OE fixes (#157)

* Only compile OE PAL if required.

* OE:reserve: Fix bug in loop.

* Handle out of memory by returning nullptr.

src/mem/alloc.h

@@ -877,7 +877,7 @@ namespace snmalloc
         large_allocator.template alloc<NoZero, allow_reserve>(
           0, SUPERSLAB_SIZE));
 
-      if ((allow_reserve == NoReserve) && (super == nullptr))
+      if (super == nullptr)
         return super;
 
       super->init(public_state());
@@ -939,7 +939,7 @@ namespace snmalloc
 
         super = get_superslab<allow_reserve>();
 
-        if ((allow_reserve == NoReserve) && (super == nullptr))
+        if (super == nullptr)
           return nullptr;
 
         Slab* slab = super->alloc_short_slab(sizeclass);
@@ -949,7 +949,7 @@ namespace snmalloc
 
       Superslab* super = get_superslab<allow_reserve>();
 
-      if ((allow_reserve == NoReserve) && (super == nullptr))
+      if (super == nullptr)
         return nullptr;
 
       Slab* slab = super->alloc_slab(sizeclass);
@@ -1025,6 +1025,9 @@ namespace snmalloc
         if ((allow_reserve == NoReserve) && (slab == nullptr))
           return nullptr;
 
+        if (slab == nullptr)
+          return nullptr;
+
         sl.insert_back(slab->get_link());
       }
       auto& ffl = small_fast_free_lists[sizeclass];
@@ -1156,7 +1159,7 @@ namespace snmalloc
           large_allocator.template alloc<NoZero, allow_reserve>(
             0, SUPERSLAB_SIZE));
 
-        if ((allow_reserve == NoReserve) && (slab == nullptr))
+        if (slab == nullptr)
           return nullptr;
 
         slab->init(public_state(), sizeclass, rsize);
@@ -1230,10 +1233,12 @@ namespace snmalloc
 
       void* p = large_allocator.template alloc<zero_mem, allow_reserve>(
         large_class, size);
+      if (likely(p != nullptr))
+      {
+        chunkmap().set_large_size(p, size);
 
-      chunkmap().set_large_size(p, size);
-
-      stats().large_alloc(large_class);
+        stats().large_alloc(large_class);
+      }
       return p;
     }
 

src/mem/largealloc.h

@@ -125,6 +125,12 @@ namespace snmalloc
     {
       // Reserve the smallest large_class which is SUPERSLAB_SIZE
       void* r = reserve<false>(0);
+
+      if (r == nullptr)
+        Pal::error(
+          "Unrecoverable internal error: \
+          failed to allocator internal data structure.");
+
       PAL::template notify_using<NoZero>(r, OS_PAGE_SIZE);
 
       bump = r;
@@ -274,6 +280,9 @@ namespace snmalloc
         size_t request = bits::max(size * 4, SUPERSLAB_SIZE * 8);
         void* p = PAL::template reserve<false>(request);
 
+        if (p == nullptr)
+          return nullptr;
+
         address_t p0 = address_cast(p);
         address_t start = bits::align_up(p0, align);
         address_t p1 = p0 + request;
@@ -354,6 +363,8 @@ namespace snmalloc
       if (p == nullptr)
       {
         p = memory_provider.template reserve<false>(large_class);
+        if (p == nullptr)
+          return nullptr;
         memory_provider.template notify_using<zero_mem>(p, size);
       }
       else