Java并发编程：原理、实践与挑战

### Java并发编程：原理、实践与挑战 #### 1. 银行家算法实现 银行家算法实现部分包含了注册、获取、释放和注销进程等操作，以下是具体代码： ```ada protected body Avoiding_Deadlock is procedure register (proc_id : in Process_Id; claim : in Inventory) is begin system.exposure(proc_id).claim := claim; is_registered(proc_id) := true; end register; entry acquire (for proc_id in Process_Id) ( res_id : Resource_Id; amount : Positive) when proc_id = next_contender is begin -- Grab the resource and update the system state: take_out_loan(proc_id, res_id, amount); -- Return if the result is deadlock-free: if cannot_deadlock then -- Progress the round-robin of contenders: choose_next_contender(is_ready and is_registered); return; end if; -- Abandon the attempt, restore the system state, and wait for a change: give_back_loan(proc_id, res_id, amount); is_ready(proc_id) := false; -- Progress the round-robin of contenders: choose_next_contender(is_ready and is_registered); -- Put the client back in the entry queue: requeue acquire (proc_id); end acquire; procedure relinquish (proc_id : in Process_Id; res_id : in Resource_Id; amount : in Positive) is begin give_back_loan(proc_id, res_id, amount); -- Make all waiting processes eligible to compete: is_ready := all_processes; -- Progress the round-robin of contenders: choose_next_contender(is_registered); end relinquish; procedure deregister (proc_id : in Process_Id) is begin system.exposure(proc_id).claim := none; is_registered(proc_id) := false; if is_registered /= no_processes then -- Progress the round-robin of contenders, in case process proc_id -- was next_contender: choose_next_contender(is_ready and is_registered); else -- No processes remain in contention, so set the system back to its -- initial state: is_ready := all_processes; next_contender := Process_Id'first; return; end if; end deregister; end Avoiding_Deadlock; end Banker; ``` 使用银行家算法的示例代码如下： ```ada package Types is type Process_Name is (process1, process2); type Resource_Base is (nil_id, floppy, dvd, modem); subtype Resource_Name is Resource_Base range floppy .. modem; type Stock is array (Resource_Name) of Integer; wealth : constant Stock := (1, 1, 1); end Types; use Types; package Manager is new Banker( Process_Id => Process_Name, Resource_Id => Resource_Name, Inventory => Stock, capital => wealth, no_resource => nil_id); use Manager; procedure trouble (res1, res2 : in Resource_Name; proc_id : in Process_Name) is begin Avoiding_Deadlock.register(proc_id, (floppy => 1, dvd => 0, modem => 1)); Avoiding_Deadlock.acquire(proc_id) (res1, 1); Avoiding_Deadlock.acquire(proc_id) (res2, 1); -- . . . here is the critical section Avoiding_Deadlock.relinquish(proc_id, res2, 1); Avoiding_Deadlock.relinquish(proc_id, res1, 1); Avoiding_Deadlock.deregister(proc_id); end; ``` #### 2. Java线程的创建与终止 Java线程是对象，创建和终止线程有以下特点： - **创建**：Java提供了`Thread`类和`Runnable`接口。线程类必须是`Thread`的子类或实现`Runnable`接口，且要定义自己的`run`方法。使用`new`分配器创建线程对象，调用`start()`方法激活线程，该方法会调用`run`方法。 - **终止**：线程的`run`方法返回时，线程正常终止。 - **守护线程**：线程可以以守护线程状态创建。当所有非守护线程终止时，运行时环境会直接杀死所有守护线程，这可能导致正在执行关键操作（如更新文件）的守护线程被杀死，存在安全风险。 - **等待线程终止**：`join()`方法可以让一个线程等待另一个线程终止。 - **中断机制**：每个线程有一个布尔型的中断状态，`interrupt()`方法通常将线程的中断状态设为`true`，但如果线程在`wait`、`sle