haiku-beta6/src/system/kernel/condition_variable.cpp

/*
 * Copyright 2007-2011, Ingo Weinhold, [email protected].
 * Copyright 2019, Haiku, Inc. All rights reserved.
 * Distributed under the terms of the MIT License.
 */

#include <condition_variable.h>

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

#include <debug.h>
#include <kscheduler.h>
#include <ksignal.h>
#include <int.h>
#include <listeners.h>
#include <scheduling_analysis.h>
#include <thread.h>
#include <util/AutoLock.h>
#include <util/atomic.h>


#define STATUS_ADDED	1
#define STATUS_WAITING	2


static const int kConditionVariableHashSize = 512;


struct ConditionVariableHashDefinition {
	typedef const void* KeyType;
	typedef	ConditionVariable ValueType;

	size_t HashKey(const void* key) const
		{ return (size_t)key; }
	size_t Hash(ConditionVariable* variable) const
		{ return (size_t)variable->fObject; }
	bool Compare(const void* key, ConditionVariable* variable) const
		{ return key == variable->fObject; }
	ConditionVariable*& GetLink(ConditionVariable* variable) const
		{ return variable->fNext; }
};

typedef BOpenHashTable<ConditionVariableHashDefinition> ConditionVariableHash;
static ConditionVariableHash sConditionVariableHash;
static rw_spinlock sConditionVariableHashLock;


static int
list_condition_variables(int argc, char** argv)
{
	ConditionVariable::ListAll();
	return 0;
}


static int
dump_condition_variable(int argc, char** argv)
{
	if (argc != 2) {
		print_debugger_command_usage(argv[0]);
		return 0;
	}

	addr_t address = parse_expression(argv[1]);
	if (address == 0)
		return 0;

	ConditionVariable* variable = sConditionVariableHash.Lookup((void*)address);

	if (variable == NULL) {
		// It must be a direct pointer to a condition variable.
		variable = (ConditionVariable*)address;
	}

	if (variable != NULL) {
		variable->Dump();

		set_debug_variable("_cvar", (addr_t)variable);
		set_debug_variable("_object", (addr_t)variable->Object());

	} else
		kprintf("no condition variable at or with key %p\n", (void*)address);

	return 0;
}


// #pragma mark - ConditionVariableEntry


bool
ConditionVariableEntry::Add(const void* object)
{
	ASSERT(object != NULL);

	InterruptsLocker _;
	ReadSpinLocker hashLocker(sConditionVariableHashLock);

	ConditionVariable* variable = sConditionVariableHash.Lookup(object);

	if (variable == NULL) {
		fWaitStatus = B_ENTRY_NOT_FOUND;
		return false;
	}

	SpinLocker variableLocker(variable->fLock);
	hashLocker.Unlock();

	AddToLockedVariable(variable);

	return true;
}


inline void
ConditionVariableEntry::AddToLockedVariable(ConditionVariable* variable)
{
	ASSERT(fVariable == NULL);

	B_INITIALIZE_SPINLOCK(&fLock);
	fThread = thread_get_current_thread();
	fVariable = variable;
	fWaitStatus = STATUS_ADDED;
	fVariable->fEntries.Add(this);
}


status_t
ConditionVariableEntry::Wait(uint32 flags, bigtime_t timeout)
{
#if KDEBUG
	if (!are_interrupts_enabled()) {
		panic("ConditionVariableEntry::Wait() called with interrupts "
			"disabled, entry: %p, variable: %p", this, fVariable);
		return B_ERROR;
	}
#endif

	InterruptsLocker _;
	SpinLocker entryLocker(fLock);

	if (fVariable == NULL)
		return fWaitStatus;

	thread_prepare_to_block(fThread, flags,
		THREAD_BLOCK_TYPE_CONDITION_VARIABLE, fVariable);

	fWaitStatus = STATUS_WAITING;

	entryLocker.Unlock();

	status_t error;
	if ((flags & (B_RELATIVE_TIMEOUT | B_ABSOLUTE_TIMEOUT)) != 0)
		error = thread_block_with_timeout(flags, timeout);
	else
		error = thread_block();

	entryLocker.Lock();

	// Remove entry from variable, if not done yet.
	if (fVariable != NULL) {
		SpinLocker conditionLocker(fVariable->fLock);
		if (fVariable->fEntries.Contains(this)) {
			fVariable->fEntries.Remove(this);
		} else {
			entryLocker.Unlock();
			// The variable's fEntries did not contain us, but we currently
			// have the variable's lock acquired. This must mean we are in
			// a race with the variable's Notify. It is possible we will be
			// destroyed immediately upon returning here, so we need to
			// spin until our fVariable member is unset by the Notify thread
			// and then re-acquire our own lock to avoid a use-after-free.
			while (atomic_pointer_get(&fVariable) != NULL) {}
			entryLocker.Lock();
		}
		fVariable = NULL;
	}

	return error;
}


status_t
ConditionVariableEntry::Wait(const void* object, uint32 flags,
	bigtime_t timeout)
{
	if (Add(object))
		return Wait(flags, timeout);
	return B_ENTRY_NOT_FOUND;
}


// #pragma mark - ConditionVariable


/*!	Initialization method for anonymous (unpublished) condition variables.
*/
void
ConditionVariable::Init(const void* object, const char* objectType)
{
	fObject = object;
	fObjectType = objectType;
	new(&fEntries) EntryList;
	B_INITIALIZE_SPINLOCK(&fLock);

