350 lines
11 KiB
C
350 lines
11 KiB
C
/***************************************************************************
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* __________ __ ___.
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* Open \______ \ ____ ____ | | _\_ |__ _______ ___
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* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
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* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
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* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
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* \/ \/ \/ \/ \/
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* $Id$
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*
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* Copyright (C) 2014 by Michael Sevakis
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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* KIND, either express or implied.
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*
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****************************************************************************/
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#include "kernel-internal.h"
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#include <string.h>
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#include "mrsw_lock.h"
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#ifdef HAVE_PRIORITY_SCHEDULING
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static FORCE_INLINE void
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mrsw_reader_claim(struct mrsw_lock *mrsw, struct thread_entry *current,
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int count, unsigned int slotnum)
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{
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/* no need to lock this; if a reader can claim, noone is in the queue */
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threadbit_set_bit(&mrsw->splay.mask, slotnum);
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mrsw->splay.blocker.thread = count == 1 ? current : NULL;
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}
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static FORCE_INLINE void
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mrsw_reader_relinquish(struct mrsw_lock *mrsw, struct thread_entry *current,
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struct thread_entry *first, int count,
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unsigned int slotnum)
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{
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/* If no writer is queued or has ownership then noone is queued;
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if a writer owns it, then the reader would be blocked instead.
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Therefore, if the queue has threads, then the next after the
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owning readers is a writer and this is not the last reader. */
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if (first)
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corelock_lock(&mrsw->splay.cl);
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threadbit_clear_bit(&mrsw->splay.mask, slotnum);
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if (count == 0)
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{
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/* There is noone waiting; we'd be calling mrsw_wakeup_writer()
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at this time instead */
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mrsw->splay.blocker.thread = NULL;
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return;
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}
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if (count == 1)
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{
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KERNEL_ASSERT(threadbit_popcount(&mrsw->splay.mask) == 1,
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"mrsw_reader_relinquish() - "
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"threadbits has wrong popcount: %d\n",
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threadbit_popcount(&mrsw->splay.mask));
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/* switch owner to sole remaining reader */
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slotnum = threadbit_ffs(&mrsw->splay.mask);
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mrsw->splay.blocker.thread = __thread_slot_entry(slotnum);
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}
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if (first)
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{
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priority_disinherit(current, &mrsw->splay.blocker);
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corelock_unlock(&mrsw->splay.cl);
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}
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}
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static FORCE_INLINE unsigned int
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mrsw_reader_wakeup_writer(struct mrsw_lock *mrsw, struct thread_entry *thread,
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unsigned int slotnum)
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{
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threadbit_clear_bit(&mrsw->splay.mask, slotnum);
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return wakeup_thread(thread, WAKEUP_TRANSFER);
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}
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static FORCE_INLINE unsigned int
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mrsw_writer_wakeup_writer(struct mrsw_lock *mrsw, struct thread_entry *thread)
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{
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return wakeup_thread(thread, WAKEUP_TRANSFER);
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(void)mrsw;
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}
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static FORCE_INLINE unsigned int
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mrsw_writer_wakeup_readers(struct mrsw_lock *mrsw, struct thread_entry *first)
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{
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unsigned int result = wakeup_thread(first, WAKEUP_TRANSFER_MULTI);
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mrsw->count = __running_self_entry()->retval;
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return result;
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}
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#else /* !HAVE_PRIORITY_SCHEDULING */
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#define mrsw_reader_claim(mrsw, current, count, slotnum) \
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do {} while (0)
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#define mrsw_reader_relinquish(mrsw, current, first, count, slotnum) \
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do {} while (0)
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static FORCE_INLINE unsigned int
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mrsw_reader_wakeup_writer(struct mrsw_lock *mrsw, struct thread_entry *thread)
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{
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mrsw->splay.blocker.thread = thread;
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return wakeup_thread(thread);
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}
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static FORCE_INLINE unsigned int
