Move file locking into the RTS, fixing #629, #1109

File locking (of the Haskell 98 variety) was previously done using a
static table with linear search, which had two problems: the array had
a fixed size and was sometimes too small (#1109), and performance of
lockFile/unlockFile was suboptimal due to the linear search.
Also the algorithm failed to count readers as required by Haskell 98
(#629).

Now it's done using a hash table (provided by the RTS).  Furthermore I
avoided the extra fstat() for every open file by passing the dev_t and
ino_t into lockFile.  This and the improvements to the locking
algorithm result in a healthy 20% or so performance increase for
opening/closing files (see openFile008 test).

1 files changed, 7 insertions, 0 deletions

diff --git a/rts/Hash.h b/rts/Hash.h
index fb83fdfa9e..d16f9ae9c1 100644
--- a/rts/Hash.h
+++ b/rts/Hash.h
@@ -32,6 +32,13 @@ HashTable * allocStrHashTable ( void );
 #define removeStrHashTable(table, key, data) \
    (removeHashTable(table, (StgWord)key, data))
 
+/* Hash tables for arbitrary keys */
+typedef int HashFunction(HashTable *table, StgWord key);
+typedef int CompareFunction(StgWord key1, StgWord key2);
+HashTable * allocHashTable_(HashFunction *hash, CompareFunction *compare);
+int hashWord(HashTable *table, StgWord key);
+int hashStr(HashTable *table, char *key);
+
 /* Freeing hash tables 
  */
 void freeHashTable ( HashTable *table, void (*freeDataFun)(void *) );