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Symbian OS Kernel
The Symbian OS kernel provides the kernel functionality needed by Symbian OS, building on the simple threads and services provided by the nanokernel to provide more complex objects, such as user-mode threads, processes, reference-counted objects and handles, dynamically loaded libraries, inter-thread communication and more. These objects also include a range of more sophisticated synchronization objects:
- Symbian OS semaphores
- Symbian OS mutexes
Symbian OS semaphores are standard counting semaphores which support multiple
waiting threads and which release waiting threads in priority order.
Symbian OS mutexes are fully nestable (a thread can hold several mutexes at once, and can hold the same mutex multiple times). They also support priority inheritance: the holding thread inherits the priority of the highest priority waiting thread, if that is higher than its usual priority.
In contrast to the nanokernel, the Symbian OS kernel does allow dynamic memory allocation. It provides a kernel memory allocator – the kernel heap, which uses low-level memory services provided by an entity known as the memory model. The Symbian OS kernel is fully preemptible: an interrupt can cause it to reschedule at any point in its execution, even in the middle of a context switch. This means that the Symbian OS kernel can have no effect whatsoever on thread latency.