haiku/src/system/kernel/lock.cpp

/*
 * Copyright 2008, Ingo Weinhold, ingo_weinhold@gmx.de.
 * Copyright 2002-2008, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
 * Distributed under the terms of the MIT License.
 *
 * Copyright 2001-2002, Travis Geiselbrecht. All rights reserved.
 * Distributed under the terms of the NewOS License.
 */

/* Mutex and recursive_lock code */

#include <lock.h>

#include <stdlib.h>
#include <string.h>

#include <OS.h>

#include <debug.h>
#include <int.h>
#include <kernel.h>
#include <thread.h>
#include <util/AutoLock.h>


struct mutex_waiter {
	struct thread*	thread;
	mutex_waiter*	next;		// next in queue
	mutex_waiter*	last;		// last in queue (valid for the first in queue)
};

struct rw_lock_waiter {
	struct thread*	thread;
	rw_lock_waiter*	next;		// next in queue
	rw_lock_waiter*	last;		// last in queue (valid for the first in queue)
	bool			writer;
};

#define MUTEX_FLAG_OWNS_NAME	MUTEX_FLAG_CLONE_NAME
#define MUTEX_FLAG_RELEASED		0x2

#define RW_LOCK_FLAG_OWNS_NAME	RW_LOCK_FLAG_CLONE_NAME


#ifdef KDEBUG
#	define RECURSIVE_LOCK_HOLDER(lock)	((lock)->lock.holder)
#else
#	define RECURSIVE_LOCK_HOLDER(lock)	((lock)->holder)
#endif


int32
recursive_lock_get_recursion(recursive_lock *lock)
{
	if (RECURSIVE_LOCK_HOLDER(lock) == thread_get_current_thread_id())
		return lock->recursion;

	return -1;
}


void
recursive_lock_init(recursive_lock *lock, const char *name)
{
	mutex_init(&lock->lock, name != NULL ? name : "recursive lock");
	RECURSIVE_LOCK_HOLDER(lock) = -1;
	lock->recursion = 0;
}


void
recursive_lock_init_etc(recursive_lock *lock, const char *name, uint32 flags)
{
	mutex_init_etc(&lock->lock, name != NULL ? name : "recursive lock", flags);
	RECURSIVE_LOCK_HOLDER(lock) = -1;
	lock->recursion = 0;
}


void
recursive_lock_destroy(recursive_lock *lock)
{
	if (lock == NULL)
		return;

	mutex_destroy(&lock->lock);
}


status_t
recursive_lock_lock(recursive_lock *lock)
{
	thread_id thread = thread_get_current_thread_id();

	if (!kernel_startup && !are_interrupts_enabled())
		panic("recursive_lock_lock: called with interrupts disabled for lock "
			"%p (\"%s\")\n", lock, lock->lock.name);

	if (thread != RECURSIVE_LOCK_HOLDER(lock)) {
		mutex_lock(&lock->lock);
#ifndef KDEBUG
		lock->holder = thread;
#endif
	}

	lock->recursion++;
	return B_OK;
}


void
recursive_lock_unlock(recursive_lock *lock)
{
	if (thread_get_current_thread_id() != RECURSIVE_LOCK_HOLDER(lock))
		panic("recursive_lock %p unlocked by non-holder thread!\n", lock);

	if (--lock->recursion == 0) {
#ifndef KDEBUG
		lock->holder = -1;
#endif
		mutex_unlock(&lock->lock);
	}
}


//	#pragma mark -


static status_t
rw_lock_wait(rw_lock* lock, bool writer)
{
	// enqueue in waiter list
	rw_lock_waiter waiter;
	waiter.thread = thread_get_current_thread();
	waiter.next = NULL;
	waiter.writer = writer;

	if (lock->waiters != NULL)
		lock->waiters->last->next = &waiter;
	else
		lock->waiters = &waiter;

	lock->waiters->last = &waiter;

	// block
	thread_prepare_to_block(waiter.thread, 0, THREAD_BLOCK_TYPE_MUTEX, lock);
	return thread_block_locked(waiter.thread);
}


static void
rw_lock_unblock(rw_lock* lock)
{
	// Check whether there any waiting threads at all and whether anyone
	// has the write lock.
	rw_lock_waiter* waiter = lock->waiters;
	if (waiter == NULL || lock->holder > 0)
		return;

	// writer at head of queue?
	if (waiter->writer) {
		if (lock->reader_count == 0) {
			// dequeue writer
			lock->waiters = waiter->next;
			if (lock->waiters != NULL)
				lock->waiters->last = waiter->last;

			lock->holder = waiter->thread->id;
	
			// unblock thread
			thread_unblock_locked(waiter->thread, B_OK);
		}
		return;
	}

