Block allocator scratch

src/basic_alloc.cpp

@@ -331,7 +331,34 @@ API void *BlockArenaAllocatorProc(void *object, int kind, void *p, size_t size)
 }
 
 #if OS_WASM
+BlockArena ScratchArenas[4];
 API void InitScratch() {
+    for (int i = 0; i < 4; i += 1) {
+        if (!ScratchArenas[i].blocks) Init(&ScratchArenas[i]);
+    }
+}
+
+API BlockArena *GetScratchEx(BlockArena **conflicts, int conflict_count) {
+    BlockArena *unoccupied = 0;
+    for (int i = 0; i < Lengthof(ScratchArenas); i += 1) {
+        BlockArena *from_pool = &ScratchArenas[i];
+        unoccupied = from_pool;
+        for (int conflict_i = 0; conflict_i < conflict_count; conflict_i += 1) {
+            BlockArena *from_conflict = conflicts[conflict_i];
+            if (from_pool == from_conflict) {
+                unoccupied = 0;
+                break;
+            }
+        }
+
+        if (unoccupied) {
+            break;
+        }
+    }
+
+    // Failed to get free scratch memory, this is a fatal error, this shouldnt happen
+    Assert(unoccupied);
+    return unoccupied;
 }
 #else
 thread_local VirtualArena ScratchArenas[4];

src/basic_alloc.h

@@ -98,16 +98,43 @@ API void          Release(VirtualArena *arena);
 ///////////////////////////////
 // Scratch
 #if OS_WASM
+extern BlockArena ScratchArenas[4];
+API BlockArena *GetScratchEx(BlockArena **conflicts, int conflict_count);
 struct Scratch {
-    BlockArena arena = {};
-    Scratch() {}
-    Scratch(BlockArena *conflict) {}
-    Scratch(BlockArena *c1, BlockArena *c2) {}
-    Scratch(Allocator conflict) {}
-    Scratch(Allocator c1, Allocator c2) {}
-    ~Scratch() { Release(&arena); }
-    operator BlockArena *() { return &arena; }
-    operator Allocator() { return arena; }
+    BlockArena *arena;
+    U8 *p;
+    Scratch() {arena = &ScratchArenas[0]; if (!arena->blocks) Init(arena); p = arena->start; arena->refs += 1;}
+    Scratch(BlockArena *conflict) {
+        BlockArena *conf[] = {conflict};
+        arena = GetScratchEx(conf, Lengthof(conf));
+        if (!arena->blocks) Init(arena);
+        p = arena->start;
+        arena->refs += 1;
+    }
+    Scratch(BlockArena *c1, BlockArena *c2) {
+        BlockArena *conf[] = {c1, c2};
+        arena = GetScratchEx(conf, Lengthof(conf));
+        if (!arena->blocks) Init(arena);
+        p = arena->start;
+        arena->refs += 1;
+    }
+    Scratch(Allocator conflict) {
+        BlockArena *conf[] = {(BlockArena *)conflict.object};
+        arena = GetScratchEx(conf, Lengthof(conf));
+        if (!arena->blocks) Init(arena);
+        p = arena->start;
+        arena->refs += 1;
+    }
+    Scratch(Allocator c1, Allocator c2) {
+        BlockArena *conf[] = {(BlockArena *)c1.object, (BlockArena *)c2.object};
+        arena = GetScratchEx(conf, Lengthof(conf));
+        if (!arena->blocks) Init(arena);
+        p = arena->start;
+        arena->refs += 1;
+    }
+    ~Scratch() { Unwind(arena, p); arena->refs -= 1; }
+    operator BlockArena *() { return arena; }
+    operator Allocator() { return *arena; }
   private: // @Note: Disable copy constructors, cause its error prone
     Scratch(Scratch &arena);
     Scratch(Scratch &arena, Scratch &a2);