New submission from STINNER Victor:
Example:
with open("x", "w", encoding="utf-8") as fp:
fp.write("HERE")
fp.close()
syscalls:
14249 open("x", O_WRONLY|O_CREAT|O_TRUNC|O_CLOEXEC, 0666) = 3
14249 fstat(3, {st_mode=S_IFREG|0664, st_size=0, ...}) = 0
14249 ioctl(3, TCGETS, 0x7fff07d43330) = -1 ENOTTY (Inappropriate ioctl for
device)
14249 lseek(3, 0, SEEK_CUR) = 0
14249 lseek(3, 0, SEEK_CUR) = 0
14249 lseek(3, 0, SEEK_CUR) = 0
14249 write(3, "HERE", 4) = 4
14249 close(3) = 0
I only expected 3 syscalls: open, write, close.
* fstat() is used by the FileIO constructor to check if the file is a directory
or not, and to get the block size
* ioctl() comes from open() which checks if the file is a TTY or not, to decide
how to configure buffering
* the first lseek() is used by the BuffererWriter constructor to initialize the
private abs_pos attribute
* the second lseek() is used by the TextIOWrapper constructor to check if the
underlying file object (buffered writer) is seekable or not
* the last lseek() is used to create the cookie object in TextIOWrapper
constructor
Can we maybe reduce the number of lseek() to a single syscall?
For example, BuffererWriter constructor calls FileIO.tell(): can't this method
set the seekable attribute depending on lseek() success, as the FileIO.seekable
property?
----------
messages: 292744
nosy: haypo, pitrou, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Open a file in text mode requires too many syscalls
type: performance
versions: Python 3.7
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue30228>
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