编程编写银行家算法模拟程序

银行家算法是操作系统中避免死锁的典型算法，下面是一个简单的Python实现：

# 定义银行家算法类
class BankerAlgorithm:
    def __init__(self, available, max_need, allocation):
        self.available = available  # 可用资源
        self.max_need = max_need  # 进程最大需求
        self.allocation = allocation  # 进程已分配资源
        self.need = []  # 进程还需要资源
        self.work = available  # 工作向量
        self.finish = [False] * len(allocation)  # 进程是否完成标志
        self.safe_sequence = []  # 安全序列

        # 计算进程还需要的资源
        for i in range(len(max_need)):
            self.need.append([max_need[i][j] - allocation[i][j] for j in range(len(max_need[i]))])

    # 判断是否存在安全序列
    def is_safe(self):
        while False in self.finish:
            flag = False
            for i in range(len(self.need)):
                if not self.finish[i] and self.need[i] <= self.work:
                    self.work = [self.work[j] + self.allocation[i][j] for j in range(len(self.work))]
                    self.finish[i] = True
                    self.safe_sequence.append(i)
                    flag = True
            if not flag:
                return False
        return True

    # 分配资源
    def allocate(self, process, request):
        if request <= self.need[process] and request <= self.available:
            self.available = [self.available[i] - request[i] for i in range(len(request))]
            self.allocation[process] = [self.allocation[process][i] + request[i] for i in range(len(request))]
            self.need[process] = [self.need[process][i] - request[i] for i in range(len(request))]
            if self.is_safe():
                return True
            else:
                self.available = [self.available[i] + request[i] for i in range(len(request))]
                self.allocation[process] = [self.allocation[process][i] - request[i] for i in range(len(request))]
                self.need[process] = [self.need[process][i] + request[i] for i in range(len(request))]
                return False
        else:
            return False

    # 显示当前时刻各进程的资源分配情况
    def show_allocation(self):
        print("Allocation:")
        for i in range(len(self.allocation)):
            print("Process", i, ":", self.allocation[i])
        print("")

    # 将有关请求和相应决定的列表输出到一个文件中
    def output_to_file(self, filename):
        with open(filename, "w") as f:
            f.write("Allocation:\n")
            for i in range(len(self.allocation)):
                f.write("Process " + str(i) + ": " + str(self.allocation[i]) + "\n")
            f.write("\n")
            f.write("Max Need:\n")
            for i in range(len(self.max_need)):
                f.write("Process " + str(i) + ": " + str(self.max_need[i]) + "\n")
            f.write("\n")
            f.write("Need:\n")
            for i in range(len(self.need)):
                f.write("Process " + str(i) + ": " + str(self.need[i]) + "\n")
            f.write("\n")
            f.write("Available:\n")
            f.write(str(self.available) + "\n")
            f.write("\n")
            f.write("Safe Sequence:\n")
            f.write(str(self.safe_sequence) + "\n")

使用示例：

# 测试
if __name__ == "__main__":
    available = [3, 3, 2]
    max_need = [[7, 5, 3], [3, 2, 2], [9, 0, 2], [2, 2, 2], [4, 3, 3]]
    allocation = [[0, 1, 0], [2, 0, 0], [3, 0, 2], [2, 1, 1], [0, 0, 2]]
    banker = BankerAlgorithm(available, max_need, allocation)
    banker.show_allocation()
    banker.output_to_file("output.txt")

    # 请求资源
    process = 1
    request = [1, 0, 2]
    if banker.allocate(process, request):
        print("Allocate success!")
        banker.show_allocation()
        banker.output_to_file("output.txt")
    else:
        print("Allocate failed!")