程序也有死鎖與遞迴鎖，在程序那裡忘記說了，放到這裡一切說了額

所謂死鎖： 是指兩個或兩個以上的程序或執行緒在執行過程中，因爭奪資源而造成的一種互相等待的現象，若無外力作用，它們都將無法推進下去。此時稱系統處於死鎖狀態或系統產生了死鎖，這些永遠在互相等待的程序稱為死鎖程序，如下就是死鎖

 1 from threading import Lock as Lock
 2 import time
 3 mutexA=Lock()
 4 mutexA.acquire()
 5 mutexA.acquire()
 6 print(123)
 7 mutexA.release()
 8 mutexA.release()
 
 9 
10 死鎖

解決方法，遞迴鎖，在Python中為了支援在同一執行緒中多次請求同一資源，python提供了可重入鎖RLock。

這個RLock內部維護著一個Lock和一個counter變數，counter記錄了acquire的次數，從而使得資源可以被多次require。直到一個執行緒所有的acquire都被release，其他的執行緒才能獲得資源。上面的例子如果使用RLock代替Lock，則不會發生死鎖：

from threading import RLock as Lock
import time
mutexA=Lock()
mutexA.acquire()
mutexA.acquire()
 
print(123)
mutexA.release()
mutexA.release()

遞迴鎖RLock

典型問題: 科學家吃麵

 1 import time
 2 from threading import Thread,Lock
 3 noodle_lock = Lock()
 4 fork_lock = Lock()
 5 def eat1(name):
 6     noodle_lock.acquire()
 7     print('%s 搶到了麵條'%name)
 8     fork_lock.acquire()
 9     print('%s 搶到了叉子
 
'%name)
10     print('%s 吃麵'%name)
11     fork_lock.release()
12     noodle_lock.release()
13 
14 def eat2(name):
15     fork_lock.acquire()
16     print('%s 搶到了叉子' % name)
17     time.sleep(1)
18     noodle_lock.acquire()
19     print('%s 搶到了麵條' % name)
20     print('%s 吃麵' % name)
21     noodle_lock.release()
22     fork_lock.release()
23 
24 for name in ['哪吒','egon','yuan']:
25     t1 = Thread(target=eat1,args=(name,))
26     t2 = Thread(target=eat2,args=(name,))
27     t1.start()
28     t2.start()
29 
30 死鎖問題

 1 import time
 2 from threading import Thread,RLock
 3 fork_lock = noodle_lock = RLock()
 4 def eat1(name):
 5     noodle_lock.acquire()
 6     print('%s 搶到了麵條'%name)
 7     fork_lock.acquire()
 8     print('%s 搶到了叉子'%name)
 9     print('%s 吃麵'%name)
10     fork_lock.release()
11     noodle_lock.release()
12 
13 def eat2(name):
14     fork_lock.acquire()
15     print('%s 搶到了叉子' % name)
16     time.sleep(1)
17     noodle_lock.acquire()
18     print('%s 搶到了麵條' % name)
19     print('%s 吃麵' % name)
20     noodle_lock.release()
21     fork_lock.release()
22 
23 for name in ['哪吒','egon','yuan']:
24     t1 = Thread(target=eat1,args=(name,))
25     t2 = Thread(target=eat2,args=(name,))
26     t1.start()
27     t2.start()
28 
29 遞迴鎖解決死鎖問題