GH-130328: pasting in new REPL is slow on Windows

[chris-eibl]

The reason why pasting is so slow on Windows (especially in the legacy console case where virtual terminal mode - and thus bracketed paste - is disabled):

cpython/Lib/_pyrepl/reader.py

Lines 702 to 706 in 9f5994b

	whileTrue:
	# We use the same timeout as in readline.c: 100ms
	self.run_hooks()
	self.console.wait(100)
	event=self.console.get_event(block=False)

and

cpython/Lib/_pyrepl/windows_console.py

Lines 523 to 532 in 9f5994b

	defwait(self, timeout: float|None) ->bool:
	"""Wait for an event."""
	# Poor man's Windows select loop
	start_time=time.time()
	whileTrue:
	ifmsvcrt.kbhit(): # type: ignore[attr-defined]
	returnTrue
	iftimeoutandtime.time() -start_time>timeout/1000:
	returnFalse
	time.sleep(0.01)

It is interesting, that msvcrt.kbhit() returns True in case of pasting, but if that weren't the case, we'd hit the 100ms timeout and would be even way slower. However, msvcrt.kbhit() is very slow in case of the legacy console, and it is called at least twice as often, because we get a key up and a key down event - but only a key down event in the virtual terminal case. If the pasted input contains upper case letters, we additionally get a "shift key pressed" event - so in the worst case, msvcrt.kbhit() gets called 3 times more often (and each call is slower).

Output of python.bat -m cProfile -m _pyrepl when pasting the "test value" given in the OP for a legacy console:

 ncalls tottime percall cumtime percall filename:lineno(function) 50/1 0.010 0.000 17.202 17.202{built-in method builtins.exec} 1 0.000 0.000 17.202 17.202 <frozen runpy>:201(run_module) 1 0.000 0.000 17.199 17.199 <frozen runpy>:65(_run_code) 1 0.000 0.000 17.199 17.199 __main__.py:1(<module>) 1 0.000 0.000 17.112 17.112 main.py:24(interactive_console) 1 0.000 0.000 17.112 17.112 simple_interact.py:99(run_multiline_interactive_console) 5 0.000 0.000 17.111 3.422 readline.py:375(multiline_input) 5 0.004 0.001 17.111 3.422 reader.py:741(readline) 3090 0.036 0.000 17.103 0.006 reader.py:694(handle1) 6210 0.013 0.000 13.714 0.002 windows_console.py:523(wait) 6236 13.433 0.002 13.433 0.002{built-in method msvcrt.kbhit} 

Here the relevant line in case of virtual terminal:

 3270 0.554 0.000 0.554 0.000{built-in method msvcrt.kbhit} 

The fix is to use WaitForSingleObject

defwait(self, timeout: float|None) ->bool: """Wait for an event."""ret=WaitForSingleObject(InHandle, int(timeout)) ifret==WAIT_FAILED: raiseWinError(ctypes.get_last_error())

which speeds up especially the legacy console (times in seconds):

	legacy terminal	virtual terminal
before	15.6	0.89
after	1.8	0.26

Note, see also #132440 (comment):

• legacy terminal: manually start cmd.exe. Timings gotten by pasting

import time t1 = time.time() <"test value" given in the OP> print(time.time() - t1) 

• virtual terminal: power shell via Windows terminal. Timings gotton by temporarily patching commands.py:

importtimeclassenable_bracketed_paste(Command): defdo(self) ->None: self.reader.bp_begin=time.perf_counter() self.reader.paste_mode=Trueself.reader.in_bracketed_paste=Trueclassdisable_bracketed_paste(Command): defdo(self) ->None: print("bracketed_paste took %5.2f s"% (time.perf_counter() -self.reader.bp_begin, )) self.reader.paste_mode=Falseself.reader.in_bracketed_paste=Falseself.reader.dirty=True

• Issue: Pasting in new REPL is slow #130328

[sergey-miryanov]

Good analysis and speedup! 👍

[chris-eibl]

Now we are nicely in sync with unix_console.py

cpython/Lib/_pyrepl/unix_console.py

Lines 400 to 401 in e1c09ff

	ifnotblockandnotself.wait(timeout=0):
	returnNone

[Fidget-Spinner]

We generally don't backport perf fixes unless they lead to a denial-of-service problem (so usually like an exponential-time algorithm), or result in a serious bug. So I'm removing the backport label.

[Fidget-Spinner]

On second thought, "slow" is perhaps an understatement. So once this is merged, let's ping Thomas to ask for his permission to backport to 3.13

[chris-eibl]

Yeah, in case of the legacy console pasting of the 30 + 3 lines given by the OP takes 15 seconds, and this brings it down to 1.8. Most people will hopefully use a virtual terminal, where the situation is much less severe. After all, the new REPL can be disabled using https://docs.python.org/3/using/cmdline.html#envvar-PYTHON_BASIC_REPL.

3 more lines added by me for easier benchmarking #130328 (comment)

import time t1 = time.time() 

"test value" given in the OP

"""1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890
1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890"""

print(time.time() - t1) 

[pablogsal]

If @ambv has not checked this this in a couple of days ping me and I will do a pass and land it. Thanks a lot for looking into this @chris-eibl ❤️

[ambv]

Thanks for the fix, Chris!

[Fidget-Spinner]

@Yhg1s seeking permission to backport this to 3.13.

According to Chris, it takes 15 seconds to paste 58 lines in the new repl in 3.13. Do you think that's slow enough to be worth backporting?

[chris-eibl]

@Yhg1s friendly ping and also asking @ambv whether this is worth backporting to 3.13?