Implement -XStaticValues.wip/static-pointers

Contains contributions from Alexander Vershilov and Mathieu Boespflug.

As proposed in [1], this extension introduces a new syntactic form
`static e`, where `e :: a` can be any closed expression. The static form
produces a value of type `StaticPtr a`, which works as a reference that
programs can "dereference" to get the value of `e` back. References are
like `Ptr`s, except that they are stable across invocations of a
program.

In essence the extension collects the arguments of the static form into
a global static pointer table. The expressions can be looked up by a
fingerprint computed from the package, the module and a fresh name
given to the expression. For more details we refer to the users guide
section contained in the patch.

The extension is a contribution to the Cloud Haskell ecosystem
(distributed-process and related), and thus has the potential to foster
Haskell as a programming language for distributed systems.

The immediate improvement brought by the extension is the elimination of
remote tables from Cloud Haskell applications. Such applications contain
table fragments spread throughout multiple modules and packages.
Eliminating these fragments saves the programmer the burden required to
construct and assemble the global remote table, a verbose and
error-prone process, even with the help of Template Haskell, that
moreover pollutes the export lists of all modules.

[1] Jeff Epstein, Andrew P. Black, and Simon Peyton-Jones. Towards
Haskell in the cloud. SIGPLAN Not., 46(12):118–129, September 2011. ISSN
0362-1340.

1 files changed, 41 insertions, 0 deletions

diff --git a/rts/Hash.c b/rts/Hash.c
index b91d70c219..1c167168d2 100644
--- a/rts/Hash.c
+++ b/rts/Hash.c
@@ -16,6 +16,10 @@
 
 #include <string.h>
 
+#ifdef HAVE_UNISTD_H
+#include <unistd.h>
+#endif
+
 #define HSEGSIZE    1024    /* Size of a single hash table segment */
                             /* Also the minimum size of a hash table */
 #define HDIRSIZE    1024    /* Size of the segment directory */
@@ -99,6 +103,31 @@ hashStr(HashTable *table, char *key)
     return bucket;
 }
 
+int
+hashFingerprint(HashTable *table, uint64_t *key)
+{
+    int h, bucket;
+    char *s;
+
+    s = (char *)key;
+    size_t i;
+    for (i=0, h=0; i< sizeof(uint64_t)*2; ++i, ++s) {
+        h *= 128;
+        h += *s;
+        h = h % 1048583;        /* some random large prime */
+    }
+
+    /* Mod the size of the hash table (a power of 2) */
+    bucket = h & table->mask1;
+
+    if (bucket < table->split) {
+        /* Mod the size of the expanded hash table (also a power of 2) */
+        bucket = h & table->mask2;
+    }
+
+    return bucket;
+}
+
 static int
 compareWord(StgWord key1, StgWord key2)
 {
@@ -111,6 +140,11 @@ compareStr(StgWord key1, StgWord key2)
     return (strcmp((char *)key1, (char *)key2) == 0);
 }
 
+static int
+compareFingerprint(uint64_t *ptra, uint64_t *ptrb) {
+    return (ptra[0]-ptrb[0]==0ULL)?((ptra[1] - ptrb[1] == 0ULL)?0:1):1;
+}
+
 
 /* -----------------------------------------------------------------------------
  * Allocate a new segment of the dynamically growing hash table.
@@ -387,6 +421,13 @@ allocStrHashTable(void)
                            (CompareFunction *)compareStr);
 }
 
+HashTable *
+allocFpHashTable(void)
+{
+    return allocHashTable_((HashFunction *)hashFingerprint,
+                           (CompareFunction *)compareFingerprint);
+}
+
 void
 exitHashTable(void)
 {