/**
* Delivers up an unassigned heavy-weight lock. Locks are allocated from processor specific
* regions or lists, so normally no synchronization is required to obtain a lock.
*
* <p>Collector threads cannot use heavy-weight locks.
*
* @return a free Lock; or <code>null</code>, if garbage collection is not enabled
*/
@UnpreemptibleNoWarn("The caller is prepared to lose control when it allocates a lock")
static Lock allocate() {
RVMThread me = RVMThread.getCurrentThread();
if (me.cachedFreeLock != null) {
Lock l = me.cachedFreeLock;
me.cachedFreeLock = null;
if (trace) {
VM.sysWriteln(
"Lock.allocate: returning ", Magic.objectAsAddress(l),
", a cached free lock from Thread #", me.getThreadSlot());
}
return l;
}
Lock l = null;
while (l == null) {
if (globalFreeLock != null) {
lockAllocationMutex.lock();
l = globalFreeLock;
if (l != null) {
globalFreeLock = l.nextFreeLock;
l.nextFreeLock = null;
l.active = true;
globalFreeLocks--;
}
lockAllocationMutex.unlock();
if (trace && l != null) {
VM.sysWriteln(
"Lock.allocate: returning ", Magic.objectAsAddress(l),
" from the global freelist for Thread #", me.getThreadSlot());
}
} else {
l = new Lock(); // may cause thread switch (and processor loss)
lockAllocationMutex.lock();
if (globalFreeLock == null) {
// ok, it's still correct for us to be adding a new lock
if (nextLockIndex >= MAX_LOCKS) {
VM.sysWriteln("Too many fat locks"); // make MAX_LOCKS bigger? we can keep going??
VM.sysFail("Exiting VM with fatal error");
}
l.index = nextLockIndex++;
globalLocksAllocated++;
} else {
l = null; // someone added to the freelist, try again
}
lockAllocationMutex.unlock();
if (l != null) {
if (l.index >= numLocks()) {
/* We need to grow the table */
growLocks(l.index);
}
addLock(l);
l.active = true;
/* make sure other processors see lock initialization.
* Note: Derek and I BELIEVE that an isync is not required in the other processor because the lock is newly allocated - Bowen */
Magic.sync();
}
if (trace && l != null) {
VM.sysWriteln(
"Lock.allocate: returning ",
Magic.objectAsAddress(l),
", a freshly allocated lock for Thread #",
me.getThreadSlot());
}
}
}
return l;
}