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mrsw_writer_wakeup_writer(struct mrsw_lock *mrsw, struct thread_entry *thread)
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{
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mrsw->splay.blocker.thread = thread;
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return wakeup_thread(thread);
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}
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static FORCE_INLINE unsigned int
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mrsw_writer_wakeup_readers(struct mrsw_lock *mrsw, struct thread_entry *first)
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{
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mrsw->splay.blocker.thread = NULL;
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int count = 1;
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while (1)
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{
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wakeup_thread(first);
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if (!(first = WQ_THREAD_FIRST(&mrsw->queue)) || first->retval == 0)
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break;
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count++;
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}
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mrsw->count = count;
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return THREAD_OK;
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}
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#endif /* HAVE_PRIORITY_SCHEDULING */
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/** Public interface **/
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/* Initializes a multi-reader, single-writer object */
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void mrsw_init(struct mrsw_lock *mrsw)
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{
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mrsw->count = 0;
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wait_queue_init(&mrsw->queue);
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blocker_splay_init(&mrsw->splay);
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#ifdef HAVE_PRIORITY_SCHEDULING
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memset(mrsw->rdrecursion, 0, sizeof (mrsw->rdrecursion));
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#endif
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corelock_init(&mrsw->cl);
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}
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/* Request reader thread lock. Any number of reader threads may enter which
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* also locks-out all writer threads. Same thread may safely acquire read
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* access recursively. The current writer is ignored and gets access. */
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void mrsw_read_acquire(struct mrsw_lock *mrsw)
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{
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ASSERT_CPU_MODE(CPU_MODE_THREAD_CONTEXT);
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struct thread_entry *current = __running_self_entry();
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if (current == mrsw->splay.blocker.thread IF_PRIO( && mrsw->count < 0 ))
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return; /* Read request while holding write access; pass */
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#ifdef HAVE_PRIORITY_SCHEDULING
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/* Track recursion counts for each thread:
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IF_PRIO, mrsw->count just tracks unique owners */
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unsigned int slotnum = THREAD_ID_SLOT(current->id);
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if (threadbit_test_bit(&mrsw->splay.mask, slotnum))
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{
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KERNEL_ASSERT(mrsw->rdrecursion[slotnum] < UINT8_MAX,
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"mrsw_read_acquire() - "
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"Thread %s did too many claims\n",
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current->name);
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mrsw->rdrecursion[slotnum]++;
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return;
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}
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#endif /* HAVE_PRIORITY_SCHEDULING */
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corelock_lock(&mrsw->cl);
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int count = mrsw->count;
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if (LIKELY(count >= 0 && mrsw->queue.head == NULL))
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{
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/* Lock open to readers:
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IFN_PRIO, mrsw->count tracks reader recursion */
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mrsw->count = ++count;
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mrsw_reader_claim(mrsw, current, count, slotnum);
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corelock_unlock(&mrsw->cl);
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return;
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}
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/* A writer owns it or is waiting; block... */
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current->retval = 1; /* indicate multi-wake candidate */
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disable_irq();
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block_thread(current, TIMEOUT_BLOCK, &mrsw->queue, &mrsw->splay.blocker);
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corelock_unlock(&mrsw->cl);
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/* ...and turn control over to next thread */
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switch_thread();
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}
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/* Release reader thread lockout of writer thread. The last reader to
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* leave opens up access to writer threads. The current writer is ignored. */
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void mrsw_read_release(struct mrsw_lock *mrsw)
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{
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struct thread_entry *current = __running_self_entry();
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if (current == mrsw->splay.blocker.thread IF_PRIO( && mrsw->count < 0 ))
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return; /* Read release while holding write access; ignore */
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#ifdef HAVE_PRIORITY_SCHEDULING
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unsigned int slotnum = THREAD_ID_SLOT(current->id);
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KERNEL_ASSERT(threadbit_test_bit(&mrsw->splay.mask, slotnum),
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"mrsw_read_release() -"
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" thread '%s' not reader\n",
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current->name);
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uint8_t *rdcountp = &mrsw->rdrecursion[slotnum];
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unsigned int rdcount = *rdcountp;
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if (rdcount > 0)
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{
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/* Reader is releasing recursive claim */
