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, 12 insertions, 0 deletions

diff --git a/includes/FileLock.h b/includes/FileLock.h
new file mode 100644
index 0000000000..3fc1a81aec
--- /dev/null
+++ b/includes/FileLock.h
@@ -0,0 +1,12 @@
+/* -----------------------------------------------------------------------------
+ *
+ * (c) The GHC Team, 2007
+ *
+ * File locking support as required by Haskell 98
+ *
+ * ---------------------------------------------------------------------------*/
+
+void initFileLocking(void);
+void freeFileLocking(void);
+int  lockFile(int fd, dev_t dev, ino_t ino, int for_writing);
+int  unlockFile(int fd);