代写ProgExchange

Task description
Introducing ProgExchange (PEX), a cutting-edge platform for computer programmers to buy and sell
high-demand components in a virtual marketplace. The need for in-person trading has been replaced
by a state-of-the-art digital marketplace, allowing for greater accessibility and faster transactions,
while providing a safe and convenient way for seasoned programmers to connect and make transactions.
As part of this assignment, you will be tasked with developing two key components of ProgExchange:
the exchange itself, which will handle all incoming orders, and an auto-trading program that executes
trades based on predefined conditions. With your expertise in systems programming, you will play
a crucial role in bringing this innovative platform to life and helping to drive the future of computer
component trading.

Some implementation details are purposefully left ambiguous; you have the freedom to decide on the
specifics yourself. Additionally this description does not define all possible behaviour that can be
exhibited by the system; some error cases are not documented. You are expected to gracefully report
and handle these errors yourself.
High Level Overview
Exchange
The purpose of the ProgExchange is to allow trading to happen in an efficient and orderly manner. It
receives orders from traders and matches them, allowing the buying and selling of computer components.
The exchange also tracks the cash balance of each trader (which starts at $0 for each trading session).
For providing such trading avenue, ProgExchange collects a 1% transaction fee on all successful
orders.
IPC
The exchange communicates with trader processes using a combination of named pipes (FIFOs) and
signals. All messages are followed by the delimiter ; and signal SIGUSR1.
All messages sent through FIFOs are highlighted in this document:
EXAMPLE;
Traders
Traders carry out their buying and selling activities by placing orders on the exchange.

Commands
The following commands may be sent from traders to the exchange:
BUY

;
SELL ;
AMEND ;
CANCEL ;
• BUY: An order to buy a product at or below the specified price, up to the specified quantity.
• SELL: An order to sell a product at the specified price, up to the specified quantity.
• AMEND: Update the quantity or price of an existing order, that has yet to be fully filled.
• CANCEL: Cancel an existing order, that has yet to be fully filled.
Data Types and Ranges
• ORDER_ID: integer, 0 - 999999 (incremental)
Order ID is unique per Trader (i.e. Trader 0 and 1 can both have their own Order ID 0). Order
IDs are not reused (with the exception of Invalid orders, which can be fixed and re-sent with
the same ID, given the next ID is not yet used).
• PRODUCT: string, alphanumeric, case sensitive, up to 16 characters
• QTY, PRICE: integer, 1 - 999999
Products
Products traded on the exchange are provided through a text file of the following structure:
n_items
Product 1
Product 2
...
Product N
For example:
2
GPU
Motherboard

Basic Example
• Trader 0 places a SELL order for 15 CPUs at $300 each
SELL 0 CPU 15 300;
• Trader 1 places a BUY order for 10 CPUs at $300 each
BUY 0 CPU 10 300;
• ProgExchange matches these orders, Trader 1 buys 10 CPUs from Trader 0 for $3,000 and pays
$30 transaction fee.
• Trader 1’s order is now fulfilled. Trader 0 has 5 CPUs remaining on the market for sale.
Implementation details
Write programs in C that implement ProgExchange as shown in the examples.
You are guaranteed not to have NULL returned from malloc() or realloc() in this context.
Your submission must be contained in the following files and produce no errors when built and run
on Ed C compiler.
• pe_common.h: Common constants and structures
• pe_exchange.c, pe_exchange.h: Part 1 (Exchange, compiles to pe_exchange)
• pe_trader.c, pe_trader.h: Part 2 (Trader, compiles to pe_trader)
• Test cases in tests directory
• README.md: Code Description
Read / write with FIFOs and/or write to stdout as instructed.
Your program output must match the exact output format shown in the examples and on Ed. You are
encouraged to submit your assignment while you are working on it, so you can obtain feedback.
You may modify any of the existing scaffold files, or make your own.
No external code outside the standard C library functions should be required.
In order to obtain full marks, your program must free all of the dynamic memory it allocates.

Milestone: Auto-Trader
To complete the milestone, you need to implement an auto-trader in pe_trader.c and pe_trader.h,
which will be tested against a reference exchange server implementation.
The logic of the auto-trader is very simple: as soon as a SELL order is available in the exchange, it
will place an opposite BUY order to attempt to buy the item.
As an example, as soon as the auto-trader receives the following message (and signal) from the exchange:
MARKET SELL CPU 2 300;
It would place the following order:
BUY CPU 2 300;
The auto-trader should gracefully disconnect and shut down if there is a BUY order with quantity
greater than or equal to 1000.
For the milestone, you may assume that for the purposes of this auto-trader, there are no other competing traders placing BUY orders.
However, signals are inherently unreliable, that is, multiple signals (perhaps from multiple autotraders) may overwrite one another and cause a race condition. In the final version, you should design
your auto-trader in such way that it is fault-tolerant, while conforming to the Exchange messaging
protocol (first write to the pipe, then signal SIGUSR1), and does not place unreasonable load on the
exchange.

