Implement -XStaticValues

Summary:
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.

The relevant wiki pages are [2, 3], which describe the motivation/ideas
and implementation plan respectively.

[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.
[2] https://ghc.haskell.org/trac/ghc/wiki/StaticPointers
[3] https://ghc.haskell.org/trac/ghc/wiki/StaticPointers/ImplementationPlan

Authored-by: Facundo Domínguez <facundo.dominguez@tweag.io>
Authored-by: Mathieu Boespflug <m@tweag.io>
Authored-by: Alexander Vershilov <alexander.vershilov@tweag.io>

Test Plan: `./validate`

Reviewers: hvr, simonmar, simonpj, austin

Reviewed By: simonpj, austin

Subscribers: qnikst, bgamari, mboes, carter, thomie, goldfire

Differential Revision: https://phabricator.haskell.org/D550

GHC Trac Issues: #7015

1 files changed, 57 insertions, 0 deletions

diff --git a/rts/StaticPtrTable.c b/rts/StaticPtrTable.c
new file mode 100644
index 0000000000..bd450809d0
--- /dev/null
+++ b/rts/StaticPtrTable.c
@@ -0,0 +1,57 @@
+/*
+ * (c)2014 Tweag I/O
+ *
+ * The Static Pointer Table implementation.
+ *
+ * https://ghc.haskell.org/trac/ghc/wiki/StaticPointers
+ * https://ghc.haskell.org/trac/ghc/wiki/StaticPointers/ImplementationPlan
+ *
+ */
+
+#include "Rts.h"
+#include "StaticPtrTable.h"
+#include "Hash.h"
+
+static HashTable * spt = NULL;
+
+/// Hash function for the SPT.
+static int hashFingerprint(HashTable *table, StgWord64 key[2]) {
+  // Take half of the key to compute the hash.
+  return hashWord(table, (StgWord)key[1]);
+}
+
+/// Comparison function for the SPT.
+static int compareFingerprint(StgWord64 ptra[2], StgWord64 ptrb[2]) {
+  return ptra[0] == ptrb[0] && ptra[1] == ptrb[1];
+}
+
+void hs_spt_insert(StgWord64 key[2],void *spe_closure) {
+  // hs_spt_insert is called from constructor functions, so
+  // the SPT needs to be initialized here.
+  if (spt == NULL)
+    spt = allocHashTable_( (HashFunction *)hashFingerprint
+                         , (CompareFunction *)compareFingerprint
+                         );
+
+  getStablePtr(spe_closure);
+  insertHashTable(spt, (StgWord)key, spe_closure);
+}
+
+StgPtr hs_spt_lookup(StgWord64 key[2]) {
+  return spt ? lookupHashTable(spt, (StgWord)key) : NULL;
+}
+
+int hs_spt_keys(StgPtr keys[], int szKeys) {
+  return spt ? keysHashTable(spt, (StgWord*)keys, szKeys) : 0;
+}
+
+int hs_spt_key_count() {
+  return spt ? keyCountHashTable(spt) : 0;
+}
+
+void exitStaticPtrTable() {
+  if (spt) {
+    freeHashTable(spt, NULL);
+    spt = NULL;
+  }
+}