Design a multi-threaded synchronous log writer

Problem

Design a log writer component that is called from multiple application threads and writes logs to a single file on disk.

Requirements:

• Callers can log concurrently: log(message) may be invoked by many threads.
• Writes must be synchronous/durable : once log() returns, the message must be persisted such that it survives a process crash (assume you must fsync /flush).
• Preserve a well-defined ordering (e.g., FIFO based on call time, or per-thread order—state your choice).
• High throughput: avoid doing an fsync per message if possible.

Tasks

• Propose an implementation approach (data structures, threading model).
• Explain how you ensure durability, ordering, and performance.
• Discuss failure modes (disk full, partial writes, crash during write) and how to handle them.