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.

Worker Thread Pool Events

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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I/O Thread Events

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.

See Also

CLR ETW Events