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Thread Pool ETW Events

These events collect information about worker and I/O threads.

There are two groups of thread pool events:

  • Worker thread pool events, which provide information about how an application uses the thread pool, and the effect of workloads on concurrency control.

  • I/O thread pool events, which provide information about I/O threads that are created, retired, unretired, or terminated in the thread pool.

These events relate to the runtime's worker thread pool and provide notifications for thread events (for example, when a thread is created or stopped). The worker thread pool uses an adaptive algorithm for concurrency control, where the number of threads is calculated based on the measured throughput. Worker thread pool events can be used to understand how an application is using the thread pool, and the effect that certain workloads may have on concurrency control.

ThreadPoolWorkerThreadStart and ThreadPoolWorkerThreadStop

The following table shows the keyword and level for these events. (For more information, see CLR ETW Keywords and Levels.)

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Raised when

ThreadPoolWorkerThreadStart

50

A worker thread is created.

ThreadPoolWorkerThreadStop

51

A worker thread is stopped.

ThreadPoolWorkerThreadRetirementStart

52

A worker thread retires.

ThreadPoolWorkerThreadRetirementStop

53

A retired worker thread becomes active again.

The following table shows the event data.

Field name

Data type

Description

ActiveWorkerThreadCount

win:UInt32

Number of worker threads available to process work, including those that are already processing work.

RetiredWorkerThreadCount

win:UInt32

Number of worker threads that are not available to process work, but that are being held in reserve in case more threads are needed later.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

ThreadPoolWorkerThreadAdjustment

These thread pool events provide information for understanding and debugging the behavior of the thread injection (concurrency control) algorithm. The information is used internally by the worker thread pool.

ThreadPoolWorkerThreadAdjustmentSample

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Description

ThreadPoolWorkerThreadAdjustmentSample

54

Refers to the collection of information for one sample; that is, a measurement of throughput with a certain concurrency level, in an instant of time.

The following table shows the event data.

Field name

Data type

Description

Throughput

win:Double

Number of completions per unit of time.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

ThreadPoolWorkerThreadAdjustmentAdjustment

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Description

ThreadPoolWorkerThreadAdjustmentAdjustment

55

Records a change in control, when the thread injection (hill-climbing) algorithm determines that a change in concurrency level is in place.

The following table shows the event data.

Field name

Data type

Description

AverageThroughput

win:Double

Average throughput of a sample of measurements.

NewWorkerThreadCount

win:UInt32

New number of active worker threads.

Reason

win:UInt32

Reason for the adjustment.

0x00 - Warmup.

0x01 - Initializing.

0x02 - Random move.

0x03 - Climbing move.

0x04 - Change point.

0x05 - Stabilizing.

0x06 - Starvation.

0x07 - Thread timed out.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

ThreadPoolWorkerThreadAdjustmentStats

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Description

ThreadPoolWorkerThreadAdjustmentStats

56

Gathers data on the thread pool.

The following table shows the event data.

Field name

Data type

Description

Duration

win:Double

Amount of time, in seconds, during which these statistics were collected.

Throughput

win:Double

Average number of completions per second during this interval.

ThreadWave

win:Double

Reserved for internal use.

ThroughputWave

win:Double

Reserved for internal use.

ThroughputErrorEstimate

win:Double

Reserved for internal use.

AverageThroughputErrorEstimate

win:Double

Reserved for internal use.

ThroughputRatio

win:Double

The relative improvement in throughput caused by variations in active worker thread count during this interval.

Confidence

win:Double

A measure of the validity of the ThroughputRatio field.

NewcontrolSetting

win:Double

The number of active worker threads that will serve as the baseline for future variations in active thread count.

NewThreadWaveMagnitude

Win:UInt16

The magnitude of future variations in active thread count.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

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These thread pool events occur for threads in the I/O thread pool (completion ports), which is asynchronous.

IOThreadCreate_V1

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Raised when

IOThreadCreate_V1

44

An I/O thread is created in the thread pool.

The following table shows the event data.

Field name

Data type

Description

Count

win:UInt64

Number of I/O threads, including the newly created thread.

NumRetired

win:UInt64

Number of retired worker threads.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

IOThreadRetire_V1

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Raised when

IOThreadRetire_V1

46

An I/O thread becomes a retirement candidate.

The following table shows the event data.

Field name

Data type

Description

Count

win:UInt64

Number of I/O threads remaining in the thread pool.

NumRetired

win:UInt64

Number of retired I/O threads.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

IOThreadUnretire_V1

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Raised when

IOThreadUnretire_V1

47

An I/O thread is unretired because of I/O that arrives within a waiting period after the thread becomes a retirement candidate.

The following table shows the event data.

Field name

Data type

Description

Count

win:UInt64

Number of I/O threads in the thread pool, including this one.

NumRetired

win:UInt64

Number of retired I/O threads.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

IOThreadTerminate

The following table shows the keyword and level.

Keyword for raising the event

Level

ThreadingKeyword (0x10000)

Informational (4)

The following table shows the event information.

Event

Event ID

Raised when

IOThreadTerminate

45

An I/O thread is created in the thread pool.

The following table shows the event data.

Field name

Data type

Description

Count

win:UInt64

Number of I/O threads remaining in the thread pool.

NumRetired

win:UInt64

Number of retired I/O threads.

ClrInstanceID

Win:UInt16

Unique ID for the instance of CLR or CoreCLR.

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