Null driver

-class null is SBK’s idle, pending-operation, and timeout test driver. It does not access an external storage system.

The default writer does not complete an operation. It returns an incomplete CompletableFuture with the configured timeout, which lets tests verify:

periodic reporting when a window contains no completed records;
idle ElasticWait behavior;
shutdown while an operation is pending;
future timeout and error propagation.

The reader sleeps for the configured timeout and then returns null. Normal timed shutdown can interrupt that sleep.

Options

Option	Default	Meaning
`-n`	`0`	When greater than zero, execute an empty loop with this iteration bound and then complete the write synchronously. At zero, return an incomplete future.
`-timeout`	`2147483647` ms	Timeout applied to the pending writer future and sleep duration used by the reader.

The empty -n loop is only a control-flow workload. A JIT compiler may optimize it, so it is not a calibrated CPU-delay mechanism and should not be used for latency claims.

Idle reporting example

This run should print periodic zero-record windows and then stop at the configured duration:

./build/install/sbk/bin/sbk -class null -writers 1 -size 1024 -seconds 15

Synchronous control-flow example

Setting -n above zero makes each write complete synchronously:

./build/install/sbk/bin/sbk \
  -class null -writers 1 -size 1024 -records 1000 -n 100

This can smoke-test completed-operation control flow, but it is not the recommended queue-performance workload.

Null versus PerlBench

Both drivers are synthetic, but they deliberately exercise opposite states:

Property	`Null`	`PerlBench`
Default write	Remains pending	Completes immediately
Read	Sleeps, then returns `null`	Immediately returns a reusable payload
Expected default result	Idle windows with zero completed records	High-rate completed records and latency samples
Primary purpose	Idle reporting, timeout, interruption, and shutdown behavior	End-to-end SBK/PerL throughput, allocation, and timestamp-queue comparison
Suitable for `-mpscqueue` A/B performance tests	No	Yes

They should not be merged: the distinction between “no completion” and “completion as fast as possible” is the behavior each driver exists to test.

Null-driver results are not storage results and should not be compared with durable backend operations. Use -class null -help for current defaults.