Exchange: Start Up
The exchange accepts command line arguments as follows:
./pe_exchange [product file] [trader 0] [trader 1] ... [trader n]
The following example uses a product file named products.txt and trader binaries trader_a and trader_b:
./pe_exchange products.txt ./trader_a ./trader_b
Upon start up, the exchange should read the product file to find out about what it will trade. It should
then create two named pipes for each trader:
/tmp/pe_exchange_
/tmp/pe_trader_
The pe_exchange_* named pipes are for the exchange write to each trader and pe_trader_* named
pipes are for each trader to write to the exchange.
After both pipes are created for a trader, the exchange shall launch that trader binary as a new child
process, assigning it a trader ID starting from 0, in the Command Line Argument order. The trader
ID shall be passed to the trader binary as a command line argument.
For the example above, the trader binaries should be launched like so:
./trader_a 0
./trader_b 1
Upon launching each binary, the exchange and trader should attempt to connect to both named pipes.
After all binaries are launched and pipes are connected, the exchange should send each trader (lowest
trader IDs first) the following message using the pe_exchange_* named pipes; afterwards, notify each
trader using the SIGUSR1 signal.
MARKET OPEN;
Exchange: Placing Orders
Traders may place orders with the exchange by sending the appropriate commands through their
pe_trader_ named pipe. Once the whole command is written to the pipe, it shall notify
the exchange with the SIGUSR1 signal.
Once the exchange receives the SIGUSR1 signal from a trader, it would read the command from the
pe_trader_ named pipe and process the order appropriately. Depending on whether the
order was accepted (for new buy / sell orders), amended or cancelled, or if the command is invalid, it
would write one of the following messages to the pe_exchange_ named pipe and notify
the trader using the SIGUSR1 signal.

ACCEPTED ;
AMENDED ;
CANCELLED ;
INVALID;
The exchange should also message all other traders (lowest trader IDs first) using the pe_exchange_*
named pipes, and notify them using the SIGUSR1 signal, with the following message:
MARKET ;
N.B.: In case of a cancelled order, QTY = 0 and PRICE = 0.
Sample order flow
1. Trader 0 writes to pe_trader_0:
SELL 20 CPU 2 300;
2. Trader 0 sends SIGUSR1 signal to the Exchange
3. Exchange reads pe_trader_0 and adds the order to the order book
4. Exchange writes to pe_exchange_0:
ACCEPTED 20;
5. Exchange sends SIGUSR1 signal to Trader 0
6. Exchange writes to all other pe_exchange_* pipes:
MARKET SELL CPU 2 300;
7. Exchange sends SIGUSR1 signal to all other Traders.
8. All traders can read their own pe_exchange_* and places further orders if desired
Exchange: Matching Orders
The exchange should attempt to match orders once there is at least one BUY and one SELL order for
any particular product. Orders match if the price of the BUY order is larger than or equal to the price
of the SELL order. The matching price is the price of the older order. Of the two matched traders, the
exchange charges 1% transaction fee to the trader who placed the order last, rounded to the nearest
dollar (eg: $4.50 -> $5.00).
When there are multiple orders in the exchange, order matching should follow price-time priority:
• Match the highest-priced BUY order against lowest-priced SELL order

COMP2017 9017 PEX
• If there are multiple orders at the same price level, match the earliest order first
As the order matches, the exchange shall write the following message to the appropriate pe_exchange_*
pipes belonging to the matched traders, then send the SIGUSR1 signal:
FILL ;
The exchange should first sent the FILL message to the buyer of the order, then the seller. It is
possible for a single order with sufficient quantity to match against multiple existing orders in the
market. Similarly, an order could be partially filled and remain in the market if there isn’t sufficient
quantity available. Orders are removed from the market once their quantity reaches zero.
Example Scenarios
Example Orderbook Before
(type, qty, price) New Order Orderbook After
(type, qty, price) Explanation
0
SELL 2 $500
BUY 2 $450 BUY 2 $500 BUY 2 $450 The new buy order matched
against the SELL order. Both
orders are fully filled.
1
SELL 2 $501
SELL 2 $500 BUY 5 $505 BUY 1 $505 The new BUY order matched
against both SELL orders.
The SELL orders are fully
filled. The BUY order is partially filled (qty 4) and remains on the market (qty 1).
Exchange: Reporting
In addition to reading and writing to the named pipes, the exchange also needs to print a range of
messages to standard out (stdout), as per the examples later in this document. Please follow the
examples for the outputs required.
Specifically, the order book and trader positions need to be printed after each successful order, for
example:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 3; Sell levels: 1
[PEX] SELL 99 @ $511 (1 order)
[PEX] BUY 30 @ $502 (1 order)
[PEX] BUY 60 @ $501 (2 orders)
[PEX] BUY 30 @ $500 (1 order)

