One disadvantage of implementing Semaphore in terms of TSemaphore is that STM transactions may be retried in an arbitrary order, so a Semaphore implemented this way does not provide a guarantee that earlier attempts to acquire a permit will succeed before later attempts when a permit becomes available. We can fix this by implementing Semaphore directly. In addition, this implementation is faster.

[info] Benchmark                                (fibers)  (ops)   Mode  Cnt    Score   Error  Units
[info] SemaphoreBenchmark.semaphoreContention         10   1000  thrpt   15  189.984 ± 0.524  ops/s
[info] SemaphoreBenchmark.tsemaphoreContention        10   1000  thrpt   15   82.308 ± 0.715  ops/s