/**
* @param usedRate must be power of 2 minus 1, and it determines the likelihood that calling the
* used method actually moves the node in the usage list. The higher the used rate value, the
* less likely that calling the used method does anything. The used rate value should be
* proportional to the total cache size. For larger caches, exact MRU ordering is less
* critical, and the cost of updating the ordering is also higher. Hence, a larger used rate
* value is recommended.
*/
NodeUsageList(LocalDatabase db, long usedRate, int maxSize) {
if (maxSize <= 0) {
throw new IllegalArgumentException();
}
mDatabase = db;
mPageSize = db.pageSize();
mUsedRate = usedRate;
acquireExclusive();
mMaxSize = maxSize;
releaseExclusive();
}
/**
* Caller must acquire latch, which is released by this method.
*
* @param arena optional
* @param mode MODE_UNEVICTABLE
*/
private Node doAllocLatchedNode(Object arena, int mode) throws DatabaseException {
try {
mDatabase.checkClosed();
/*P*/ byte[] page;
/*P*/
// [
page = p_calloc(arena, mPageSize);
/*P*/
// |
/*P*/
// page = mDatabase.mFullyMapped ? p_nonTreePage() : p_calloc(arena, mPageSize);
/*P*/
// ]
Node node = new Node(this, page);
node.acquireExclusive();
mSize++;
if ((mode & MODE_UNEVICTABLE) == 0) {
Node most = mMostRecentlyUsed;
node.mLessUsed = most;
if (most == null) {
mLeastRecentlyUsed = node;
} else {
most.mMoreUsed = node;
}
mMostRecentlyUsed = node;
}
// Return with node latch still held.
return node;
} finally {
releaseExclusive();
}
}