[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)


Here, all orders in the market are sorted from the highest to lowest price. Each unique price is calleda level, and there may be multiple orders in the same level. Positions refer to the quantity of productsowned (or owed) by each trader, which may be positive or negative after each order.
Note: Tabs (\t) are used for indentation.
Exchange: Teardown
As soon as a trader disconnects (closing their end of the pipes or process exits), your exchange shouldprint out the following message:
[PEX] Trader disconnected
It shall reject any pending or further orders from the trader but keep existing orders in the orderbook(if any).
After all traders disconnect, the exchange should print out the following message:
[PEX] Trading completed
[PEX] Exchange fees collected: $
Make sure to clean up any remaining child processes, close and delete FIFOs, and free memory beforeexiting.
Code Description
To support your implementation, you need to provide a succinct answer to each of the questions inthe file README.md. The word limit is 150 for each question.
1. Describe how your exchange works, using diagram(s) if necessary.
2. Describe your design decisions for the trader and how it’s fault-tolerant and efficient.
3. Describe your tests and how to run them.

Exchange: Example Outputs
# cat products.txt
2
GPU
Router
1 trader, 1 order
Command:
./pe_exchange products.txt ./trader_a
Orders:
Trader 0: BUY 0 GPU 30 500
Standard out:
[PEX] Starting
[PEX] Trading 2 products: GPU Router
[PEX] Created FIFO /tmp/pe_exchange_0
[PEX] Created FIFO /tmp/pe_trader_0
[PEX] Starting trader 0 (./trader_a)
[PEX] Connected to /tmp/pe_exchange_0
[PEX] Connected to /tmp/pe_trader_0
[PEX] [T0] Parsing command:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 1; Sell levels: 0
[PEX] BUY 30 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)
[PEX] Trader 0 disconnected
[PEX] Trading completed
[PEX] Exchange fees collected: $0
2 traders, 6 orders
Command:
./pe_exchange products.txt ./trader_a ./trader_b
Orders:

Trader 0: BUY 0 GPU 30 500
Trader 0: BUY 1 GPU 30 501
Trader 0: BUY 2 GPU 30 501
Trader 0: BUY 3 GPU 30 502
Trader 1: SELL 0 GPU 99 511
Trader 1: SELL 1 GPU 99 402
Standard out:
[PEX] Starting
[PEX] Trading 2 products: GPU Router
[PEX] Created FIFO /tmp/pe_exchange_0
[PEX] Created FIFO /tmp/pe_trader_0
[PEX] Starting trader 0 (./trader_a)
[PEX] Connected to /tmp/pe_exchange_0
[PEX] Connected to /tmp/pe_trader_0
[PEX] Created FIFO /tmp/pe_exchange_1
[PEX] Created FIFO /tmp/pe_trader_1
[PEX] Starting trader 1 (./trader_b)
[PEX] Connected to /tmp/pe_exchange_1
[PEX] Connected to /tmp/pe_trader_1
[PEX] [T0] Parsing command:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 1; Sell levels: 0
[PEX] BUY 30 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)
[PEX] Trader 1: GPU 0 ($0), Router 0 ($0)
[PEX] [T0] Parsing command:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 2; Sell levels: 0
[PEX] BUY 30 @ $501 (1 order)
[PEX] BUY 30 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)
[PEX] Trader 1: GPU 0 ($0), Router 0 ($0)
[PEX] [T0] Parsing command:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 2; Sell levels: 0
[PEX] BUY 60 @ $501 (2 orders)
[PEX] BUY 30 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)
[PEX] Trader 1: GPU 0 ($0), Router 0 ($0)

[PEX] [T0] Parsing command:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 3; Sell levels: 0
[PEX] BUY 30 @ $502 (1 order)
[PEX] BUY 60 @ $501 (2 orders)
[PEX] BUY 30 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)
[PEX] Trader 1: GPU 0 ($0), Router 0 ($0)
[PEX] [T1] Parsing command:
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 3; Sell levels: 1
[PEX] SELL 99 @ $511 (1 order)
[PEX] BUY 30 @ $502 (1 order)
[PEX] BUY 60 @ $501 (2 orders)
[PEX] BUY 30 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 0 ($0), Router 0 ($0)
[PEX] Trader 1: GPU 0 ($0), Router 0 ($0)
[PEX] [T1] Parsing command:
[PEX] Match: Order 3 [T0], New Order 1 [T1], value: $15060, fee: $151.
[PEX] Match: Order 1 [T0], New Order 1 [T1], value: $15030, fee: $150.
[PEX] Match: Order 2 [T0], New Order 1 [T1], value: $15030, fee: $150.
[PEX] Match: Order 0 [T0], New Order 1 [T1], value: $4500, fee: $45.
[PEX] --ORDERBOOK--
[PEX] Product: GPU; Buy levels: 1; Sell levels: 1
[PEX] SELL 99 @ $511 (1 order)
[PEX] BUY 21 @ $500 (1 order)
[PEX] Product: Router; Buy levels: 0; Sell levels: 0
[PEX] --POSITIONS--
[PEX] Trader 0: GPU 99 ($-49620), Router 0 ($0)
[PEX] Trader 1: GPU -99 ($49124), Router 0 ($0)
[PEX] Trader 0 disconnected
[PEX] Trader 1 disconnected
[PEX] Trading completed
[PEX] Exchange fees collected: $496

