Data Structures
Zephyr provides a library of common general purpose data structures used within the kernel, but useful by application code in general. These include list and balanced tree structures for storing ordered data, and a ring buffer for managing “byte stream” data in a clean way.
Note that in general, the collections are implemented as “intrusive” data structures. The “node” data is the only struct used by the library code, and it does not store a pointer or other metadata to indicate what user data is “owned” by that node. Instead, the expectation is that the node will be itself embedded within a user-defined struct. Macros are provided to retrieve a user struct address from the embedded node pointer in a clean way. The purpose behind this design is to allow the collections to be used in contexts where dynamic allocation is disallowed (i.e. there is no need to allocate node objects because the memory is provided by the user).
Note also that these libraries are generally unsynchronized; access to them is not threadsafe by default. These are data structures, not synchronization primitives. The expectation is that any locking needed will be provided by the user. Some of the provided data structures are thread safe in specific usage scenarios (see Single Producer Single Consumer Lock Free Queue and Multi Producer Single Consumer Lock Free Queue).