Move the storage for the thread queue heads to the threads. Each thread
provides a set of thread queue heads allocated from a dedicated memory
pool. In case a thread blocks on a queue, then it lends its heads to
the queue. In case the thread unblocks, then it takes a free set of
threads from the queue. Since a thread can block on at most one queue
this works. This mechanism is used in FreeBSD. The motivation for this
change is to reduce the memory demands of the synchronization objects.
On a 32-bit uni-processor configuration the Thread_queue_Control size is
now 8 bytes, compared to 64 bytes in RTEMS 4.10 (other changes reduced
the size as well).
--
Overview of newlib support (newlib is from CYGNUS)
Each task can have its own libc state including:
open stdio files
strtok
multi precision arithmetic state
etc.
This is implemented by a reentrancy data structure for each task.
When a task is "started" (in RTEMS sense) the reentrancy structure
is allocated. Its address is stored in notepad[NOTEPAD_LAST].
When task is switched to, the value of global variable _impure_ptr
is changed to the value of the new tasks reentrancy structure.
When a task is deleted
atexit() processing (for that task) happens
task's stdio buffers are flushed
When exit(3) is called
calling task's atexit processing done
global libc state atexit processing done
(this will include any atexit routines installed by drivers)
executive is shutdown
causes a context switch back to bsp land
NOTE:
libc extension are installed by bsp_libc_init()
iff we are using clock interrupts.
This hack is necessary to allow the tmtests to avoid
timing the extensions.
Sebastian Huber
d7665823b2