DistributedCurrency

Implemented Totally Ordered multicast using Lamport's Logical Clocks. Replica consistency was maintained on 3 Virtual Machines using active replication protocol. Multithread and Socket Programming techniques were used for implementation. Completely in JAVA

Distributed control of currency exchange value

The idea is to have the processes on the VMs share a currency value as speci􀄞d by the pair of rates (sell rate, buy rate). The processes can access the currency value simultaneously. As the same 􀆟me, concurrent update operations are allowed on the value of currency. An operation that occurs at a process is contained in a message that is delivered to other processes as well as the node itself. Each process has two threads: a worker thread and dispatcher thread. The process generates random rates changes (􀑐x, 􀑐y) at random intervals and sends them to all the processes including itself. The dispatcher thread waits for updates (􀑐x, 􀑐y) from other replicas. Upon receiving a message, it inserts the message in its local queue and multicasts an acknowledgement to the other processes. The local queue containing messages is ordered according to the timestamps of the messages. That is, the earlier the timestamp, the closer the message is to the head of the queue. Requirements Your program should be running on the VM instances given to you. As the underlying transport protocol, TCP is to be used to communicate between processes. You will therefore need multithread and socket programming skills. Below are useful links for this homework in Java. We will accept only Java solu􀆟ons for this homework. Socket Programming Tutorial: h􀆩p://java.sun.com/docs/books/tutorial/networking/sockets/index.html Multi-threading Tutorial: h􀆩p://java.sun.com/docs/books/tutorial/essential/concurrency/index.html For details on multithread servers, please refer to page 77 in the textbook. Processes are assumed to be numbered (Pn) in the order of the last digit of the IP address of the virtual machine that the process is residing in. The process numbers range from 0 to 2. Thus the processes are named P0, P1, and P2. For example, P0: 192.168.0.2 (the lowest) P1: 192.168.0.3 P2: 192.168.0.4 (the highest)

Each process is assumed to have an endpoint location consisting of the IP address and the port. For example, the endpoint of the process P0 would be 192.168.0.2:9999 if the port number is 9999. Also, each process has a list of the endpoints for all the processes (P0, P1, and P2) in the network including itself. To do this, your program should read a file named “info.txt” that contains a list of addresses and connect them one by one as described in the deployment phase 1 below. The file name should be EXACTLY the same as “info.txt” in lower case. The lines of the file contain the IP address and port of a process as: [ip address] [port] The content of the file “info.txt” would be the following: 192.168.0.2 9999 192.168.0.3 9999 192.168.0.4 9999 Again, use the first 4 digits of your UFID as the port number. The details of the implementation are described below. Currency The currency value is specified by a pair of rates (sell rate, buy rate). It is initially set to (100, 100). Rate changes (i.e., the “deltas”) Δx and Δy are in the range [-80, 80]. A process can update the rate by delta (Δx, Δy). Update operation: new pair of rates (x’, y’) = current pair of rates (x, y) + delta (Δx, Δy) That is, (x’, y’) = (x + Δx, y + Δy) where x and y are integer type and the range of Δx and Δy is [-80, 80] including -80 and 80. (For simplicity, we allow negative rates in this homework.) Message A message contains a type, process id, and payload as shown below. You may add more types if necessary.

• Type: UPDATE, ACK o UPDATE: indicates the rate changes (Δx, Δy) o ACK: acknowledges the UPDATE message has been received
• Payload: o If type is UPDATE then the payload contains the process id of the message sender and the pair of rates (x, y) of the currency o If type is ACK then the payload contains the process id of the message sender and the timestamp of the message. Queue A process has its own local queue to store messages. A message in the queue is inserted in the order of its timestamp. It is removed from the queue only when it is acknowledged by all the other processes.

Clock counter Processes maintain a Lamport clock at a constant rate (ticks/sec). However, the clock rates are di􀄫erent for each process. The clock increases by the clock rate every second. In addition, it increases by 1 for every event (sending/receiving/delivering message) as in the textbook pages 246-247. For example, if P0, P1, and P2 have clock counter unit of 2, 3, and 1, respectively, then the clocks tick as follows. Note that the process id is attached to low-order end of time separated by a decimal point to break the tie. P0’s clock: 2 ticks/sec 0.0 2.0 4.0 … P1’s clock: 3 ticks/sec 0.1 3.1 6.1 … P2’s clock: 1 tick/sec 0.2 1.2 2.2 … Command line The main program name is Curren cy. The program should accept the process id and the number of update operations to be performed. $java Currency [Process id] [Number of operations] [clock rate] e.g., java 0 30 4 If you run 30 update operations for each process, you would end up with 90 (30 * 3) update operations performed.

Currency Deployment Phase 1: Connection setup All the processes on the VMs are started. You will need to have the processes wait until the other processes are up. When a process starts, it establishes TCP connections to the processes with lower process ID. In this case, P0 starts P1 starts and connects to P0 P2 starts and connects to P0 and P1. Phase 2: Running phase Once all the processes are running and connected to each other, each process starts update the currency value by randomly generating rate changes (Δx, Δy) of the value pair (x, y) at every interval period. The interval is chosen also randomly between 0 to 1000 milliseconds (1 second) excluding 0. A process sends the update (Δx, Δy) to all the processes including itself. It also accepts incoming messages from other processes and performs the operations in the messages. Upon receiving an UPDATE message, the process multicasts acknowledgement (ACK) messages to others. The process is allowed to update the value of its currency ONLY after it receives acknowledgements from all the processes. Note that the order of updates performed could be different from what is actually done in real-time, but all the processes see the updates in the same order (total order). Also, since there are local objects shared by multiple threads, you need to consider synchronization of accesses to the objects within a process. Phase 3: Termination phase After the number of iterations given, all the processes are terminated gracefully. Note that a process terminates only after all the messages are delivered and its local queue is empty. Also, the process is allowed to terminate after it confirms that others have finished their job (no more messages to send AND have delivered all the messages). In order to do this, they need to exchange finishing messages. Termination conditions

1. All the messages are delivered.
2. Local queue is empty
3. Other processes finish Logging Your program is required to create a log file in which all the events regarding connections and messages are written with the timestamps. The log files are named log0, log1, and log2 with the number being the corresponding process id. Process connection When a process is connected to other process, write something like the following into the log file: P0 is connected to P1 (192.168.0.3). When a process is connected from other process, write something like the following into the log file: P1 is connected from P0 (192.168.0.2).

When a process has 􀄮nished its job, write something like the following into the log file: P2 finished. P0 finished. P1 finished. When all the processes have finished, write something like the following into the log file: All finished. P2 is terminating… Message When a message is delivered, the currency is set to a new value pair and this event is wri􀆩en into a line in the log file. The line has three columns which represent the local time, process id of the message sender, timestamp, and the current rates of currency separated by a white space as shown below. column1 column2 column3 [ localtime ] [ operation number : local counter ] description of the event … [ month/day hour:minute:second ] [ OPnum : Cclock ] description of the event … where operation number and local counter start from 1. The exact format is: [ MM/DD hh:mm:ss ] [OPnum : Cclock ] Currency value is set to (x,y) by (􀑐x, 􀑐y). An example of the log 􀄮le of the process P1 would be: IMPORTANT: Your log file format MUST be the same as the above format. Otherwise, you will not get credit.