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Improving threading safety for telemetry #250

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Improving threading safety for telemetry #250

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c016afc
Improving threading safety for telemetry
MichaelGHSeg Dec 3, 2024
c03f7a0
Another attempt without synchronized, tests need work
MichaelGHSeg Dec 4, 2024
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59 changes: 34 additions & 25 deletions core/src/main/java/com/segment/analytics/kotlin/core/Telemetry.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@ import java.util.concurrent.ConcurrentLinkedQueue
import java.util.concurrent.Executors
import kotlin.math.min
import kotlin.math.roundToInt
import java.util.concurrent.atomic.AtomicBoolean

class MetricsRequestFactory : RequestFactory() {
override fun upload(apiHost: String): HttpURLConnection {
Expand Down Expand Up @@ -76,7 +77,14 @@ object Telemetry: Subscriber {
var host: String = Constants.DEFAULT_API_HOST
// 1.0 is 100%, will get set by Segment setting before start()
// Values are adjusted by the sampleRate on send
var sampleRate: Double = 1.0
@Volatile private var _sampleRate: Double = 1.0
var sampleRate: Double
get() = _sampleRate
set(value) {
synchronized(this) {
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we should try our best to avoid using synchronized since our API is coroutine-based. people could use our API inside a coroutine which causes a suspend function to block.

_sampleRate = value
}
}
var flushTimer: Int = 30 * 1000 // 30s
var httpClient: HTTPClient = HTTPClient("", MetricsRequestFactory())
var sendWriteKeyOnError: Boolean = true
Expand All @@ -93,9 +101,9 @@ object Telemetry: Subscriber {

private val queue = ConcurrentLinkedQueue<RemoteMetric>()
private var queueBytes = 0
private var started = false
private var started = AtomicBoolean(false)
private var rateLimitEndTime: Long = 0
private var flushFirstError = true
private var flushFirstError = AtomicBoolean(true)
private val exceptionHandler = CoroutineExceptionHandler { _, t ->
errorHandler?.let {
it( Exception(
Expand All @@ -113,8 +121,8 @@ object Telemetry: Subscriber {
* Called automatically when Telemetry.enable is set to true and when configuration data is received from Segment.
*/
fun start() {
if (!enable || started || sampleRate == 0.0) return
started = true
if (!enable || started.get() || sampleRate == 0.0) return
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if we need atomic on started, likely we need it on enable

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Started could maybe get away without as well, but enable will in most cases not ever change and there are several checks where if it happens to pass by one check, it will avoid sending later. But mainly I thought it not worth changing the interface and documentation just yet, since enable is the only exposed API.

started.set(true)

// Everything queued was sampled at default 100%, downsample adjustment and send will adjust values
if (Math.random() > sampleRate) {
Expand All @@ -124,7 +132,7 @@ object Telemetry: Subscriber {
telemetryJob = telemetryScope.launch(telemetryDispatcher) {
while (isActive) {
if (!enable) {
started = false
started.set(false)
return@launch
}
try {
Expand All @@ -148,7 +156,7 @@ object Telemetry: Subscriber {
fun reset() {
telemetryJob?.cancel()
resetQueue()
started = false
started.set(false)
rateLimitEndTime = 0
}

Expand Down Expand Up @@ -202,8 +210,8 @@ object Telemetry: Subscriber {

addRemoteMetric(metric, filteredTags, log=logData)

if(flushFirstError) {
flushFirstError = false
if(flushFirstError.get()) {
flushFirstError.set(false)
flush()
}
}
Expand All @@ -218,7 +226,6 @@ object Telemetry: Subscriber {

try {
send()
queueBytes = 0
} catch (error: Throwable) {
errorHandler?.invoke(error)
sampleRate = 0.0
Expand All @@ -227,16 +234,14 @@ object Telemetry: Subscriber {

private fun send() {
if (sampleRate == 0.0) return
var queueCount = queue.size
// Reset queue data size counter since all current queue items will be removed
queueBytes = 0
val sendQueue = mutableListOf<RemoteMetric>()
while (queueCount-- > 0 && !queue.isEmpty()) {
val m = queue.poll()
if(m != null) {
m.value = (m.value / sampleRate).roundToInt()
sendQueue.add(m)
}
val sendQueue: MutableList<RemoteMetric>
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instead of snapshot the whole queue, snapshot the size of the queue and dequeue just for that size should work and that avoid of using synchronized

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That's what the code was doing originally, can probably just make the queueBytes atomic and leave it at that.

synchronized(queue) {
sendQueue = queue.toMutableList()
queue.clear()
queueBytes = 0
}
sendQueue.forEach { m ->
m.value = (m.value / sampleRate).roundToInt()
}
try {
// Json.encodeToString by default does not include default values
Expand Down Expand Up @@ -309,9 +314,11 @@ object Telemetry: Subscriber {
tags = fullTags
)
val newMetricSize = newMetric.toString().toByteArray().size
if (queueBytes + newMetricSize <= maxQueueBytes) {
queue.add(newMetric)
queueBytes += newMetricSize
synchronized(queue) {
if (queueBytes + newMetricSize <= maxQueueBytes) {
queue.add(newMetric)
queueBytes += newMetricSize
}
}
}

Expand All @@ -338,7 +345,9 @@ object Telemetry: Subscriber {
}

private fun resetQueue() {
queue.clear()
queueBytes = 0
synchronized(queue) {
queue.clear()
queueBytes = 0
}
}
}
12 changes: 7 additions & 5 deletions core/src/test/kotlin/com/segment/analytics/kotlin/core/TelemetryTest.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -10,13 +10,15 @@ import java.util.concurrent.ConcurrentLinkedQueue
import java.util.concurrent.CountDownLatch
import java.util.concurrent.Executors
import java.util.concurrent.TimeUnit
import java.util.concurrent.atomic.AtomicBoolean
import kotlin.random.Random

class TelemetryTest {
fun TelemetryResetFlushFirstError() {
val field: Field = Telemetry::class.java.getDeclaredField("flushFirstError")
field.isAccessible = true
field.set(true, true)
val atomicBoolean = field.get(Telemetry) as AtomicBoolean
atomicBoolean.set(true)
}
fun TelemetryQueueSize(): Int {
val queueField: Field = Telemetry::class.java.getDeclaredField("queue")
Expand All @@ -29,11 +31,11 @@ class TelemetryTest {
queueBytesField.isAccessible = true
return queueBytesField.get(Telemetry) as Int
}
var TelemetryStarted: Boolean
var TelemetryStarted: AtomicBoolean
get() {
val startedField: Field = Telemetry::class.java.getDeclaredField("started")
startedField.isAccessible = true
return startedField.get(Telemetry) as Boolean
return startedField.get(Telemetry) as AtomicBoolean
}
set(value) {
val startedField: Field = Telemetry::class.java.getDeclaredField("started")
Expand Down Expand Up @@ -78,11 +80,11 @@ class TelemetryTest {
Telemetry.sampleRate = 0.0
Telemetry.enable = true
Telemetry.start()
assertEquals(false, TelemetryStarted)
assertEquals(false, TelemetryStarted.get())

Telemetry.sampleRate = 1.0
Telemetry.start()
assertEquals(true, TelemetryStarted)
assertEquals(true, TelemetryStarted.get())
assertEquals(0,errors.size)
}

Expand Down
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