CLR ETW Providers

The common language runtime (CLR) has two providers: the runtime provider and the rundown provider.

The runtime provider raises events, depending on which keywords (categories of events) are enabled. For example, you can collect loader events by enabling the LoaderKeyword keyword.

Event tracking for Windows (ETW) events are logged into a file that has an .etl extension, which can later be post-processed in comma-separated value (.csv) files as needed. For information about how to convert the .etl file to a .csv file, see Controlling .NET Framework Logging.

The runtime provider is the main CLR ETW provider.

The CLR runtime provider GUID is e13c0d23-ccbc-4e12-931b-d9cc2eee27e4.

For examples of how to log and view CLR ETW events by using commonly available tools, see Controlling .NET Framework Logging.

In addition to using keywords such as LoaderKeyword, you may have to enable keywords for logging events that may be raised too frequently. The StartEnumerationKeyword and the EndEnumerationKeyword keywords enable these events and are summarized in CLR ETW Keywords and Levels.

The rundown provider must be turned on for certain special-purpose uses. However, for a majority of users, the runtime provider should suffice.

The CLR rundown provider GUID is A669021C-C450-4609-A035-5AF59AF4DF18.

Normally, ETW logging is enabled before a process launches, and the logging is turned off after the process exits. However, if ETW logging is turned on while the process is executing, additional information is needed about the process. For example, for symbol resolution you have to log method events for methods that were already loaded before logging was turned on.

The DCStart and DCEnd events capture the state of the process when data collection was started and stopped. (State refers to information at a high level, including the methods that were already just-in-time (JIT) compiled and assemblies that were loaded.) These two events can provide information about what has already happened in the process; for example, which methods were JIT- compiled, and so on.

Only the events with DC, DCStart, DCEnd, or DCInit in their names are raised under the rundown provider. Additionally, these events are raised only under the rundown provider.

In addition to the event keyword filters, the rundown provider also supports the StartRundownKeyword and EndRundownKeyword keywords to provide targeted filtering.

A start rundown is triggered when logging under the rundown provider is enabled with the StartRundownKeyword keyword. This causes the DCStart event to be raised, and captures the state of the system. Before the start of the enumeration, the DCStartInit event is raised. At the end of the enumeration, the DCStartComplete event is raised to notify the controller that data collection terminated normally.

An end rundown is triggered when logging under the rundown provider is enabled with the EndRundownKeyword keyword. End rundown stops profiling on a process that continues to execute. The DCEnd events capture the state of the system when profiling is stopped.

Before the start of the enumeration, the DCEndInit event is raised. At the end of the enumeration, the DCEndComplete event is raised to notify the consumer that data collection terminated normally. Start rundown and end rundown are primarily used for managed symbol resolution. Start rundown can provide address range information for methods that were already JIT-compiled before the profiling session was started. End rundown can provide address range information for all methods that have been JIT-compiled when profiling is about to be turned off.

End rundown does not happen automatically when a profiling session is stopped. Instead, a tool that is seeking to perform managed symbol resolution has to explicitly invoke a CLR rundown provider session with the EndRundownKeyword keyword enabled, just before profiling is stopped.

Although either start rundown or end rundown can provide method address range information for managed symbol resolution, we recommend that you use the EndRundownKeyword keyword (which supplies DCEnd events) instead of the StartRundownKeyword keyword (which supplies DCStart events). Using StartRundownKeyword causes the rundown to happen during the profiling session, which may disturb the profiled scenario.

The following example demonstrates how to use the CLR rundown provider in a way that allows symbol resolution of managed processes with minimal impact, regardless of whether the processes start or end inside or outside the profiled window.

  1. Turn on ETW logging by using the CLR runtime provider:

    xperf -start clr -on e13c0d23-ccbc-4e12-931b-d9cc2eee27e4:0x1CCBD:0x5 -f clr1.etl    
    

    The log will be saved to the clr1.etl file.

  2. To stop profiling while the process continues to execute, start the rundown provider to capture the DCEnd events:

    xperf -start clrRundown -on A669021C-C450-4609-A035-5AF59AF4DF18:0xB8:0x5 -f clr2.etl    
    

    This enables the collection of DCEnd events to start a rundown session. You may need to wait 30 to 60 seconds for all events to be collected. The log will be saved to the clr1.et2 file.

  3. Turn off all ETW profiling:

    xperf -stop clrRundown 
    xperf -stop clr
    
  4. Merge the profiles to create one log file:

    xperf -merge -d clr1.etl clr2.etl merged.etl
    

    The merged.etl file will contain the events from the runtime and the rundown provider sessions.

A tool can execute steps 2 and 3 (starting a rundown session and then terminating profiling) instead of immediately turning off profiling when a user requests profiling to be stopped. A tool can also execute step 4.

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