Allow refc binaries in literal pools

To simplify the implementation of literal pools (constant pools)
for the R12 release, a shortcut was taken regarding binaries --
all binaries would be stored as heap binaries regardless of size.

To allow a module containing literals to be unloaded, literal
terms are copied when sent to another process. That means that
huge literal binaries will also be copied if they are sent to
another process, which could be surprising.

Another problem is that the arity field in the header for the heap
object may not be wide enough to handle big binaries.

Therefore, bite the bullet and allow refc binaries to be stored
in literal pools. In short, the following need to be changed:

* Each loaded module needs a MSO list, linking all refc binaries
  in the literal pool.

* When check_process_code/2 copies literals to a process heap,
  it must link each referenced binary into the MSO list for the
  process and increment the reference counter for the binary.

* purge_module/1 must decrement the reference counter for each
  refc binary in the literal pool.

1 files changed, 46 insertions, 1 deletions

diff --git a/erts/emulator/beam/erl_gc.c b/erts/emulator/beam/erl_gc.c
index c29352a227..eb2b945877 100644
--- a/erts/emulator/beam/erl_gc.c
+++ b/erts/emulator/beam/erl_gc.c
@@ -595,7 +595,9 @@ erts_garbage_collect_hibernate(Process* p)
 
 
 void
-erts_garbage_collect_literals(Process* p, Eterm* literals, Uint lit_size)
+erts_garbage_collect_literals(Process* p, Eterm* literals,
+			      Uint lit_size,
+			      struct erl_off_heap_header* oh)
 {
     Uint byte_lit_size = sizeof(Eterm)*lit_size;
     Uint old_heap_size;
@@ -607,6 +609,7 @@ erts_garbage_collect_literals(Process* p, Eterm* literals, Uint lit_size)
     Uint area_size;
     Eterm* old_htop;
     Uint n;
+    struct erl_off_heap_header** prev;
 
     /*
      * Set GC state.
@@ -640,6 +643,9 @@ erts_garbage_collect_literals(Process* p, Eterm* literals, Uint lit_size)
     offset_heap(temp_lit, lit_size, offs, (char *) literals, byte_lit_size);
     offset_heap(p->heap, p->htop - p->heap, offs, (char *) literals, byte_lit_size);
     offset_rootset(p, offs, (char *) literals, byte_lit_size, p->arg_reg, p->arity);
+    if (oh) {
+	oh = (struct erl_off_heap_header *) ((Eterm *)(void *) oh + offs);
+    }
 
     /*
      * Now the literals are placed in memory that is safe to write into,
@@ -707,6 +713,45 @@ erts_garbage_collect_literals(Process* p, Eterm* literals, Uint lit_size)
     p->old_htop = old_htop;
 
     /*
+     * Prepare to sweep binaries. Since all MSOs on the new heap
+     * must be come before MSOs on the old heap, find the end of
+     * current MSO list and use that as a starting point.
+     */
+
+    if (oh) {
+	prev = &MSO(p).first;
+	while (*prev) {
+	    prev = &(*prev)->next;
+	}
+    }
+
+    /*
+     * Sweep through all binaries in the temporary literal area.
+     */
+
+    while (oh) {
+	if (IS_MOVED_BOXED(oh->thing_word)) {
+	    Binary* bptr;
+	    struct erl_off_heap_header* ptr;
+
+	    ptr = (struct erl_off_heap_header*) boxed_val(oh->thing_word);
+	    ASSERT(thing_subtag(ptr->thing_word) == REFC_BINARY_SUBTAG);
+	    bptr = ((ProcBin*)ptr)->val;
+
+	    /*
+	     * This binary has been copied to the heap.
+	     * We must increment its reference count and
+	     * link it into the MSO list for the process.
+	     */
+
+	    erts_refc_inc(&bptr->refc, 1);
+	    *prev = ptr;
+	    prev = &ptr->next;
+	}
+	oh = oh->next;
+    }
+
+    /*
      * We no longer need this temporary area.
      */
     erts_free(ERTS_ALC_T_TMP, (void *) temp_lit);