在 Python 中模拟抢占式 M/M/1 队列时出现问题

Question

下面显示了我的代码，它模拟了具有两种到达类型的 M/M/1 抢占式队列，其中第一种类型的优先级高于第二种类型。但是，我不知道为什么在我的代码中抢先规则没有按应有的方式工作。 我的意思是在抢占队列中，例如，如果类型 2 的作业正在接收服务并且类型 1 的作业到达，则服务器中断类型 2 作业的服务并开始类型 1 作业的服务。但是，一旦类型 1 作业的服务完成，它应该 继续中断的类型 2 作业的服务。

在我的代码中，如果工作类型 2 正在接受服务并且工作类型 1 到达，那么工作类型 2 会立即永久离开系统。我想知道您能否告诉我为什么会发生这种情况以及如何解决？

非常感谢您提前付出的时间和精力。

import random
import simpy

rn_seed = 10
t1_interval_arrivals = 20.0
t2_interval_arrivals = 1
t1_interval_service = 5
t2_interval_service = 20


def type_1_generator(env, interval, server):
    i = 0
    while True:
        c = job(env, "type_1"+" #"+ str(i), "type_1", server, t1_interval_service)
        env.process(c)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)
        i +=1
        
def type_2_generator(env, interval, server):
    i = 0
    while True:
        c = job(env, "type_2"+" #"+str(i), "type_2", server, t2_interval_service)
        env.process(c)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)
        i +=1


def job(env, name, typ , server, sr_interval):

    arrive = env.now
    print("Job", name, "Arrived at: ",arrive)
    service_interval = random.expovariate(1.0 / sr_interval)
    print("Job", name, "Service time: ",service_interval)
    if typ == "type_1":
        while service_interval:
            with server.request(priority=1) as req:
                yield req  
                yield env.timeout(service_interval)
                service_interval = 0
                print("Job", name, "Left system at: ",env.now)
    elif typ == "type_2":
        while service_interval:
            try:
                start = env.now 
                with server.request(priority=2) as req:
                    yield req  
                    yield env.timeout(service_interval)
                    service_interval = 0
                    print("Job", name, "Left system at: ",env.now)
            except simpy.Interrupt:
                print("Job", name, "Is interrupted at: ",env.now)
                service_interval -= env.now - start
                print("Job", name, "Remaining service: ",env.now)
            print("Job", name, "Left system at ",env.now)
            
        


# Setup and start the simulation
random.seed(rn_seed)
env = simpy.Environment()

# Start processes and run
server = simpy.PreemptiveResource(env, capacity=1)
env.process(type_1_generator(env, t1_interval_arrivals, server))
env.process(type_2_generator(env, t2_interval_arrivals, server))
env.run()

以下是结果示例：

Job type_2 #1 Arrived at:  0.5601717881563535
Job type_2 #1 Service time:  34.69876113045603
Job type_1 #1 Arrived at:  16.94474499667717
Job type_1 #1 Service time:  0.22635015810062187
Job type_2 #1 Is interrupted at:  16.94474499667717
Job type_2 #1 Remaining service:  18.31418792193521
Job type_2 #1 Left system at  16.94474499667717
Job type_1 #1 Left system at:  17.17109515477779

在上面的结果中，您可以看到一旦“Job type_1 #1”到达 16.94，服务器中断了“Job type_2 #1”的服务，该作业的剩余服务时间为 18.31。但是，一旦服务器完成了“Job type_1 #1”，它就永远不会继续为“Job type_2 #1”提供服务。事实上，当“Job type_1 #1”到达时，“Job type_2 #1”立即离开了系统。这清楚地表明了我的代码有什么问题。为什么“Job type_2 #1”立即离开系统，而服务器不再继续为该作业提供服务？

Answer 1

我对您的代码进行了一些更改。需要注意的是，当您重新提交对资源的请求时，它会被放在队列的末尾。所以我给中断的二类工作比新的二类工作更高的优先级。第一类作业仍然具有最高优先级。我还添加了一些打印语句。

import random
import simpy

rn_seed = 10
t1_interval_arrivals = 20.0
t2_interval_arrivals = 1
t1_interval_service = 5
t2_interval_service = 20

# use for unique id across all jobs
i = 0

def type_1_generator(env, interval, server):
    
    global i

    while i < 6:
        c = job(env, "type_1"+" #"+ str(i), "type_1", server, t1_interval_service)
        i +=1
        env.process(c)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)
        
def type_2_generator(env, interval, server):
    global i

    while i < 4:
        c = job(env, "type_2"+" #"+str(i), "type_2", server, t2_interval_service)
        i +=1
        env.process(c)
        t = random.expovariate(1.0 / interval)
        yield env.timeout(t)


def job(env, name, typ , server, sr_interval):
    """
    use three priorites so interuped jobs can
    take precendence over type 2 jobs that have 
    not started yet

    job priorities are:
    type 1: 1
    type 2: 3
    interupted type 2: 2
    """

    arrive = env.now
    print("Job", name, "Arrived at: ",arrive)
    service_interval = random.expovariate(1.0 / sr_interval)
    print("Job", name, "Service time: ",service_interval)
    if typ == "type_1":
        while service_interval:
            with server.request(priority=1) as req:
                yield req  
                print("Job", name, "seized resource at: ",env.now)
                yield env.timeout(service_interval)
                service_interval = 0
            print("Job", name, "released resource at: ",env.now)
        print("Job", name, "finished at: ",env.now)
    elif typ == "type_2":
        priority=3
        while service_interval:
            try:
                with server.request(priority=priority) as req:
                    yield req
                    start = env.now
                    if priority == 3:
                        print("Job", name, "seized resource at: ",env.now) 
                    else:
                        print("Job", name, "resumed with resource at: ",env.now)
                    yield env.timeout(service_interval)
                    service_interval = 0
                print("Job", name, "released resource at: ",env.now)
            except simpy.Interrupt:
                # up priority to take precenance of not started jobs
                priority=2
                print("Job", name, "Is interrupted at: ",env.now)
                service_interval -= env.now - start
                print("Job", name, "Remaining service: ",service_interval)
        print("Job", name, "finished ",env.now)
            
        


# Setup and start the simulation
random.seed(rn_seed)
env = simpy.Environment()

# Start processes and run
server = simpy.PreemptiveResource(env, capacity=1)
env.process(type_1_generator(env, t1_interval_arrivals, server))
env.process(type_2_generator(env, t2_interval_arrivals, server))
env.run()