	T_SCHEDULING_ANALYSIS(InitConditionVariable(this, object, objectType));
	NotifyWaitObjectListeners(&WaitObjectListener::ConditionVariableInitialized,
		this);
}


void
ConditionVariable::Publish(const void* object, const char* objectType)
{
	ASSERT(object != NULL);

	fObject = object;
	fObjectType = objectType;
	new(&fEntries) EntryList;
	B_INITIALIZE_SPINLOCK(&fLock);

	T_SCHEDULING_ANALYSIS(InitConditionVariable(this, object, objectType));
	NotifyWaitObjectListeners(&WaitObjectListener::ConditionVariableInitialized,
		this);

	InterruptsWriteSpinLocker _(sConditionVariableHashLock);

	ASSERT_PRINT(sConditionVariableHash.Lookup(object) == NULL,
		"condition variable: %p\n", sConditionVariableHash.Lookup(object));

	sConditionVariableHash.InsertUnchecked(this);
}


void
ConditionVariable::Unpublish()
{
	ASSERT(fObject != NULL);

	InterruptsLocker _;
	WriteSpinLocker hashLocker(sConditionVariableHashLock);
	SpinLocker selfLocker(fLock);

#if KDEBUG
	ConditionVariable* variable = sConditionVariableHash.Lookup(fObject);
	if (variable != this) {
		panic("Condition variable %p not published, found: %p", this, variable);
		return;
	}
#endif

	sConditionVariableHash.RemoveUnchecked(this);
	fObject = NULL;
	fObjectType = NULL;

	hashLocker.Unlock();

	if (!fEntries.IsEmpty())
		_NotifyLocked(true, B_ENTRY_NOT_FOUND);
}


void
ConditionVariable::Add(ConditionVariableEntry* entry)
{
	InterruptsSpinLocker _(fLock);
	entry->AddToLockedVariable(this);
}


status_t
ConditionVariable::Wait(uint32 flags, bigtime_t timeout)
{
	ConditionVariableEntry entry;
	Add(&entry);
	return entry.Wait(flags, timeout);
}


/*static*/ void
ConditionVariable::NotifyOne(const void* object, status_t result)
{
	InterruptsReadSpinLocker locker(sConditionVariableHashLock);
	ConditionVariable* variable = sConditionVariableHash.Lookup(object);
	locker.Unlock();
	if (variable == NULL)
		return;

	variable->NotifyOne(result);
}


/*static*/ void
ConditionVariable::NotifyAll(const void* object, status_t result)
{
	InterruptsReadSpinLocker locker(sConditionVariableHashLock);
	ConditionVariable* variable = sConditionVariableHash.Lookup(object);
	locker.Unlock();
	if (variable == NULL)
		return;

	variable->NotifyAll(result);
}


void
ConditionVariable::_Notify(bool all, status_t result)
{
	InterruptsSpinLocker _(fLock);

	if (!fEntries.IsEmpty()) {
		if (result > B_OK) {
			panic("tried to notify with invalid result %" B_PRId32 "\n", result);
			result = B_ERROR;
		}

		_NotifyLocked(all, result);
	}
}


/*! Called with interrupts disabled and the condition variable's spinlock held.
 */
void
ConditionVariable::_NotifyLocked(bool all, status_t result)
{
	// Dequeue and wake up the blocked threads.
	// We *cannot* hold our own lock while acquiring the Entry's lock,
	// as this leads to a (non-theoretical!) race between the Entry
	// entering Wait() and acquiring its own lock, and then acquiring ours.
	while (ConditionVariableEntry* entry = fEntries.RemoveHead()) {
		release_spinlock(&fLock);
		acquire_spinlock(&entry->fLock);

		entry->fVariable = NULL;

		if (entry->fWaitStatus <= 0) {
			release_spinlock(&entry->fLock);
			acquire_spinlock(&fLock);
			continue;
		}

		if (entry->fWaitStatus == STATUS_WAITING) {
			SpinLocker _(entry->fThread->scheduler_lock);
			thread_unblock_locked(entry->fThread, result);
		}

		entry->fWaitStatus = result;

		release_spinlock(&entry->fLock);
		acquire_spinlock(&fLock);

		if (!all)
			break;
	}
}


/*static*/ void
ConditionVariable::ListAll()
{
	kprintf("  variable      object (type)                waiting threads\n");
	kprintf("------------------------------------------------------------\n");
	ConditionVariableHash::Iterator it(&sConditionVariableHash);
	while (ConditionVariable* variable = it.Next()) {
		// count waiting threads
		int count = variable->fEntries.Count();

		kprintf("%p  %p  %-20s %15d\n", variable, variable->fObject,
			variable->fObjectType, count);
	}
}


void
ConditionVariable::Dump() const
{
	kprintf("condition variable %p\n", this);
	kprintf("  object:  %p (%s)\n", fObject, fObjectType);
	kprintf("  threads:");

	for (EntryList::ConstIterator it = fEntries.GetIterator();
		 ConditionVariableEntry* entry = it.Next();) {
		kprintf(" %" B_PRId32, entry->fThread->id);
	}
	kprintf("\n");
}


// #pragma mark -


void
condition_variable_init()
{
	new(&sConditionVariableHash) ConditionVariableHash;

	status_t error = sConditionVariableHash.Init(kConditionVariableHashSize);
	if (error != B_OK) {
		panic("condition_variable_init(): Failed to init hash table: %s",
			strerror(error));
	}

	add_debugger_command_etc("cvar", &dump_condition_variable,
		"Dump condition variable info",
		"<address>\n"
		"Prints info for the specified condition variable.\n"
		"  <address>  - Address of the condition variable or the object it is\n"
		"               associated with.\n", 0);
	add_debugger_command_etc("cvars", &list_condition_variables,
		"List condition variables",
		"\n"
		"Lists all existing condition variables\n", 0);
}