pipeline causes memory leak when used with async generator

[matthieusieben]

• Version: v15.6.0
• Platform: Darwin MBPM.local 20.2.0 Darwin Kernel Version 20.2.0: Wed Dec 2 20:39:59 PST 2020; root:xnu-7195.60.75~1/RELEASE_X86_64 x86_64
• Subsystem: stream.pipeline

What steps will reproduce the bug?

• Launch the following script with node --inspect-brk --expose-gc test.js
• Open a chrome inspector and play until the first debugger statement is reached (will auto pause).
• Start an Allocation timeline profiling
• Start running the script again (F8)
• When reaching the second debugger, stop the profiling
• Notice 10 references to the Passthrough are still in memory

const { PassThrough, pipeline } = require('stream')
const { promisify } = require('util')
const nextTick = promisify(process.nextTick)

const consume = async (it) => {
  for await (const _item of it) continue
}

async function* genItems(count) {
  const source = async function* () {
    // Generate way too many items
    while (true) {
      await nextTick() // simulate async
      yield { foo: 'bar' }
    }
  }

  const duplex = new PassThrough({ objectMode: true })

  const stream = pipeline(source, duplex, (err) => {
    console.log('done', err) // err.code === ERR_STREAM_PREMATURE_CLOSE
  })

  for await (const item of stream) {
    yield item
    if (--count <= 0) break
  }
}

const test = async () => {
  const stream = genItems(2)
  await consume(stream)
}

const main = async () => {
  debugger // <== Start memory allocation timeline profiling now
  for (let i = 0; i < 10; i++) await test()
  global.gc()
  debugger // <== Stop memory profiling now
}

main()

How often does it reproduce? Is there a required condition?

Only occurs when breaking a loop on the async generator.

What is the expected behavior?

It should be possible to use a stream pipeline as an async generator without having memory leaks.

What do you see instead?

When profiling, references to the Passthrough still appear in memory:

Additional information

Might be linked to #35452

[matthieusieben]

so the "leak" is probably linked to the console keeping a ref (through the error).

[meixg]

With this #35452 solved, I tried on the master branch and this problem has gone.