C 使用信号灯在睡眠理发师中打印
我正在尝试使用pthreads和信号量在C中实现一个睡眠理发师问题的解决方案,唯一的部分要求是每个动作发生时都必须打印出来,例如: 理发师睡着了 顾客把理发师叫醒了 顾客在等理发师 客户离开是因为没有座位,只能在一段随机时间后返回 顾客正在理发 顾客已经离开了商店 我研究这个问题已经有一段时间了,结果是出现了各种各样的死锁,或者语句打印出了问题 这个问题的解决方案在这里并不完全适用,因为它会导致每次报表打印,例如理发师睡着后,客户叫醒理发师,或者由于上下文切换而导致报表打印混乱,这可能是一个真正的问题,也可能不是一个真正的问题 我当前的解决方案是伪代码,如下所示:C 使用信号灯在睡眠理发师中打印,c,multithreading,concurrency,pthreads,semaphore,C,Multithreading,Concurrency,Pthreads,Semaphore,我正在尝试使用pthreads和信号量在C中实现一个睡眠理发师问题的解决方案,唯一的部分要求是每个动作发生时都必须打印出来,例如: 理发师睡着了 顾客把理发师叫醒了 顾客在等理发师 客户离开是因为没有座位,只能在一段随机时间后返回 顾客正在理发 顾客已经离开了商店 我研究这个问题已经有一段时间了,结果是出现了各种各样的死锁,或者语句打印出了问题 这个问题的解决方案在这里并不完全适用,因为它会导致每次报表打印,例如理发师睡着后,客户叫醒理发师,或者由于上下文切换而导致报表打印混乱,这可能是一个真正
int chairs = N # available chairs
bool is_sleeping = false
bool is_cutting = false
bool finished = false # All customers taken care of (Changed in main)
# Semaphores for read/write access
semaphore rw_chairs = 1
semaphore rw_sleeping = 1
semaphore rw_cutting = 1
semaphore barber_ready = 0 # Barber ready to cut hair
semaphore sleeping = 0 # Barber is sleeping
semaphore cutting = 0 # Barber cutting a customer's hair
def Barber():
while not finished:
wait(rw_chairs)
wait(rw_sleeping)
# If no chairs are being used
if chairs == N:
is_sleeping = true
print("Barber is sleeping!")
signal(rw_chairs) # Allow others to read/write
signal(rw_sleeping)
wait(sleeping) # Wait for customer to wake him up
signal(barber_ready) # Allow customers into the chair
print("Barber woke up!")
else:
signal(rw_signal)
chairs += 1
signal(barber_ready)
signal(rw_chairs)
# If the barber isn't done for the day, help the customer
if not finished:
print("Helping a customer")
# Wait a random amount of time
print("Finished helping a customer")
signal(cutting) # Let the customer leave after the hair cut
else:
print("Barber is done for the day!")
def Customer():
bool helped = false
while not helped:
wait(rw_chairs)
wait(rw_cutting)
if chairs == N and not is_cutting: # If the barber is free
wait(rw_sleeping)
if is_sleeping:
signal(sleeping) # Wake the barber up
is_sleeping = false
print("Customer has woken the barber up")
signal(rw_sleeping)
is_cutting = true
signal(rw_chairs)
signal(rw_cutting)
wait(barber_ready) # Wait for the barber to be ready
wait(cutting) # Wait for him to finish cutting hair
print("Customer has had his hair cut")
helped = true
else if chairs > 0:
chairs -= 1
print("Customer is waiting in a chair")
signal(rw_chairs)
signal(rw_cutting)
wait(barber_ready)
wait(cutting)
print("Customer has had his hair cut")
helped = true
else:
signal(rw_chairs)
signal(rw_office)
print("All chairs taken, will return later")
# Wait a random amount of time
print("Customer is leaving the barbershop")
如果没有死锁,使用3把椅子,我会得到以下输出:
Barber has fallen asleep
Customer is waiting in a chair
Customer is waiting in a chair
Customer is waiting in a chair
All chairs used, will return later
All chairs used, will return later
... (repeat the above line infinitely)
我很清楚,理发师没有适当地让顾客进来——但即使这样,我觉得我的结构完全错了。我认为我处理这个问题的方法是错误的,而且可能使它过于复杂
如果这里有人对如何构建一个有效的解决方案有任何建议,或者对我当前的解决方案有任何建议,我将不胜感激。或者如果我在正确的轨道上,可能是朝着正确的方向推动
谢谢 我设法让它工作起来了 鉴于我以前在这里的任何地方都没有看到过这样的问题,我会回答我自己的问题,以防其他人遇到像我这样寻求帮助的问题 我最初的方法并不是完全错误的,但是有一些小的调整需要让它正常工作。我没有使用6个信号量,而是使用了5:2控制读/写访问,3控制排队/睡眠 伪代码如下所示:
# Constants
SLEEPING = 0
AWAKE = 1
BUSY = 2
# Read/Write semaphores
Semaphore rw_chairs = 1 # Access to chairs
Semaphore rw_status = 1 # Access to barber status
# Access semaphores
Semaphore waiting = 0 # Line for waiting customers
Semaphore cutting = 0 # Semaphore to hold customer while getting hair cut
Semaphore sleeping = 0 # Semaphore for barber to sleep
int chairs = n # Available chairs to sit in
int status = AWAKE # Barber Status (could also be a boolean for sleeping)
bool finished = false # Is the program finished
def Barber():
while not finished:
wait(rw_chairs)
wait(rw_status)
# If there is nobody waiting and the barber isn't asleep
if chairs == n and status != SLEEPING:
barber = SLEEPING;
print("Barber went to sleep!")
signal(rw_status)
signal(rw_chairs)
wait(sleeping) # Go to sleep
print("Barber woke up!")
signal(waiting) # Let the next customer in
else:
signal(waiting) # Let the next customer in
chairs += 1 # Free the chair they sat in
barber = BUSY # Set the barber to busy
signal(rw_status)
signal(rw_chairs)
# Once it gets here, the barber is awake and must help someone
if not finished:
print("Barber is cutting a customer's hair")
# Cut the customer's hair
print("Barber finished cutting the customer's hair")
signal(cutting) # Release the customer so they can leave
# barber's finally done
print("Barber finished work for the day");
def Customer():
bool helped = false
print("Customer arrived at the Barber Shop!")
while not helped:
wait(rw_chairs)
wait(rw_status)
if chairs == n and status == SLEEPING:
status = AWAKE
print("Customer woke up the barber")
signal(rw_status)
signal(sleeping) # Wake up the barber
wait(waiting) # Be the next customer to get helped (happens immediately)
signal(rw_chairs)
helped = true; // This customer is being helped
else:
signal(rw_status)
if chairs > 0:
chairs -= 1 # Claim a chair
signal(rw_chairs)
print("Customer sitting in a chair")
wait(waiting) # Wait for the barber
helped = true; // This customer is being helped
else:
print("Barber Shop is busy, will return later")
signal(rw_chairs)
# Wait a while before returning
# If the customer is being helped
if helped:
print("Customer is getting a hair cut")
wait(cutting)
print("Customer is finished getting a haircut")
大体上,一旦所有客户线程都加入,它就会将finished设置为true,并唤醒可能正在睡觉的理发师以完成程序
通过这种方法,理发师和顾客都会先读取椅子,然后读取状态,然后按相反的顺序释放,以防止循环等待造成死锁