[英]Find threading.Lock's futex id
我想檢測一個大型Python項目,以便能夠調試如下所示的生產問題:
23321 07:49:57.925037 futex(0x23b2c20, FUTEX_WAIT_PRIVATE, 0, NULL <unfinished ...>
23321 07:50:12.435793 <... futex resumed> ) = 0
在這里,線程在某個鎖(或條件變量)上等待了14.4秒。
我不確定該鎖是在Python代碼中還是在第三方C擴展中創建的,但是從統計學上來說,Python是一個不錯的猜測。
在我附加strace
,這個futex已經創建了。 我懷疑它是在應用程序啟動期間創建的。
我想戳一下threading.Lock()
和threading.Condition()
對象,並找出它們的底層futex ID。
至少我要記錄這些ID,以便以后,如果我必須跟蹤一個正在運行的應用程序,則可以解析我看到的符合邏輯的futex調用。
您可以通過rr記錄程序的執行,然后可以設置條件斷點,如下所示:
b futex if $rdi==0x23b2c20
我設法為Python2破解了一些東西,這是一個演示:
$ strace -T -e signal=none -e futex python2 test.py
futex(0x7f6da47be0a8, FUTEX_WAKE_PRIVATE, 2147483647) = 0 <0.000006>
('futex address', '0x55de8d1105b0')
futex(0x55de8d123a30, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, ffffffff) = 0 <0.000038>
futex(0x55de8d074bf0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, ffffffff) = 0 <0.000032>
futex(0x55de8d074bf0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, ffffffff) = 0 <0.000036>
before
futex(0x55de8d1105b0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, ffffffff) = 0 <5.017658>
inside
+++ exited with 0 +++
請注意,Python和strace
報告相同的futex地址0x55de8d1105b0
碼:
import threading
import time
import sys
import ctypes
l = threading.Lock()
if sys.getsizeof(l) == 48:
OFFSET = 4 # debug build: next, prev, refcnt, type, payload(lock_lock, ...)
elif sys.getsizeof(l) == 32:
OFFSET = 2 # normal build: refcnt, type, payload(lock_lock, ...)
else:
assert 0, "Don't do this shit to me"
lp = ctypes.cast(id(l), ctypes.POINTER(ctypes.POINTER(ctypes.c_ubyte)))[OFFSET]
print("futex address", hex(ctypes.addressof(lp.contents)))
class holder(threading.Thread):
def run(self):
with l:
time.sleep(5)
holder().start()
print("before")
with l:
print("inside")
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