Revert "internal/atlas: reintroduce a byte pool"

This reverts commit 7e17b25c56.

Reason: the current byte pool suppresses allocations to some extent, but doesn't suppress GCs.

Updates #1681

internal/atlas/bytes.go

@@ -1,93 +0,0 @@
-// Copyright 2023 The Ebitengine Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-package atlas
-
-import (
-	"runtime"
-	"sync"
-	"unsafe"
-)
-
-// allocBytesFromPool returns a byte slice with the given size.
-// The slice might be obtained from a cache, and might not be zero-cleared.
-func allocBytesFromPool(size int) []byte {
-	return theBytesPool.get(size)
-}
-
-type bytesPool struct {
-	pool [][]byte
-
-	m sync.Mutex
-}
-
-var theBytesPool bytesPool
-
-func (b *bytesPool) get(size int) []byte {
-	if size == 0 {
-		return nil
-	}
-
-	if bs := b.getFromCache(size); bs != nil {
-		return bs
-	}
-
-	bs := make([]byte, size)
-	b.setFinalizer(bs)
-	return bs
-}
-
-func (b *bytesPool) getFromCache(size int) []byte {
-	b.m.Lock()
-	defer b.m.Unlock()
-
-	for i, bs := range b.pool {
-		if cap(bs) < size {
-			continue
-		}
-
-		copy(b.pool[i:], b.pool[i+1:])
-		b.pool[len(b.pool)-1] = nil
-		b.pool = b.pool[:len(b.pool)-1]
-
-		bs = bs[:size]
-		b.setFinalizer(bs)
-		return bs
-	}
-
-	return nil
-}
-
-func (b *bytesPool) setFinalizer(bs []byte) {
-	c := cap(bs)
-	runtime.SetFinalizer(&bs[0], func(ptr *byte) {
-		b.m.Lock()
-		defer b.m.Unlock()
-
-		b.pool = append(b.pool, unsafe.Slice(ptr, c))
-
-		// GC the pool. The size limitation is arbitrary.
-		for len(b.pool) >= 32 || b.totalSize() >= 1024*1024*1024 {
-			b.pool = b.pool[1:]
-		}
-	})
-}
-
-func (b *bytesPool) totalSize() int {
-	var s int
-	for _, bs := range b.pool {
-		s += len(bs)
-	}
-	return s
-}

internal/atlas/image.go

@@ -482,13 +482,15 @@ func (i *Image) writePixels(pix []byte, region image.Rectangle) {
 		}
 
 		// Copy pixels in the case when pix is modified before the graphics command is executed.
-		pix2 := allocBytesFromPool(len(pix))
+		// TODO: Create byte slices from a pool.
+		pix2 := make([]byte, len(pix))
 		copy(pix2, pix)
 		i.backend.restorable.WritePixels(pix2, region)
 		return
 	}
 
-	pixb := allocBytesFromPool(4 * r.Dx() * r.Dy())
+	// TODO: Create byte slices from a pool.
+	pixb := make([]byte, 4*r.Dx()*r.Dy())
 
 	// Clear the edges. pixb might not be zero-cleared.
 	// TODO: These loops assume that paddingSize is 1.