class	internal	maybe obsolete	description
errorHandler			Free function to call the Error-Handler with a defined error and an error-level, see header file for practical example.
ErrorHandler	i		ErrorHandler class only for testing purposes, should not be used directly

Log

For information about how to use the logger API see error-handling.md

class	internal	maybe obsolete	description
logger

POSIX wrapper

We abstract POSIX resources following the RAII idiom and by using our Creation pattern. Try to exclusively use these abstractions or add a new one when using POSIX resources like semaphores, shared memory, etc.

class	internal	maybe obsolete	description
AccessController	i		Interface for Access Control Lists (ACL).
IpcChannel	i		Helper types used by the MessageQueueand the UnixDomainSocket.
MessageQueue	i		Interface for Message Queues, see ManPage mq_overview.
mutex	i		Mutex interface, see ManPage pthread_mutex_lock.
posix_access_rights			Rights and user management interface.
posixCall			Wrapper around C and POSIX function calls which performs a full error handling. Additionally, this wrapper makes sure that EINTR handling is performed correctly by repeating the system call.
Semaphore			Semaphore interface, see ManPage sem_overview
shared_memory_object/Allocator	i		Helper class for the SharedMemoryObject.
shared_memory_object/MemoryMap	i		Abstraction of mmap, munmap and helper class for the SharedMemoryObject.
shared_memory_object/SharedMemory	i		Abstraction of shared memory, see ManPage shm_overview and helper class for the SharedMemoryObject.
SharedMemoryObject	i		Creates and maps existing shared memory into the application.
system_configuration	i		Collection of free functions which acquire system information like the page-size.
thread			Wrapper for pthread functions like pthread_setname_np.
Timer			Interface for the posix timer, see ManPage timer_create.
UnixDomainSocket	i		Interface for unix domain sockets.

Units

Never use physical properties like speed or time directly as integer or float in your code. Otherwise you encounter problems like this function void setTimeout(int timeout). What is the unit of the argument, seconds? minutes? If you use our Duration you see it directly in the code.

void setTimeout(const Duration & timeout);

setTimeout(11_s); // 11 seconds
setTimeout(5_ms); // 5 milliseconds

class	internal	maybe obsolete	description
Duration	i		Represents the unit time, is convertable to timespec, timeval and std::chrono. Uses user defined literals for readability.

objectpool

class	internal	maybe obsolete	description
ObjectPool	i		Container which stores raw objects without calling the ctor of the objects.

graphs

class	internal	maybe obsolete	description
DirectedGraph	i		Creates and manages a directed graph.
DirectedAcyclicGraph	i		Like the DirectedGraph but additional checks prohibit to create edges which have a cyclic dependency.

file-reader

class	internal	maybe obsolete	description
FileReader	i	x	Wrapper for opening files and reading them. Maybe not needed.

[Check out iceoryx_hoofs on GitHub :fontawesome-brands-github:](https://github.com/eclipse-iceoryx/iceoryx/tree/master/iceoryx_hoofs/){ .md-button }