python - numpy.memmap 到 Image.frombuffer - 不复制

Question

我正在尝试内存映射在另一个进程中创建的文件以用作共享帧缓冲区。我不想复制数据，因为我想使用 PIL ImageDraw 函数来操作映射缓冲区，然后刷新更改。我对 python 和内存映射文件还很陌生。我错过了什么？

# This is my setup code that creates a memory mapped array - seems to work
buf = np.memmap('/tmp/shared_mem', mode="readwrite", dtype="uint32", shape=(60,60))

# Here I build a PIL Image from the memory mapped data and correct layout, etc...
img = Image.frombuffer('RGBA', (60, 60), buf)
dr = ImageDraw.Draw(img)

# Changes using ImageDraw or putpixel do not show in the mapped file.
dr.rectangle(((0,0), (60,60)), fill="red")
buf.flush()

# Changes using numpy methods work just fine.
buf.fill(0)
buf.flush()

Answer 1

我查看了 source code对于 frombuffer。原来它将 readonly 标志设置为 1。我不确定副作用，但如果您将标志设置为零，您的代码就可以工作:

buf = np.memmap(fname, mode="readwrite", dtype="uint32", shape=(n,n))
buf[:] = 0
img = Image.frombuffer('RGBA', (n, n), buf)
img.readonly = 0
dr = ImageDraw.Draw(img)
dr.rectangle(((0,0), (n,n)), fill="red")
print buf[0,0]
# 4278190335