queue_priority

Queue with priorities (test task) my testing task for Sperasoft
Task 1: Need to design and implement a priority queue in C, and provide a test application which demonstrates that the queue is working. A few requirements:

1. Priority values are integers
2. Priority queues should be thread-safe
3. Priority queues should generate "High water mark"/"Low water mark" events.
4. Test application should create at least two threads writing into the queue and at least two threads reading from the queue.
5. For anything which isn't mentioned in these requirements, you can make a choice yourself.
6. Test application should come with some instructions for compiling it.

Review of project:

How application look inside: 1. #define COUNT_WRITERS 1 #define COUNT_READERS 1

is describe the minimum set of consume and customer threads. They may sets are different integer value (but not negative) for stress test.

2. About High water mark"/"Low water mark": heap-structure execute the callback functions in different cases for interconnection with main code.

• send "Low water mark" event when is remove last element, and counter size equals to zero.
• send "High water mark" event when counter of elements are equal to max size queue and next incoming elements will be ignored and not puts to queue.

Above events are not change any internal logic in this application, but look like logical that we must handles this events and such situation and make some actions - such as stop reading, writing, or may increase queue size (reallocation of internal bufffer are not supported), stop threads (or kill them).

3. Some additional tools - handler user command from keyboard - it is made for test application in different condition - we may change count of consumer-customer threads #define MAX_ADDS_THREADS 10 Above define describe maximum counter of writes and reads threads (for every category - 10 reads && 10 writes). How it use:

  q- add new readers thread;
  w - add new writers thread;
  a - kill readers thread
  s - kill writers thread

(need to press "Enter" after every command)

it builds with GCC 5.4.0 on Ubuntu 16.04(x86), use pthread library and CMake (min. 2.8).

How build:

Go to the directory with source

mkdir build
cd  build
cmake ..
make

For start:

./SperasoftPriorityQueue 

Example of output:

Writer insert item: 5 - Task 5,  3030383424 
Queue: 0 5 2 1 0 
	 Reader(3059489600) get item: prior(5), Task 5, 3030383424 
Queue: 0 2 0 1 
	 Reader(3051096896) get item: prior(2), Task 2, 3076275008 
Writer insert item: 8 - Task 8,  3076275008

What we see above: consumer-thread send element with priority 5, additional field - "Task5" and 3030383424(thread ID). That values only for illustration that we may to send additional information. After that we see "Queue: 0 5 2 1 0 " - it from customer-thread - it internal view of queue - they sorted by priory. Next customer-thread get element from queue with max priority. In output - we see current thread id, priority, and additional info. It is also for clarity, not means some usefull info.

If see many of "LOW_WATER_MARK received" - increase count of writers - press 'w' and 'Enter', or decrease count of readers - press 'a' If see many of "HIGH_WATER_MARK received" - incread count of readers - press 'a' and 'Enter', or decrease count of writers - press 's'