Add a way to force the use of the old block allocator

* Test that arrow can be exported when the block allocator is forced.

Tests/test_arrow.py

@@ -170,8 +170,7 @@ def test_multiblock_l_image():
     with pytest.raises(ValueError):
         (schema, arr) = img.__arrow_c_array__()
 
-
-def test_multiblock__rgba_image():
+def test_multiblock_rgba_image():
     block_size = Image.core.get_block_size()
 
     # check a 2 block image in 4 channel mode
@@ -192,8 +191,7 @@ def test_multiblock_l_schema():
     with pytest.raises(ValueError):
         schema = img.__arrow_c_schema__()
 
-
-def test_multiblock__rgba_schema():
+def test_multiblock_rgba_schema():
     block_size = Image.core.get_block_size()
 
     # check a 2 block image in 4 channel mode
@@ -201,4 +199,62 @@ def test_multiblock__rgba_schema():
     img = Image.new("RGBA", size, (128, 127, 126, 125))
 
     with pytest.raises(ValueError):
-        schema = img.__arrow_c_schema__()
+        schema= img.__arrow_c_schema__()
+
+
+def test_singleblock_l_image():
+    Image.core.set_use_block_allocator(1)
+
+    block_size = Image.core.get_block_size()
+
+    # check a 2 block image in 4 channel mode
+    size = (4096, 2* (block_size//4096))
+    img = Image.new('L', size, 128)
+    assert img.im.isblock()
+
+    (schema, arr) = img.__arrow_c_array__()
+    assert schema
+    assert arr
+
+    Image.core.set_use_block_allocator(0)
+
+def test_singleblock_rgba_image():
+    Image.core.set_use_block_allocator(1)
+    block_size = Image.core.get_block_size()
+
+    # check a 2 block image in 4 channel mode
+    size = (4096, (block_size//4096) //2)
+    img = Image.new('RGBA', size, (128,127,126,125))
+    assert img.im.isblock()
+
+    (schema, arr) = img.__arrow_c_array__()
+    assert schema
+    assert arr
+    Image.core.set_use_block_allocator(0)
+
+
+def test_singleblock_l_schema():
+    Image.core.set_use_block_allocator(1)
+    block_size = Image.core.get_block_size()
+
+    # check a 2 block image in single channel mode
+    size = (4096, 2*block_size//4096)
+    img = Image.new('L', size, 128)
+    assert img.im.isblock()
+
+    schema = img.__arrow_c_schema__()
+    assert schema
+    Image.core.set_use_block_allocator(0)
+
+def test_singleblock_rgba_schema():
+    Image.core.set_use_block_allocator(1)
+    block_size = Image.core.get_block_size()
+
+    # check a 2 block image in 4 channel mode
+    size = (4096, (block_size//4096) //2)
+    img = Image.new('RGBA', size, (128,127,126,125))
+    assert img.im.isblock()
+
+    schema= img.__arrow_c_schema__()
+    assert schema
+    Image.core.set_use_block_allocator(0)

src/_imaging.c

@@ -4192,6 +4192,22 @@ _set_blocks_max(PyObject *self, PyObject *args) {
     return Py_None;
 }
 
+static PyObject *
+_set_use_block_allocator(PyObject *self, PyObject *args) {
+    int use_block_allocator;
+    if (!PyArg_ParseTuple(args, "i:set_use_block_allocator", &use_block_allocator)) {
+        return NULL;
+    }
+    ImagingMemorySetBlockAllocator(&ImagingDefaultArena, use_block_allocator);
+    Py_RETURN_NONE;
+}
+
+
+static PyObject *
+_get_use_block_allocator(PyObject *self, PyObject *args) {
+    return PyLong_FromLong(ImagingDefaultArena.use_block_allocator);
+}
+
 static PyObject *
 _clear_cache(PyObject *self, PyObject *args) {
     int i = 0;
@@ -4399,9 +4415,11 @@ static PyMethodDef functions[] = {
     {"get_alignment", (PyCFunction)_get_alignment, METH_VARARGS},
     {"get_block_size", (PyCFunction)_get_block_size, METH_VARARGS},
     {"get_blocks_max", (PyCFunction)_get_blocks_max, METH_VARARGS},
+    {"get_use_block_allocator", (PyCFunction)_get_use_block_allocator, METH_VARARGS},
     {"set_alignment", (PyCFunction)_set_alignment, METH_VARARGS},
     {"set_block_size", (PyCFunction)_set_block_size, METH_VARARGS},
     {"set_blocks_max", (PyCFunction)_set_blocks_max, METH_VARARGS},
+    {"set_use_block_allocator", (PyCFunction)_set_use_block_allocator, METH_VARARGS},
     {"clear_cache", (PyCFunction)_clear_cache, METH_VARARGS},
 
     {NULL, NULL} /* sentinel */

src/libImaging/Imaging.h

@@ -178,6 +178,7 @@ typedef struct ImagingMemoryArena {
     int stats_reallocated_blocks; /* Number of blocks which were actually reallocated
                                      after retrieving */
     int stats_freed_blocks;       /* Number of freed blocks */
+    int use_block_allocator;      /* don't use arena, use block allocator */
 #ifdef Py_GIL_DISABLED
     PyMutex mutex;
 #endif
@@ -191,6 +192,8 @@ extern int
 ImagingMemorySetBlocksMax(ImagingMemoryArena arena, int blocks_max);
 extern void
 ImagingMemoryClearCache(ImagingMemoryArena arena, int new_size);
+extern void
+ImagingMemorySetBlockAllocator(ImagingMemoryArena arena, int use_block_allocator);
 
 extern Imaging
 ImagingNew(const char *mode, int xsize, int ysize);

src/libImaging/Storage.c

@@ -341,6 +341,7 @@ struct ImagingMemoryArena ImagingDefaultArena = {
     0,
     0,
     0,  // Stats
+    0,  // use_block_allocator
 #ifdef Py_GIL_DISABLED
     {0},
 #endif
@@ -373,6 +374,12 @@ ImagingMemorySetBlocksMax(ImagingMemoryArena arena, int blocks_max) {
     return 1;
 }
 
+void
+ImagingMemorySetBlockAllocator(ImagingMemoryArena arena, int use_block_allocator) {
+    arena->use_block_allocator = use_block_allocator;
+}
+
+
 void
 ImagingMemoryClearCache(ImagingMemoryArena arena, int new_size) {
     while (arena->blocks_cached > new_size) {
@@ -649,11 +656,17 @@ ImagingNewInternal(const char *mode, int xsize, int ysize, int dirty) {
 
 Imaging
 ImagingNew(const char *mode, int xsize, int ysize) {
+    if (ImagingDefaultArena.use_block_allocator) {
+        return ImagingNewBlock(mode, xsize, ysize);
+    }
     return ImagingNewInternal(mode, xsize, ysize, 0);
 }
 
 Imaging
 ImagingNewDirty(const char *mode, int xsize, int ysize) {
+    if (ImagingDefaultArena.use_block_allocator) {
+        return ImagingNewBlock(mode, xsize, ysize);
+    }
     return ImagingNewInternal(mode, xsize, ysize, 1);
 }