Overview

The Building H2O problem is a classic synchronization challenge in concurrent programming. The main challenge is to ensure that two hydrogen threads and one oxygen thread are properly synchronized so that they can form a water molecule, H2O, without violating the given constraints. This scenario highlights the difficulty of coordinating multiple threads to achieve a specific sequence or grouping, making sure that they interleave in a way that leads to the correct result. It mirrors real-world situations where resources (in this case, threads) must be combined in the right proportions to achieve the desired outcome.

Pseudocode

Initialize:
    semaphore oxygen = 0
    semaphore hydrogen = 0
    mutex lock

Procedure releaseOxygen():
    lock.acquire()                # Acquire lock to ensure atomic operations
    oxygen += 1                   # Increment oxygen count
    if oxygen >= 1 and hydrogen >= 2:  # Check for available threads to form a water molecule
        oxygen -= 1               # Decrement oxygen count
        hydrogen -= 2             # Decrement hydrogen count by 2
        barrier.passOxygen()      # Allow oxygen thread to pass the barrier
        barrier.passHydrogen()    # Allow two hydrogen threads to pass the barrier
        barrier.passHydrogen()
    lock.release()               # Release lock

Procedure releaseHydrogen():
    lock.acquire()                # Acquire lock to ensure atomic operations
    hydrogen += 1                 # Increment hydrogen count
    if oxygen >= 1 and hydrogen >= 2:  # Check for available threads to form a water molecule
        oxygen -= 1               # Decrement oxygen count
        hydrogen -= 2             # Decrement hydrogen count by 2
        barrier.passOxygen()      # Allow oxygen thread to pass the barrier
        barrier.passHydrogen()    # Allow two hydrogen threads to pass the barrier
        barrier.passHydrogen()
    lock.release()               # Release lock

Note:

• The pseudocode uses semaphores and a mutex to synchronize the threads.
• The barrier.passOxygen() and barrier.passHydrogen() methods are conceptual and represent the action of the respective threads passing through the barrier and forming the water molecule.
• The actual implementation might require more specific functions or methods depending on the programming language or environment used.