numpy.memmap 到 Image.frombuffer - 无需复制

Question

我正在尝试对在另一个进程中创建的文件进行内存映射，以用作共享帧缓冲区。我不想复制数据，因为我想使用 PIL ImageDraw 函数来操作映射的缓冲区，然后刷新更改。我对 python 和内存映射文件相当陌生。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 的frombuffer。原来它将readonly 标志设置为1。我不确定副作用，但如果你将标志设置为零，你的代码就可以工作：

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