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];