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DfsBlockCache.hasBlock0: quickly check for file in cache 

This can be useful for sophisticated pre-read algorithms to quickly
determine if a file is likely already in cache, especially small
reftables which may be smaller than a typical DFS block size.

Change-Id: I7756948063b722ff650c9ba82060ff9ad554b0ba
This commit is contained in:
Shawn Pearce 2017-12-13 17:10:51 -08:00
parent c09ed93e85
commit f635aa51f8
1 changed files with 17 additions and 0 deletions
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17
org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/dfs/DfsBlockCache.java
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@ -279,6 +279,23 @@ public long[] getEvictions() {
return getStatVals(statEvict);
}
/**
* Quickly check if the cache contains block 0 of the given stream.
* <p>
* This can be useful for sophisticated pre-read algorithms to quickly
* determine if a file is likely already in cache, especially small
* reftables which may be smaller than a typical DFS block size.
*
* @param key
* the file to check.
* @return true if block 0 (the first block) is in the cache.
*/
public boolean hasBlock0(DfsStreamKey key) {
HashEntry e1 = table.get(slot(key, 0));
DfsBlock v = scan(e1, key, 0);
return v != null && v.contains(key, 0);
}
private int hash(int packHash, long off) {
return packHash + (int) (off >>> blockSizeShift);
}