Compilation and Execution
Your program will be compiled by running the default rule of a make file. Upon compiling your
program should produce a two binaries: pe_exchange, pe_trader
make
./pe_exchange products.txt ./trader_a ./trader_b
Please make sure the above commands will compile and run your program. An example Makefile
has been provided in the Scaffold, but you’re encouraged to customize it to your needs. Additionally,
consider implementing the project using multiple C source files and utilizing header files.
Tests will be compiled and run using two make rules; make tests and make run_tests.
make tests
make run_tests
These rules should build any tests you need, then execute each test and report back on your correctness.
Failing to adhere to these conventions will prevent your markers from running your code and tests. In
this circumstance you will be awarded a mark of 0 for this assignment.
You are encouraged to submit multiple times, but only your last submission will be marked.
Writing your own test cases
We have provided you with some test cases but these do not test all the functionality described in
the assignment. It is important that you thoroughly test your code by writing your own test cases,
including both end-to-end (input / output) tests and unit tests using cmocka.

You should place all of your end-to-end test cases in the tests/E2E directory. Ensure that each test
case has a .out output file and optionally an .in file. We recommend that the names of your test cases
are descriptive so that you know what each is testing, e.g. buy-order.out and amend-order.out.
You should place all of your unit tests in the tests directory, under unit-tests.c (and more
files, if necessary). All unit tests must be constructed with the cmocka unit testing framework.
You should have a brief description of your tests, and how they can be run, in README.md.
Error handling
Your code should have appropriate mechanisms in place to detect and handle errors, including but not
limited to:
• NULL pointers
• Buffer overflows and underflows
• Unable to open FIFOs
• Unable to launch child processes
• Invalid or malformed commands
Restrictions
If your program does not adhere to these restrictions, your submission will receive 0.
• No Variable Length Arrays (VLAs)
• No threads (processes only)
• No excessive / 100% CPU usage when idling (eg: busy-waiting loops, active polling)
• Traders must be launched as child processes of the exchange process.
Marking
A grade for this assignment is made where there is a submission that compiles and the oral examination has been completed.
• Milestone Automated Test Cases - 5 - Passing automatic test cases.
• Final Automated Test Cases - 10 - Passing automatic test cases, a number of tests will not be
released or run until after your final submission.
– You are guaranteed that no trader will send multiple signals to the exchange such that they
would conflict, the order of signals sent to exchange program will be deterministic and
reliable.

– An order is expected to be processed within a reasonable time. e.g. Trader 0 BUY X, ->
100ms later -> Trader 0 BUY Y.
– The automated test will be checking the program functions in an implementation independent manner using the specified protocol.

Additionally marks will be deducted if:
• your program has memory leaks.
• excessive memory is used, e.g preallocation or over allocation of what is required.
• your program avoids malloc family of C functions to instantiate memory dynamically.
• your program does not use named pipes or signals for IPC.
• uses unjustifiable magic numbers.
• uses files, or mapped memory.
• any documentation part of your submission, including code comments, README files, and so
on, are not written in English.
• poor code readability will result in the deduction of marks. Your code and test cases should be
neatly divided between header and source files in appropriate directories, should be commented,
contain meaningful variable names, useful indentation, white space and functions should be
used appropriately. Please refer to this course’s style guide for more details.
Warning: Any attempts to deceive the automatic marking will result in an immediate zero for the
entire assignment. Negative marks can be assigned if you do not properly follow the assignment
description, or your code is unnecessarily or deliberately obfuscated.

Where to start
Begin with implementing the auto-trader (Milestone):
• read the full specification and make sure you understand the communication protocol.
• confirm you can open FIFOs setup by the exchange process.
• create a trader with basic functionality.
Exchange.
• confirm you can setup FIFOs and launch child processes
• confirm your processes can communicate through FIFOs and signals
• implement a simple order book for BUY / SELL orders
• check that it can handle multiple orders, identical orders and overlapping orders
Next, implement AMEND / CANCEL commands and the ability to handle multiple traders.
Next, implement the auto-trader, paying special attention to fault-tolerance and error recovery.