Glossary: promises, protocols and race conditions — DedSec Project

Promise

Precise meaning

A JavaScript value representing a pending, fulfilled or rejected asynchronous computation. A Promise can resolve later, and errors travel through rejection handlers.

Reference experiment

async function answer(){ return 42; }
answer().then(x => console.assert(x===42)).catch(console.error);

Investigate the boundary

Change answer() to throw Error and compare catch with try/await. Explain why synchronous try without await cannot catch later rejections.

Independent check

For Promise, document the expected outcome before running the sample. Change one important assumption and decide whether the failure belongs to the caller, the implementation or the environment.

Protocol

Precise meaning

An agreement specifying message format, sequencing, error responses and roles between communicating components. HTTP is a protocol; JSON alone is just one representation.

Reference experiment

GET /status HTTP/1.1
Host: example.test

# Expected success might be HTTP/1.1 200 OK

Investigate the boundary

Define request and response states for a tiny read-only status API. Test an unknown route and invalid method; explain which layer decides 404 versus 405.

Independent check

For Protocol, document the expected outcome before running the sample. Change one important assumption and decide whether the failure belongs to the caller, the implementation or the environment.

Race condition

Precise meaning

Behavior that changes when independent operations interleave in different orders. A race condition may be logical even without unsynchronized memory access.

Reference experiment

balance=10
# Two workers both read 10, calculate 3 and 4 debit independently.
# Last write wins: incorrect final balance instead of 3.

Investigate the boundary

Model two concurrent debits as a timeline, identify the read-modify-write race and fix it with a transaction or suitable synchronization.

Independent check

For Race condition, document the expected outcome before running the sample. Change one important assumption and decide whether the failure belongs to the caller, the implementation or the environment.

Recursion

Precise meaning

A function calling itself on a smaller subproblem. Correct recursion needs a base case and a measure that moves toward it; otherwise stack depth can grow without bound.

Reference experiment

def factorial(n):
    if n < 0: raise ValueError()
    if n == 0: return 1
    return n*factorial(n-1)
assert factorial(4)==24

Investigate the boundary

Trace the call frames for factorial(3), including return order. Compare with an iterative version for large n and test invalid negatives.

Independent check

For Recursion, document the expected outcome before running the sample. Change one important assumption and decide whether the failure belongs to the caller, the implementation or the environment.

Refactoring

Precise meaning

Change to internal structure while preserving externally observable behavior under a defined contract. Tests and behavior checks provide evidence; renaming alone is not sufficient validation.

Reference experiment

def total(items):
    return sum(items)
assert total([2,3])==5

Investigate the boundary

Extract a long conditional into a named function and run identical positive, empty and invalid inputs before/after. Compare outputs and exceptions.

Independent check

For Refactoring, document the expected outcome before running the sample. Change one important assumption and decide whether the failure belongs to the caller, the implementation or the environment.