CS378h: Honors Concurrency

Go Lab: BST Comparison

Submission Guide

Read this page first for detailed instructions about how to do this lab.

When computing the hash of a tree, we will use the following function:

  // initial hash value
  hash = 1;
  for each value in tree.in_order_traversal() {
    new_value = value + 2;
    hash = (hash * new_value + new_value) % 4222234741
  }

The given input data (simple.txt, coarse.txt, and fine.txt) is used for exploring the difference between implementations to prepare the writeup. Hidden input data will be used by the autograder to test performance and correctness of each implementation. Your program will be tested for each step of the algorithm. Flags are used to select different implementations by the autograder. Make sure your program accept the exact flag(s) for a particular implementation as detailed below.

You should put your main Go program in ~/workspace. If you do not complete the optional implementation in step 2.2, name your main go program BST.go. Instead, name it BST_opt.go.

1. Computation of Hash of Each Tree

1.1 Flags

The following flag controls the number of goroutines to compute the hash of each BST

• -hash-workers=<number of hash workers to hash BSTs>: spawn hash-workers goroutines to iterate the available BSTs to compute the hash.

When -hash-workers is set to 1, you do not have to spawn any goroutines. You can simply compute the hash of all trees in the main thread. When -hash-workers is the only flag provided, your program should only compute the hash of each BST without performing the rest two steps (identification of hash duplicates and tree comparison). This is for the autograder to collect performance for this step only.

1.2 Output

For any number of hash workers, your program should output the time it takes to compute the hashes of all BSTs. Make sure that the time is measured after all goroutines are synchronized. The output should have the following form

hashTime: xxx

Do not include tree construction time.

1.3 Testing

Your program will be tested for the following numbers of hash workers

(1,2,4,8,16,N)

where N is the total number of BSTs.

2. Computation of Hash Groups

2.1 Flags

The following flag controls the synchronization mechanism for hash-workers goroutines to update the map

• -data-workers=<number of workers to update the map>: there will be data-workers goroutines trying to update the map.

Your program should select the proper implementation according to the following combinations of flags:

1. -hash-workers=1 -data-workers=1: This is the sequential implementation. Your program can compute the hash of all BSTs and update the map in the main thread.
2. -hash-workers=i -data-workers=1(i>1): This implementation spawns i goroutines to compute the hashes of input BSTs. Each goroutine sends its (hash, BST ID) pair(s) to a central manager goroutine using the channel. The central manager updates the map.
3. -hash-workers=i -data-workers=i(i>1): This implementation spawns i goroutines to compute the hashes of input BSTs. Each goroutine updates the map individually after acquiring the mutex.

The following combination of flags are for the optional implementation:

• -hash-workers=i -data-workers=j(i>j>1): This implementation spawns i goroutines to compute the hashes of input BSTs. Then j goroutines are updating the map.
  • It is up to you how the hash workers are communicating with the j data workers. You can use a semaphore so that j of the i hash workers can update the map. Or you can use j central managers to collect (hash, BST ID) pairs from each hash worker via j channels.
  • When j goroutines try to update the map, make sure each hash entry is not updated by more than two threads at the same time.

2.2 Output

For each implementation, your program should output the elapsed time as well as the hash groups in the following form:

hashGroupTime: xxxxxx
hash0: id00 id01 ..
hash1: id10 id11 ..
..

hashi is the ith hash value and idi0, idi1,... are tree ids that have the same hash value hashi. Ids are separated by spaces. Do not print hash groups that have only one tree. Note that hashGroupTime includes the time for hash computations.

Do not show any output from the tree comparison if -comp-workers is not specified.

2.3 Correctness

The autograder will compare the output hash groups with the sample. Both hash values and corresponding tree ids should match with the sample. Therefore, make sure you are using the SHA256 hash algorithm to compute the hash of each tree, which is represented by its in order traverse.

2.4 Performance

The autograder will run each implementation 10 times to obtain an average elapsed time as the performance. Possible i values include 2, 4, 8, 16, N, where N is the number of BSTs in the input file. For the optional implementation, possible j values include 2, 4, 8, 16.

3. Tree Comparison

3.1 Flags

The following flag controls the number of goroutines to do tree comparisons.

• -comp-workers=<number of workers to do the comparisons>: there will be comp-workers goroutines to compare pairs of trees.

-comp-workers=1 corresponds to the sequential implementation, in which your program can simply do tree comparisons in the main thread.

3.2 Output

Your program should measure how much time it takes to compare trees (compareTreeTime) and output the tree groups in the following form:

compareTreeTime: yyyyyy
group 0: id00 id01 ...
group 1: id10 id11 ...
..

Do not print groups that have only one tree.

It is ok that your program also outputs the hash groups from the previous step.

3.3 Correctness

The autograder will compare the tree groups with the sample. Group ids do not have to match.

3.4 Performance

The autograder will execute each implementation 10 times and compute an average elapsed time as the performance of tree comparison. Possible comp-workers values include 1,2,4,8,16.