Finish stable split

Long ago, the stable name table and stable pointer tables were one.
Now, they are separate, and have significantly different
implementations. I believe the time has come to finish the split
that began in #7674.

* Divide `rts/Stable` into `rts/StableName` and `rts/StablePtr`.

* Give each table its own mutex.

* Add FFI functions `hs_lock_stable_ptr_table` and
`hs_unlock_stable_ptr_table` and document them.
  These are intended to replace the previously undocumented
`hs_lock_stable_tables` and `hs_lock_stable_tables`,
  which are now documented as deprecated synonyms.

* Make `eqStableName#` use pointer equality instead of unnecessarily
comparing stable name table indices.

Reviewers: simonmar, bgamari, erikd

Reviewed By: bgamari

Subscribers: rwbarton, carter

GHC Trac Issues: #15555

Differential Revision: https://phabricator.haskell.org/D5084

2 files changed, 20 insertions, 11 deletions

diff --git a/rts/sm/Compact.c b/rts/sm/Compact.c
index 10ad73c7d7..004e042069 100644
--- a/rts/sm/Compact.c
+++ b/rts/sm/Compact.c
@@ -25,7 +25,8 @@
 #include "Trace.h"
 #include "Weak.h"
 #include "MarkWeak.h"
-#include "Stable.h"
+#include "StablePtr.h"
+#include "StableName.h"
 
 // Turn off inlining when debugging - it obfuscates things
 #if defined(DEBUG)
@@ -1000,7 +1001,10 @@ compact(StgClosure *static_objects)
     thread_static(static_objects /* ToDo: ok? */);
 
     // the stable pointer table
-    threadStableTables((evac_fn)thread_root, NULL);
+    threadStablePtrTable((evac_fn)thread_root, NULL);
+
+    // the stable name table
+    threadStableNameTable((evac_fn)thread_root, NULL);
 
     // the CAF list (used by GHCi)
     markCAFs((evac_fn)thread_root, NULL);
diff --git a/rts/sm/GC.c b/rts/sm/GC.c
index 90857abe38..70d6d8efe5 100644
--- a/rts/sm/GC.c
+++ b/rts/sm/GC.c
@@ -46,7 +46,8 @@
 #include "RetainerProfile.h"
 #include "LdvProfile.h"
 #include "RaiseAsync.h"
-#include "Stable.h"
+#include "StableName.h"
+#include "StablePtr.h"
 #include "CheckUnload.h"
 #include "CNF.h"
 #include "RtsFlags.h"
@@ -238,8 +239,9 @@ GarbageCollect (uint32_t collect_gen,
   // tell the stats department that we've started a GC
   stat_startGC(cap, gct);
 
-  // lock the StablePtr table
-  stableLock();
+  // Lock the StablePtr table. This prevents FFI calls manipulating
+  // the table from occurring during GC.
+  stablePtrLock();
 
 #if defined(DEBUG)
   mutlist_MUTVARS = 0;
@@ -405,7 +407,10 @@ GarbageCollect (uint32_t collect_gen,
   initWeakForGC();
 
   // Mark the stable pointer table.
-  markStableTables(mark_root, gct);
+  markStablePtrTable(mark_root, gct);
+
+  // Remember old stable name addresses.
+  rememberOldStableNameAddresses ();
 
   /* -------------------------------------------------------------------------
    * Repeatedly scavenge all the areas we know about until there's no
@@ -431,7 +436,7 @@ GarbageCollect (uint32_t collect_gen,
   shutdown_gc_threads(gct->thread_index, idle_cap);
 
   // Now see which stable names are still alive.
-  gcStableTables();
+  gcStableNameTable();
 
 #if defined(THREADED_RTS)
   if (n_gc_threads == 1) {
@@ -730,15 +735,15 @@ GarbageCollect (uint32_t collect_gen,
   if (major_gc) { gcCAFs(); }
 #endif
 
-  // Update the stable pointer hash table.
-  updateStableTables(major_gc);
+  // Update the stable name hash table
+  updateStableNameTable(major_gc);
 
   // unlock the StablePtr table.  Must be before scheduleFinalizers(),
   // because a finalizer may call hs_free_fun_ptr() or
   // hs_free_stable_ptr(), both of which access the StablePtr table.
-  stableUnlock();
+  stablePtrUnlock();
 
-  // Must be after stableUnlock(), because it might free stable ptrs.
+  // Must be after stablePtrUnlock(), because it might free stable ptrs.
   if (major_gc) {
       checkUnload (gct->scavenged_static_objects);
   }