/** RaceDet: get recursion count, assuming lock is held by current thread */
@Uninterruptible
@NoNullCheck
@Inline
public static final int getRecursionCountLocked(Object o, Offset lockOffset) {
if (VM.VerifyAssertions) {
VM._assert(holdsLock(o, lockOffset, RVMThread.getCurrentThread()));
}
Word bits = Magic.getWordAtOffset(o, lockOffset);
int count;
if (bits.and(TL_STAT_MASK).EQ(TL_STAT_FAT)) {
// if locked, then it is locked with a fat lock
Lock l = Lock.getLock(getLockIndex(bits));
l.mutex.lock();
count = l.getRecursionCount();
l.mutex.unlock();
} else {
if (VM.VerifyAssertions) {
VM._assert(
bits.and(TL_STAT_MASK).EQ(TL_STAT_BIASABLE) || bits.and(TL_STAT_MASK).EQ(TL_STAT_THIN));
}
count = getRecCount(bits);
}
if (VM.VerifyAssertions) {
VM._assert(count > 0);
}
return count;
}
@Uninterruptible
@NoNullCheck
public static boolean holdsLock(Object o, Offset lockOffset, RVMThread thread) {
for (int cnt = 0; ; ++cnt) {
int tid = thread.getLockingId();
Word bits = Magic.getWordAtOffset(o, lockOffset);
if (bits.and(TL_STAT_MASK).EQ(TL_STAT_BIASABLE)) {
// if locked, then it is locked with a thin lock
return bits.and(TL_THREAD_ID_MASK).toInt() == tid && !bits.and(TL_LOCK_COUNT_MASK).isZero();
} else if (bits.and(TL_STAT_MASK).EQ(TL_STAT_THIN)) {
return bits.and(TL_THREAD_ID_MASK).toInt() == tid;
} else {
if (VM.VerifyAssertions) VM._assert(bits.and(TL_STAT_MASK).EQ(TL_STAT_FAT));
// if locked, then it is locked with a fat lock
Lock l = Lock.getLock(getLockIndex(bits));
if (l != null) {
l.mutex.lock();
boolean result = (l.getOwnerId() == tid && l.getLockedObject() == o);
l.mutex.unlock();
return result;
}
}
RVMThread.yield();
}
}
/**
* Obtains the heavy-weight lock, if there is one, associated with the indicated object. Returns
* <code>null</code>, if there is no heavy-weight lock associated with the object.
*
* @param o the object from which a lock is desired
* @param lockOffset the offset of the thin lock word in the object.
* @param create if true, create heavy lock if none found
* @return the heavy-weight lock on the object (if any)
*/
@Unpreemptible
public static Lock getHeavyLock(Object o, Offset lockOffset, boolean create) {
Word old = Magic.getWordAtOffset(o, lockOffset);
if (isFat(old)) { // already a fat lock in place
return Lock.getLock(getLockIndex(old));
} else if (create) {
return inflate(o, lockOffset);
} else {
return null;
}
}
@NoInline
@NoNullCheck
@Unpreemptible
public static void unlock(Object o, Offset lockOffset) {
Word threadId = Word.fromIntZeroExtend(RVMThread.getCurrentThread().getLockingId());
for (int cnt = 0; ; cnt++) {
Word old = Magic.getWordAtOffset(o, lockOffset);
Word stat = old.and(TL_STAT_MASK);
if (stat.EQ(TL_STAT_BIASABLE)) {
Word id = old.and(TL_THREAD_ID_MASK);
if (id.EQ(threadId)) {
if (old.and(TL_LOCK_COUNT_MASK).isZero()) {
RVMThread.raiseIllegalMonitorStateException(
"biased unlocking: we own this object but the count is already zero", o);
}
setDedicatedU16(o, lockOffset, old.minus(TL_LOCK_COUNT_UNIT));
return;
} else {
RVMThread.raiseIllegalMonitorStateException(
"biased unlocking: we don't own this object", o);
}
} else if (stat.EQ(TL_STAT_THIN)) {
Magic.sync();
Word id = old.and(TL_THREAD_ID_MASK);
if (id.EQ(threadId)) {
Word changed;
if (old.and(TL_LOCK_COUNT_MASK).isZero()) {
changed = old.and(TL_UNLOCK_MASK).or(TL_STAT_THIN);
} else {
changed = old.minus(TL_LOCK_COUNT_UNIT);
}
if (Synchronization.tryCompareAndSwap(o, lockOffset, old, changed)) {
return;
}
} else {
if (false) {
VM.sysWriteln("threadId = ", threadId);
VM.sysWriteln("id = ", id);
}
RVMThread.raiseIllegalMonitorStateException(
"thin unlocking: we don't own this object", o);
}
} else {
if (VM.VerifyAssertions) VM._assert(stat.EQ(TL_STAT_FAT));
// fat unlock
Lock.getLock(getLockIndex(old)).unlockHeavy(o);
return;
}
}
}
/**
* Promotes a light-weight lock to a heavy-weight lock. If this returns the lock that you gave it,
* its mutex will be locked; otherwise, its mutex will be unlocked. Hence, calls to this method
* should always be followed by a condition lock() or unlock() call.
