mmap: add a size argument to mmapread
With this argument, we can control the size of the mmap created. (previously it
was always the whole file.
Differential Revision: https://phab.mercurial-scm.org/D7808
--- a/mercurial/util.py Tue Jan 07 12:26:37 2020 +0100
+++ b/mercurial/util.py Tue Jan 07 12:09:36 2020 +0100
@@ -415,10 +415,16 @@
return data
-def mmapread(fp):
+def mmapread(fp, size=None):
+ if size == 0:
+ # size of 0 to mmap.mmap() means "all data"
+ # rather than "zero bytes", so special case that.
+ return b''
+ elif size is None:
+ size = 0
try:
fd = getattr(fp, 'fileno', lambda: fp)()
- return mmap.mmap(fd, 0, access=mmap.ACCESS_READ)
+ return mmap.mmap(fd, size, access=mmap.ACCESS_READ)
except ValueError:
# Empty files cannot be mmapped, but mmapread should still work. Check
# if the file is empty, and if so, return an empty buffer.