bisect: avoid copying ancestor list for non-merge commits
During a bisection, hg needs to compute a list of all ancestors for every
candidate commit. This is accomplished via a bottom-up traversal of the set of
candidates, during which each revision's ancestor list is populated using the
ancestor list of its parent(s). Previously, this involved copying the entire
list, which could be very long in if the bisection range was large.
To help improve this, we can observe that each candidate commit is visited
exactly once, at which point its ancestor list is copied into its children's
lists and then dropped. In the case of non-merge commits, a commit's ancestor
list consists exactly of its parent's list plus itself. This means that we can
trivially reuse the parent's existing list for one of its non-merge children,
which avoids copying entirely if that commit is the parent's only child. This
makes bisections over linear ranges of commits much faster.
During some informal testing in the large publicly-available `mozilla-central`
repository, this noticeably sped up bisections over large ranges of history:
Setup:
$ cd mozilla-central
$ hg bisect --reset
$ hg bisect --good 0
$ hg log -r tip -T '{rev}\n'
628417
Test:
$ time hg bisect --bad tip --noupdate
Before:
real 3m35.927s
user 3m35.553s
sys 0m0.319s
After:
real 1m41.142s
user 1m40.810s
sys 0m0.285s
#!/usr/bin/env python3
import os
import signal
import sys
import time
if os.name == 'nt':
import ctypes
_BOOL = ctypes.c_long
_DWORD = ctypes.c_ulong
_UINT = ctypes.c_uint
_HANDLE = ctypes.c_void_p
ctypes.windll.kernel32.CloseHandle.argtypes = [_HANDLE]
ctypes.windll.kernel32.CloseHandle.restype = _BOOL
ctypes.windll.kernel32.GetLastError.argtypes = []
ctypes.windll.kernel32.GetLastError.restype = _DWORD
ctypes.windll.kernel32.OpenProcess.argtypes = [_DWORD, _BOOL, _DWORD]
ctypes.windll.kernel32.OpenProcess.restype = _HANDLE
ctypes.windll.kernel32.TerminateProcess.argtypes = [_HANDLE, _UINT]
ctypes.windll.kernel32.TerminateProcess.restype = _BOOL
ctypes.windll.kernel32.WaitForSingleObject.argtypes = [_HANDLE, _DWORD]
ctypes.windll.kernel32.WaitForSingleObject.restype = _DWORD
def _check(ret, expectederr=None):
if ret == 0:
winerrno = ctypes.GetLastError()
if winerrno == expectederr:
return True
raise ctypes.WinError(winerrno)
def kill(pid, logfn, tryhard=True):
logfn('# Killing daemon process %d' % pid)
PROCESS_TERMINATE = 1
PROCESS_QUERY_INFORMATION = 0x400
SYNCHRONIZE = 0x00100000
WAIT_OBJECT_0 = 0
WAIT_TIMEOUT = 258
WAIT_FAILED = _DWORD(0xFFFFFFFF).value
handle = ctypes.windll.kernel32.OpenProcess(
PROCESS_TERMINATE | SYNCHRONIZE | PROCESS_QUERY_INFORMATION,
False,
pid,
)
if handle is None:
_check(0, 87) # err 87 when process not found
return # process not found, already finished
try:
r = ctypes.windll.kernel32.WaitForSingleObject(handle, 100)
if r == WAIT_OBJECT_0:
pass # terminated, but process handle still available
elif r == WAIT_TIMEOUT:
_check(ctypes.windll.kernel32.TerminateProcess(handle, -1))
elif r == WAIT_FAILED:
_check(0) # err stored in GetLastError()
# TODO?: forcefully kill when timeout
# and ?shorter waiting time? when tryhard==True
r = ctypes.windll.kernel32.WaitForSingleObject(handle, 100)
# timeout = 100 ms
if r == WAIT_OBJECT_0:
pass # process is terminated
elif r == WAIT_TIMEOUT:
logfn('# Daemon process %d is stuck')
elif r == WAIT_FAILED:
_check(0) # err stored in GetLastError()
except: # re-raises
ctypes.windll.kernel32.CloseHandle(handle) # no _check, keep error
raise
_check(ctypes.windll.kernel32.CloseHandle(handle))
else:
def kill(pid, logfn, tryhard=True):
try:
os.kill(pid, 0)
logfn('# Killing daemon process %d' % pid)
os.kill(pid, signal.SIGTERM)
if tryhard:
for i in range(10):
time.sleep(0.05)
os.kill(pid, 0)
else:
time.sleep(0.1)
os.kill(pid, 0)
logfn('# Daemon process %d is stuck - really killing it' % pid)
os.kill(pid, signal.SIGKILL)
except ProcessLookupError:
pass
def killdaemons(pidfile, tryhard=True, remove=False, logfn=None):
if not logfn:
logfn = lambda s: s
# Kill off any leftover daemon processes
try:
pids = []
with open(pidfile) as fp:
for line in fp:
try:
pid = int(line)
if pid <= 0:
raise ValueError
except ValueError:
logfn(
'# Not killing daemon process %s - invalid pid'
% line.rstrip()
)
continue
pids.append(pid)
for pid in pids:
kill(pid, logfn, tryhard)
if remove:
os.unlink(pidfile)
except IOError:
pass
if __name__ == '__main__':
if len(sys.argv) > 1:
(path,) = sys.argv[1:]
else:
path = os.environ["DAEMON_PIDS"]
killdaemons(path, remove=True)