*
* @param o the object to get a heavy-weight lock
* @param lockOffset the offset of the thin lock word in the object.
* @return the inflated lock; either the one you gave, or another one, if the lock was inflated by
* some other thread.
*/
@NoNullCheck
@Unpreemptible
protected static Lock attemptToInflate(Object o, Offset lockOffset, Lock l) {
if (false) VM.sysWriteln("l = ", Magic.objectAsAddress(l));
l.mutex.lock();
for (int cnt = 0; ; ++cnt) {
Word bits = Magic.getWordAtOffset(o, lockOffset);
// check to see if another thread has already created a fat lock
if (isFat(bits)) {
if (trace) {
VM.sysWriteln(
"Thread #",
RVMThread.getCurrentThreadSlot(),
": freeing lock ",
Magic.objectAsAddress(l),
" because we had a double-inflate");
}
Lock result = Lock.getLock(getLockIndex(bits));
if (result == null || result.lockedObject != o) {
continue; /* this is nasty. this will happen when a lock
is deflated. */
}
Lock.free(l);
l.mutex.unlock();
return result;
}
if (VM.VerifyAssertions) VM._assert(l != null);
if (attemptToMarkInflated(o, lockOffset, bits, l.index, cnt)) {
l.setLockedObject(o);
l.setOwnerId(getLockOwner(bits));
if (l.getOwnerId() != 0) {
l.setRecursionCount(getRecCount(bits));
} else {
if (VM.VerifyAssertions) VM._assert(l.getRecursionCount() == 0);
}
return l;
}
// contention detected, try again
}
}
@NoInline
@NoNullCheck
@Unpreemptible
public static void lock(Object o, Offset lockOffset) {
if (STATS) fastLocks++;
Word threadId = Word.fromIntZeroExtend(RVMThread.getCurrentThread().getLockingId());
for (int cnt = 0; ; cnt++) {
Word old = Magic.getWordAtOffset(o, lockOffset);
Word stat = old.and(TL_STAT_MASK);
boolean tryToInflate = false;
if (stat.EQ(TL_STAT_BIASABLE)) {
Word id = old.and(TL_THREAD_ID_MASK);
if (id.isZero()) {
if (ENABLE_BIASED_LOCKING) {
// lock is unbiased, bias it in our favor and grab it
if (Synchronization.tryCompareAndSwap(
o, lockOffset, old, old.or(threadId).plus(TL_LOCK_COUNT_UNIT))) {
Magic.isync();
return;
}
} else {
// lock is unbiased but biasing is NOT allowed, so turn it into
// a thin lock
if (Synchronization.tryCompareAndSwap(
o, lockOffset, old, old.or(threadId).or(TL_STAT_THIN))) {
Magic.isync();
return;
}
}
} else if (id.EQ(threadId)) {
// lock is biased in our favor
Word changed = old.plus(TL_LOCK_COUNT_UNIT);
if (!changed.and(TL_LOCK_COUNT_MASK).isZero()) {
setDedicatedU16(o, lockOffset, changed);
return;
} else {
tryToInflate = true;
}
} else {
if (casFromBiased(o, lockOffset, old, biasBitsToThinBits(old), cnt)) {
continue; // don't spin, since it's thin now
}
}
} else if (stat.EQ(TL_STAT_THIN)) {
Word id = old.and(TL_THREAD_ID_MASK);
if (id.isZero()) {
if (Synchronization.tryCompareAndSwap(o, lockOffset, old, old.or(threadId))) {
Magic.isync();
return;
}
} else if (id.EQ(threadId)) {
Word changed = old.plus(TL_LOCK_COUNT_UNIT);
if (changed.and(TL_LOCK_COUNT_MASK).isZero()) {
tryToInflate = true;
} else if (Synchronization.tryCompareAndSwap(o, lockOffset, old, changed)) {
Magic.isync();
return;
}
} else if (cnt > retryLimit) {
tryToInflate = true;
}
} else {
if (VM.VerifyAssertions) VM._assert(stat.EQ(TL_STAT_FAT));
// lock is fat. contend on it.
if (Lock.getLock(getLockIndex(old)).lockHeavy(o)) {
return;
}
}
if (tryToInflate) {
if (STATS) slowLocks++;
// the lock is not fat, is owned by someone else, or else the count wrapped.
// attempt to inflate it (this may fail, in which case we'll just harmlessly
// loop around) and lock it (may also fail, if we get the wrong lock). if it
// succeeds, we're done.
// NB: this calls into our attemptToMarkInflated() method, which will do the
// Right Thing if the lock is biased to someone else.
if (inflateAndLock(o, lockOffset)) {
return;
}
} else {
RVMThread.yield();
}
}
}
