FAQ
Hi everyone!
I've been playing around with golang.org/x/mobile/audio on my desktop pc
but I've experienced an unexpected side effect.
please note that the example I'm pasting reproduces my issue but *I don't
think the issue is strictly related to audio/OpenAL, it looks more like
something with the runtime/GC.*
but enough with theories, here are the facts: I'm running on amd64 linux,
go 1.4.2 64b.

basically audio pkg was not working for me at all, so I went and looked at
the underlying code and OpenAL wrapper and managed to write a working
example.
then I went back to the audio implementation and tried to understand what
was the difference.
here is the code, this code *works* as expected, it plays a sin wave at
1500Hz for a couple of seconds.
(I've intentionally stripped all the error checking to make it as concise
as possible for pasting, nothing odd is going on with return values)

package main

import (
"fmt"
"golang.org/x/mobile/audio/al"
"math"
)

func main() {
samplesPerSecond := int64(44100)
frequency := int64(1500)

device := al.Open("")
context := device.CreateContext(nil)
al.MakeContextCurrent(context)

buffers := al.GenBuffers(1)
bytes := make([]byte, 100000)
FillBufferMono8(bytes, samplesPerSecond, frequency)
buffers[0].BufferData(uint32(0x1100), bytes, int32(samplesPerSecond))

sources := al.GenSources(1)
sources[0].QueueBuffers(buffers)
al.PlaySources(sources[0])

waiter := make(chan int)
<-waiter
fmt.Println("you won't see this")

al.DeleteSources(sources[0])
al.DeleteBuffers(buffers)
context.Destroy() // Comment this line
device.Close()
}

func FillBufferMono8(buffer []byte, samplesPerSecond int64, frequency
int64) {
bufferLength := len(buffer)
for i := int64(0); i < int64(bufferLength); i++ {
sampleIndex := i
sinResult := math.Sin(math.Pi * 2 * (float64(sampleIndex%samplesPerSecond)
/ float64(samplesPerSecond)) * float64(frequency))
sample := byte(255 * 0.5 * (1.0 + sinResult))
buffer[i] = sample
}
}


fact is, if you comment the line
context.Destroy() // Comment this line
it stops working (no sound played) and behaves exactly as the audio pkg,
giving this output:
AL lib: (WW) FreeContext: (0x8efb20) Deleting 1 Source(s)

as you can see that line comes after a never signaled chan, so it is, for
all practical purposes, unreachable.
the fact that it does or does not exists changes the behaviour of the
program.
Am I missing something? I see the OpenAL wrapper directly interacts with C,
are there some side effect I'm not aware of?

--
You received this message because you are subscribed to the Google Groups "golang-nuts" group.
To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.

Search Discussions

  • David Crawshaw at Apr 29, 2015 at 1:43 am
    +jbd

    A guess: when you comment out the line the context value is no longer
    reachable. So the garbage collector collects it and the finalizer
    cleans up the underlying machinery and so the sound stops. To test
    this theory: try making the object a global variable.

    If this is what's going on, it's probably a bug. The al package should
    be pinning the object if there are resources associated with it that
    are still live.
    On Tue, Apr 28, 2015 at 4:22 PM, wrote:
    Hi everyone!
    I've been playing around with golang.org/x/mobile/audio on my desktop pc but
    I've experienced an unexpected side effect.
    please note that the example I'm pasting reproduces my issue but I don't
    think the issue is strictly related to audio/OpenAL, it looks more like
    something with the runtime/GC.
    but enough with theories, here are the facts: I'm running on amd64 linux, go
    1.4.2 64b.

    basically audio pkg was not working for me at all, so I went and looked at
    the underlying code and OpenAL wrapper and managed to write a working
    example.
    then I went back to the audio implementation and tried to understand what
    was the difference.
    here is the code, this code works as expected, it plays a sin wave at 1500Hz
    for a couple of seconds.
    (I've intentionally stripped all the error checking to make it as concise as
    possible for pasting, nothing odd is going on with return values)

    package main

    import (
    "fmt"
    "golang.org/x/mobile/audio/al"
    "math"
    )

    func main() {
    samplesPerSecond := int64(44100)
    frequency := int64(1500)

    device := al.Open("")
    context := device.CreateContext(nil)
    al.MakeContextCurrent(context)

    buffers := al.GenBuffers(1)
    bytes := make([]byte, 100000)
    FillBufferMono8(bytes, samplesPerSecond, frequency)
    buffers[0].BufferData(uint32(0x1100), bytes, int32(samplesPerSecond))

    sources := al.GenSources(1)
    sources[0].QueueBuffers(buffers)
    al.PlaySources(sources[0])

    waiter := make(chan int)
    <-waiter
    fmt.Println("you won't see this")

    al.DeleteSources(sources[0])
    al.DeleteBuffers(buffers)
    context.Destroy() // Comment this line
    device.Close()
    }

