Fix Division by Zero Error in FairQueueing Class When m_active is Zero

[fales1488]

netmq/src/NetMQ/Core/Patterns/Utils/FairQueueing.cs

Line 125 in 97da3b4

m_current = (m_current + 1) % m_active;

Description

There is a potential DivideByZeroException in the FairQueueing class of NetMQ when all pipes become deactivated (m_active becomes zero). This exception occurs specifically in the RecvPipe method during the modulo operation used for round-robin scheduling of the pipes.

Steps to Reproduce

1. Create a scenario where all pipes are systematically deactivated, setting m_active to zero.
2. Continue to receive messages or perform operations that lead to the modulo operation (m_current = (m_current + 1) % m_active).

Expected Behavior

The system should handle situations where m_active is zero without throwing a DivideByZeroException, possibly by skipping the modulo operation when no active pipes are available.

Actual Behavior

The system throws a DivideByZeroException when trying to perform the modulo operation with m_active set to zero due to all pipes being deactivated.

Proposed Solution

To prevent this issue, the modulo operation in the RecvPipe method should be conditionally performed only when m_active is greater than zero. Here is the suggested change:

if (!m_more)
    m_current = m_active > 0 ? (m_current + 1) % m_active : 0;