## repository: https://code.ros.org/svn/ros
<<PackageHeader(lockfree)>>
<<TOC(4)>>

The [[lockfree]] package contains [[http://en.wikipedia.org/wiki/Non-blocking_synchronization|lock-free data structures]] generally meant to be used in realtime or high-performance multithreaded systems.

Currently [[lockfree]] contains 2 data structures, [[http://www.ros.org/doc/api/lockfree/html/classlockfree_1_1FreeList.html|FreeList]] and [[http://www.ros.org/doc/api/lockfree/html/classlockfree_1_1ObjectPool.html|ObjectPool]].

== FreeList ==
The [[http://www.ros.org/doc/api/lockfree/html/classlockfree_1_1FreeList.html|FreeList]] class provides a fixed number of fixed-size blocks that you can allocate and free from multiple threads.  `FreeList` is lock-free but not wait-free.

=== Example ===
{{{
#!cplusplus
// Create a free list with 100 128-byte blocks
FreeList free_list(128, 100);
void* mem = free_list.allocate();

if (mem)
{
  ...

  free_list.free(mem);
}
}}}

== ObjectPool<T> ==
While the `FreeList` class simply provides allocation of specific-sized blocks of memory, the [[http://www.ros.org/doc/api/lockfree/html/classlockfree_1_1ObjectPool.html|ObjectPool]] class builds on top of that to provide allocation of specific object types, initialized using a template object.  It also allows you to allocate either `boost::shared_ptr`s or bare pointers, depending on your needs.  `ObjectPool` is lock-free but not wait-free.

=== Example ===
{{{
#!cplusplus
struct Foo
{
  std::vector<uint32_t> bar;
};

// Create a template object.  All objects in the pool will start initialized to this value.
// In realtime systems, for example, this lets you preallocate any vectors/strings/etc.
Foo template_object;
template_object.bar.resize(100);

// Construct a pool of 5 objects
ObjectPool<Foo> pool(5, template_object);

boost::shared_ptr<Foo> inst1 = pool.allocate();
if (inst1)
{
  ...
}

Foo* inst2 = pool.allocateBare();
if (inst2)
{
  ...
  pool.freeBare(inst2);
}
}}}

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