	// wake up one or more readers
	while ((waiter = lock->waiters) != NULL && !waiter->writer) {
		// dequeue reader
		lock->waiters = waiter->next;
		if (lock->waiters != NULL)
			lock->waiters->last = waiter->last;

		lock->reader_count++;

		// unblock thread
		thread_unblock_locked(waiter->thread, B_OK);
	}
}


void
rw_lock_init(rw_lock* lock, const char* name)
{
	lock->name = name;
	lock->waiters = NULL;
	lock->holder = -1;
	lock->reader_count = 0;
	lock->writer_count = 0;
	lock->flags = 0;
}


void
rw_lock_init_etc(rw_lock* lock, const char* name, uint32 flags)
{
	lock->name = (flags & RW_LOCK_FLAG_CLONE_NAME) != 0 ? strdup(name) : name;
	lock->waiters = NULL;
	lock->holder = -1;
	lock->reader_count = 0;
	lock->writer_count = 0;
	lock->flags = flags & RW_LOCK_FLAG_CLONE_NAME;
}


void
rw_lock_destroy(rw_lock* lock)
{
	char* name = (lock->flags & RW_LOCK_FLAG_CLONE_NAME) != 0
		? (char*)lock->name : NULL;

	// unblock all waiters
	InterruptsSpinLocker locker(thread_spinlock);

#ifdef KDEBUG
	if (lock->waiters != NULL && thread_get_current_thread_id()
		!= lock->holder) {
		panic("rw_lock_destroy(): there are blocking threads, but the caller "
			"doesn't hold the write lock (%p)", lock);

		locker.Unlock();
		if (rw_lock_write_lock(lock) != B_OK)
			return;
		locker.Lock();
	}
#endif

	while (rw_lock_waiter* waiter = lock->waiters) {
		// dequeue
		lock->waiters = waiter->next;

		// unblock thread
		thread_unblock_locked(waiter->thread, B_ERROR);
	}

	lock->name = NULL;

	locker.Unlock();

	free(name);
}


status_t
rw_lock_read_lock(rw_lock* lock)
{
	InterruptsSpinLocker locker(thread_spinlock);

	if (lock->writer_count == 0) {
		lock->reader_count++;
		return B_OK;
	}

	return rw_lock_wait(lock, false);
}


status_t
rw_lock_read_unlock(rw_lock* lock)
{
	InterruptsSpinLocker locker(thread_spinlock);

	if (lock->reader_count <= 0) {
		panic("rw_lock_read_unlock(): lock %p not read-locked", lock);
		return B_BAD_VALUE;
	}

	lock->reader_count--;

	rw_lock_unblock(lock);

	return B_OK;
}


status_t
rw_lock_write_lock(rw_lock* lock)
{
	InterruptsSpinLocker locker(thread_spinlock);

	if (lock->reader_count == 0 && lock->writer_count == 0) {
		lock->writer_count++;
		lock->holder = thread_get_current_thread_id();
		return B_OK;
	}

	lock->writer_count++;
	return rw_lock_wait(lock, true);
}


status_t
rw_lock_write_unlock(rw_lock* lock)
{
	InterruptsSpinLocker locker(thread_spinlock);

	if (thread_get_current_thread_id() != lock->holder) {
		panic("rw_lock_write_unlock(): lock %p not write-locked by this thread",
			lock);
		return B_BAD_VALUE;
	}

	lock->writer_count--;
	lock->holder = -1;

	rw_lock_unblock(lock);

	return B_OK;
}


// #pragma mark -


void
mutex_init(mutex* lock, const char *name)
{
	lock->name = name;
	lock->waiters = NULL;
#ifdef KDEBUG
	lock->holder = -1;
#else
	lock->count = 0;
#endif
	lock->flags = 0;
}


void
mutex_init_etc(mutex* lock, const char *name, uint32 flags)
{
	lock->name = (flags & MUTEX_FLAG_CLONE_NAME) != 0 ? strdup(name) : name;
	lock->waiters = NULL;
#ifdef KDEBUG
	lock->holder = -1;
#else
	lock->count = 0;
#endif
	lock->flags = flags & MUTEX_FLAG_CLONE_NAME;
}


void
mutex_destroy(mutex* lock)
{
	char* name = (lock->flags & MUTEX_FLAG_CLONE_NAME) != 0
		? (char*)lock->name : NULL;

	// unblock all waiters
	InterruptsSpinLocker locker(thread_spinlock);

#ifdef KDEBUG
	if (lock->waiters != NULL && thread_get_current_thread_id()
		!= lock->holder) {
		panic("mutex_destroy(): there are blocking threads, but caller doesn't "
			"hold the lock (%p)", lock);
		if (_mutex_lock(lock, true) != B_OK)
			return;
	}
#endif

	while (mutex_waiter* waiter = lock->waiters) {
		// dequeue
		lock->waiters = waiter->next;