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*rdcountp = rdcount - 1;
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return;
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}
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#endif /* HAVE_PRIORITY_SCHEDULING */
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corelock_lock(&mrsw->cl);
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int count = mrsw->count;
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KERNEL_ASSERT(count > 0, "mrsw_read_release() - no readers!\n");
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unsigned int result = THREAD_NONE;
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const int oldlevel = disable_irq_save();
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struct thread_entry *thread = WQ_THREAD_FIRST(&mrsw->queue);
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if (--count == 0 && thread != NULL)
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{
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/* No readers remain and a writer is waiting */
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mrsw->count = -1;
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result = mrsw_reader_wakeup_writer(mrsw, thread IF_PRIO(, slotnum));
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}
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else
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{
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/* Giving up readership; we may be the last, or not */
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mrsw->count = count;
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mrsw_reader_relinquish(mrsw, current, thread, count, slotnum);
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}
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restore_irq(oldlevel);
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corelock_unlock(&mrsw->cl);
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#ifdef HAVE_PRIORITY_SCHEDULING
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if (result & THREAD_SWITCH)
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switch_thread();
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#endif /* HAVE_PRIORITY_SCHEDULING */
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(void)result;
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}
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/* Acquire writer thread lock which provides exclusive access. If a thread
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* that is holding read access calls this it will deadlock. The writer may
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* safely call recursively. */
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void mrsw_write_acquire(struct mrsw_lock *mrsw)
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{
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ASSERT_CPU_MODE(CPU_MODE_THREAD_CONTEXT);
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struct thread_entry *current = __running_self_entry();
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if (current == mrsw->splay.blocker.thread)
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{
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/* Current thread already has write access */
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mrsw->count--;
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return;
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}
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corelock_lock(&mrsw->cl);
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int count = mrsw->count;
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if (LIKELY(count == 0))
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{
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/* Lock is open to a writer */
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mrsw->count = -1;
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mrsw->splay.blocker.thread = current;
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corelock_unlock(&mrsw->cl);
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return;
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}
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/* Readers present or a writer owns it - block... */
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current->retval = 0; /* indicate single-wake candidate */
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disable_irq();
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block_thread(current, TIMEOUT_BLOCK, &mrsw->queue, &mrsw->splay.blocker);
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corelock_unlock(&mrsw->cl);
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/* ...and turn control over to next thread */
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switch_thread();
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}
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/* Release writer thread lock and open the lock to readers and writers */
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void mrsw_write_release(struct mrsw_lock *mrsw)
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{
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KERNEL_ASSERT(__running_self_entry() == mrsw->splay.blocker.thread,
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"mrsw_write_release->wrong thread (%s != %s)\n",
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__running_self_entry()->name,
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mrsw->splay.blocker.thread->name);
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int count = mrsw->count;
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if (count < -1)
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{
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/* This thread still owns write lock */
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mrsw->count = count + 1;
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return;
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}
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unsigned int result = THREAD_NONE;
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corelock_lock(&mrsw->cl);
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const int oldlevel = disable_irq_save();
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struct thread_entry *thread = WQ_THREAD_FIRST(&mrsw->queue);
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if (thread == NULL) /* 'count' becomes zero */
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{
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mrsw->splay.blocker.thread = NULL;
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mrsw->count = 0;
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}
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else if (thread->retval == 0) /* 'count' stays -1 */
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result = mrsw_writer_wakeup_writer(mrsw, thread);
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else /* 'count' becomes # of readers */
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result = mrsw_writer_wakeup_readers(mrsw, thread);
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restore_irq(oldlevel);
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corelock_unlock(&mrsw->cl);
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#ifdef HAVE_PRIORITY_SCHEDULING
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if (result & THREAD_SWITCH)
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switch_thread();
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#endif /* HAVE_PRIORITY_SCHEDULING */
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(void)result;
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}
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