    func FillBufferMono8(buffer []byte, samplesPerSecond int64, frequency int64)
    {
    bufferLength := len(buffer)
    for i := int64(0); i < int64(bufferLength); i++ {
    sampleIndex := i
    sinResult := math.Sin(math.Pi * 2 * (float64(sampleIndex%samplesPerSecond) /
    float64(samplesPerSecond)) * float64(frequency))
    sample := byte(255 * 0.5 * (1.0 + sinResult))
    buffer[i] = sample
    }
    }


    fact is, if you comment the line
    context.Destroy() // Comment this line
    it stops working (no sound played) and behaves exactly as the audio pkg,
    giving this output:
    AL lib: (WW) FreeContext: (0x8efb20) Deleting 1 Source(s)

    as you can see that line comes after a never signaled chan, so it is, for
    all practical purposes, unreachable.
    the fact that it does or does not exists changes the behaviour of the
    program.
    Am I missing something? I see the OpenAL wrapper directly interacts with C,
    are there some side effect I'm not aware of?

    --
    You received this message because you are subscribed to the Google Groups
    "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an
    email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
    --
    You received this message because you are subscribed to the Google Groups "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
  • Daniele Colla at Apr 29, 2015 at 1:28 pm
    thanks David, you are very likely right
    I was thinking about something having to do with the GC, and looking at the
    sources I completely missed the device.CreateContext function adding a
    finalizer to the Context object

    but is the GC supposed to be this aggressive? context isn't even out of
    scope yet. it looks a bit error prone..
    anyway, how would you handle that in the original code?

    (ref https://github.com/golang/mobile/blob/master/audio/audio.go)

    --
    You received this message because you are subscribed to the Google Groups "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
  • David Crawshaw at Apr 29, 2015 at 1:49 pm
    The garbage collector can clean up any unreachable memory. You're in
    the scope, but you have no further uses of context.

    But your code should work. If a context is current
    (al.MakeContextCurrent) and there are valid sources being played
    (al.PlaySources), then nothing should be cleaned up automatically. The
    al package should be pinning the object and it's not.

    If you wouldn't mind, please file an issue and assign it to jbd.
    On Wed, Apr 29, 2015 at 9:28 AM, Daniele Colla wrote:
    thanks David, you are very likely right
    I was thinking about something having to do with the GC, and looking at the
    sources I completely missed the device.CreateContext function adding a
    finalizer to the Context object

    but is the GC supposed to be this aggressive? context isn't even out of
    scope yet. it looks a bit error prone..
    anyway, how would you handle that in the original code?

    (ref https://github.com/golang/mobile/blob/master/audio/audio.go)

    --
    You received this message because you are subscribed to the Google Groups
    "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an
    email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
    --
    You received this message because you are subscribed to the Google Groups "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
  • Burcu Dogan at Apr 29, 2015 at 5:22 pm
    Daniele, could you file an issue? It's clearly a bug. We should either
    pin the context or reconsider our finalizer strategy.
    On Wed, Apr 29, 2015 at 6:49 AM, David Crawshaw wrote:
    The garbage collector can clean up any unreachable memory. You're in
    the scope, but you have no further uses of context.

    But your code should work. If a context is current
    (al.MakeContextCurrent) and there are valid sources being played
    (al.PlaySources), then nothing should be cleaned up automatically. The
    al package should be pinning the object and it's not.

    If you wouldn't mind, please file an issue and assign it to jbd.
    On Wed, Apr 29, 2015 at 9:28 AM, Daniele Colla wrote:
    thanks David, you are very likely right
    I was thinking about something having to do with the GC, and looking at the
    sources I completely missed the device.CreateContext function adding a
    finalizer to the Context object

    but is the GC supposed to be this aggressive? context isn't even out of
    scope yet. it looks a bit error prone..
    anyway, how would you handle that in the original code?

    (ref https://github.com/golang/mobile/blob/master/audio/audio.go)

    --
    You received this message because you are subscribed to the Google Groups
    "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an
    email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
    --
    You received this message because you are subscribed to the Google Groups "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
  • Daniele Colla at Apr 29, 2015 at 6:25 pm
    Sure, as soon as I get home

    --
    You received this message because you are subscribed to the Google Groups "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.
  • Daniele Colla at Apr 30, 2015 at 12:47 pm
    issue filed, not sure I can assign it though

    Il giorno mercoledì 29 aprile 2015 20:25:18 UTC+2, Daniele Colla ha scritto:
    Sure, as soon as I get home
    --
    You received this message because you are subscribed to the Google Groups "golang-nuts" group.
    To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscribe@googlegroups.com.
    For more options, visit https://groups.google.com/d/optout.

Related Discussions

Discussion Navigation
viewthread | post
Discussion Overview
groupgolang-nuts @
categoriesgo
postedApr 28, '15 at 8:39p
activeApr 30, '15 at 12:47p
posts7
users3
websitegolang.org

People

Translate

site design / logo © 2022 Grokbase