		// unblock thread
		thread_unblock_locked(waiter->thread, B_ERROR);
	}

	lock->name = NULL;

	locker.Unlock();

	free(name);
}


status_t
_mutex_lock(mutex* lock, bool threadsLocked)
{
#ifdef KDEBUG
	if (!kernel_startup && !threadsLocked && !are_interrupts_enabled()) {
		panic("_mutex_unlock(): called with interrupts disabled for lock %p",
			lock);
	}
#endif

	// lock only, if !threadsLocked
	InterruptsSpinLocker locker(thread_spinlock, false, !threadsLocked);

	// Might have been released after we decremented the count, but before
	// we acquired the spinlock.
#ifdef KDEBUG
	if (lock->holder <= 0) {
		lock->holder = thread_get_current_thread_id();
		return B_OK;
	}
#else
	if ((lock->flags & MUTEX_FLAG_RELEASED) != 0) {
		lock->flags &= ~MUTEX_FLAG_RELEASED;
		return B_OK;
	}
#endif

	// enqueue in waiter list
	mutex_waiter waiter;
	waiter.thread = thread_get_current_thread();
	waiter.next = NULL;

	if (lock->waiters != NULL) {
		lock->waiters->last->next = &waiter;
	} else
		lock->waiters = &waiter;

	lock->waiters->last = &waiter;

	// block
	thread_prepare_to_block(waiter.thread, 0, THREAD_BLOCK_TYPE_MUTEX, lock);
	status_t error = thread_block_locked(waiter.thread);

#ifdef KDEBUG
	if (error == B_OK)
		lock->holder = waiter.thread->id;
#endif

	return error;
}


void
_mutex_unlock(mutex* lock)
{
	InterruptsSpinLocker _(thread_spinlock);

#ifdef KDEBUG
	if (thread_get_current_thread_id() != lock->holder) {
		panic("_mutex_unlock() failure: thread %ld is trying to release "
			"mutex %p (current holder %ld)\n", thread_get_current_thread_id(),
			lock, lock->holder);
		return;
	}
#endif

	mutex_waiter* waiter = lock->waiters;
	if (waiter != NULL) {
		// dequeue the first waiter
		lock->waiters = waiter->next;
		if (lock->waiters != NULL)
			lock->waiters->last = waiter->last;

		// unblock thread
		thread_unblock_locked(waiter->thread, B_OK);

#ifdef KDEBUG
		// Already set the holder to the unblocked thread. Besides that this
		// actually reflects the current situation, setting it to -1 would
		// cause a race condition, since another locker could think the lock
		// is not held by anyone.
		lock->holder = waiter->thread->id;
#endif
	} else {
		// We've acquired the spinlock before the locker that is going to wait.
		// Just mark the lock as released.
#ifdef KDEBUG
		lock->holder = -1;
#else
		lock->flags |= MUTEX_FLAG_RELEASED;
#endif
	}
}


status_t
_mutex_trylock(mutex* lock)
{
#ifdef KDEBUG
	InterruptsSpinLocker _(thread_spinlock);

	if (lock->holder <= 0) {
		lock->holder = thread_get_current_thread_id();
		return B_OK;
	}
#endif
	return B_WOULD_BLOCK;
}


static int
dump_mutex_info(int argc, char** argv)
{
	if (argc < 2) {
		print_debugger_command_usage(argv[0]);
		return 0;
	}

	mutex* lock = (mutex*)strtoul(argv[1], NULL, 0);

	if (!IS_KERNEL_ADDRESS(lock)) {
		kprintf("invalid address: %p\n", lock);
		return 0;
	}

	kprintf("mutex %p:\n", lock);
	kprintf("  name:            %s\n", lock->name);
	kprintf("  flags:           0x%x\n", lock->flags);
#ifdef KDEBUG
	kprintf("  holder:          %ld\n", lock->holder);
#else
	kprintf("  count:           %ld\n", lock->count);
#endif

	kprintf("  waiting threads:");
	mutex_waiter* waiter = lock->waiters;
	while (waiter != NULL) {
		kprintf(" %ld", waiter->thread->id);
		waiter = waiter->next;
	}
	kputs("\n");

	return 0;
}


// #pragma mark -


void
lock_debug_init()
{
	add_debugger_command_etc("mutex", &dump_mutex_info,
		"Dump info about a mutex",
		"<mutex>\n"
		"Prints info about the specified mutex.\n"
		"  <mutex>  - pointer to the mutex to print the info for.\n", 0);
}