Pass continuations for success and failure cases (#788)

This PR provides a templated parameter to the allocation routines. This can be used to add special behaviour in
both the successful allocation behaviour, and in the failing
to allocate cases.

The intent of this is two enable two future features
* set_new_handler - so that the failure case doesn't just set ENOMEM, and return nullptr.  But can handle both the Windows and C++ versions of (_)set_new_handler.
* The success handler can be used to add checking, zeroing and in the future storing precise size information in metadata for each allocation.

Author: mjp41

fuzzing/snmalloc-fuzzer.cpp

@@ -166,15 +166,15 @@ void snmalloc_random_walk(
       case EventKind::AllocZero:
       {
         auto ptr =
-          static_cast<char*>(scoped->alloc<snmalloc::YesZero>(e.size_or_index));
+          static_cast<char*>(scoped->alloc<snmalloc::Zero>(e.size_or_index));
         results.emplace_back(0, ptr, e.size_or_index);
         break;
       }
 
       case EventKind::AllocNoZero:
       {
         auto ptr =
-          static_cast<char*>(scoped->alloc<snmalloc::NoZero>(e.size_or_index));
+          static_cast<char*>(scoped->alloc<snmalloc::Uninit>(e.size_or_index));
         std::fill(ptr, ptr + e.size_or_index, e.filler);
         results.emplace_back(e.filler, ptr, e.size_or_index);
         break;

src/snmalloc/backend/backend.h

@@ -59,7 +59,6 @@ namespace snmalloc
 
       if (p == nullptr)
       {
-        errno = ENOMEM;
         return nullptr;
       }
 
@@ -112,7 +111,6 @@ namespace snmalloc
 
       if (meta == nullptr)
       {
-        errno = ENOMEM;
         return {nullptr, nullptr};
       }
 
@@ -124,7 +122,6 @@ namespace snmalloc
       if (p == nullptr)
       {
         local_state.get_meta_range().dealloc_range(meta_cap, meta_size);
-        errno = ENOMEM;
 #ifdef SNMALLOC_TRACING
         message<1024>("Out of memory");
 #endif

src/snmalloc/global/globalalloc.h

@@ -321,24 +321,24 @@ namespace snmalloc
     return sizeclass_full_to_size(entry.get_sizeclass());
   }
 
-  template<size_t size, ZeroMem zero_mem = NoZero, size_t align = 1>
+  template<size_t size, typename Conts = Uninit, size_t align = 1>
   SNMALLOC_FAST_PATH_INLINE void* alloc()
   {
-    return ThreadAlloc::get().alloc<zero_mem, ThreadAlloc::CheckInit>(
+    return ThreadAlloc::get().alloc<Conts, ThreadAlloc::CheckInit>(
       aligned_size(align, size));
   }
 
-  template<ZeroMem zero_mem = NoZero, size_t align = 1>
+  template<typename Conts = Uninit, size_t align = 1>
   SNMALLOC_FAST_PATH_INLINE void* alloc(size_t size)
   {
-    return ThreadAlloc::get().alloc<zero_mem, ThreadAlloc::CheckInit>(
+    return ThreadAlloc::get().alloc<Conts, ThreadAlloc::CheckInit>(
       aligned_size(align, size));
   }
 
-  template<ZeroMem zero_mem = NoZero>
+  template<typename Conts = Uninit>
   SNMALLOC_FAST_PATH_INLINE void* alloc_aligned(size_t align, size_t size)
   {
-    return ThreadAlloc::get().alloc<zero_mem, ThreadAlloc::CheckInit>(
+    return ThreadAlloc::get().alloc<Conts, ThreadAlloc::CheckInit>(
       aligned_size(align, size));
   }
 

src/snmalloc/global/libc.h

@@ -47,7 +47,7 @@ namespace snmalloc::libc
     {
       return set_error();
     }
-    return alloc<ZeroMem::YesZero>(sz);
+    return alloc<Zero>(sz);
   }
 
   SNMALLOC_FAST_PATH_INLINE void* realloc(void* ptr, size_t size)