Using the Process Model

   Process Model Configuration
   Reactive Process Recycling
   Proactive Process Recycling
   Logging Process Model Events
   Enabling Web Gardens
   Section Summary

To solve this problem, ASP.NET provides an out-of-process execution model, which protects the server process from user code. It also enables you to apply heuristics to the lifetime of the process to improve the availability of your Web applications. Using asynchronous interprocess communication enables you to provide the best balance of performance, scalability, and reliability.

Process Model Configuration

Process model settings are exposed in the root configuration file for the computer, Machine.config. The configuration section is named <processModel> and is shown in the following example. The process model is enabled by default (enable="true").

<processModel
    enable="true"
    timeout="infinite"
    idleTimeout="infinite"
    shutdownTimeout="0:00:05"
    requestLimit="infinite"
    requestQueueLimit="5000"
    memoryLimit="80"
    webGarden="false"
    cpuMask="0xffffffff"
    userName=""
    password=""
    logLevel="errors"
    clientConnectedCheck="0:00:05"
/>

Reactive Process Recycling

Reactive process recycling occurs when a process is misbehaving or unable to serve requests. The process typically displays detectable symptoms, such as deadlocks, access violations, memory leaks, and so on, in order to trigger a process recycle. You can control the conditions that trigger a process restart by using the configuration settings described in the following table.

Setting	Description
requestQueueLimit	Handles deadlock conditions. The DWORD value is set to the maximum allowed number of requests in the queue, after which the worker process is considered to be misbehaving. When the number is exceeded, a new process is launched and the requests are reassigned. The default is 5000 requests.
memoryLimit	Handles memory leak conditions. The DWORD value is set to the percentage of physical memory that the worker process can consume before it is considered to be misbehaving. When that percentage is exceeded, a new process is launched and the requests are reassigned. The default is 80%.
shutdownTimeout	Specifies the amount of time the worker process has to shut itself down gracefully (string value in hr:min:sec format). When the time out expires, the ASP.NET ISAPI shuts down the worker process. The default is "00:00:05".

Proactive Process Recycling

Proactive process recycling restarts the worker process periodically even if the process is healthy. This can be a useful way to prevent denials of service due to conditions the process model is unable to detect. A process can be restarted after a specific number of requests or after a time-out period has elapsed.

Setting	Description
timeout	String value in hr:min:sec format that configures the time limit after which a new worker process will be launched to take the place of the current one. The default is infinite, a keyword indicating that the process should not be restarted.
idleTimeout	String value in hr:min:sec format that configures the amount of inactivity, after which the worker process is automatically shut down. The default is infinite, a keyword indicating that the process should not be restarted.
requestLimit	DWORD value set to the number of requests after which a new worker process will be launched to take the place of the current one. The default is infinite, a keyword indicating that the process should not be restarted.

Logging Process Model Events

The process model can write events to the Windows event log when process cycling occurs. This is controlled by the logLevel attribute in the <processModel> configuration section.

Setting	Description
logLevel	Controls that process cycling events are logged to the event log. The value can be: All: All process cycling events are logged. None: No events are logged. Errors: Only unexpected events are logged.

When a cycling event occurs, if logging is enabled for that event, the following events are written to the application event log.

Shutdown Reason	Event Log Type	Description
Unexpected	Error	The ASP.NET worker process has shut down unexpectedly.
RequestQueueLimit	Error	The ASP.NET worker process has been restarted because the request queue limit was exceeded.
RequestLimit	Information	The ASP.NET worker process has been restarted because the request limit was exceeded.
Timeout	Information	The ASP.NET worker process has been restarted because the time-out interval was met.
IdleTimeout	Information	The ASP.NET worker process has been shut down because the idle time-out interval was met.
MemoryLimitExceeded	Error	The ASP.NET worker process was restarted because the process memory limit was exceeded.

Enabling Web Gardens

The process model helps enable scalability on multiprocessor computers by distributing the work to several processes, one per CPU, each with processor affinity set to its CPU. This eliminates cross-processor lock contention and is ideal for large SMP systems. This technique is called Web gardening. The configuration settings for enabling Web gardens are listed in the following table. Note that these settings take effect only after a server is restarted. IIS must be cycled in order for this change to take place.

Setting	Description
webGarden	Controls CPU affinity. True indicates that processes should be affinitized to the corresponding CPU. The default is False.
cpuMask	Controls the number of processes and how the Web garden works. One process is launched for each CPU where the corresponding bit in the mask set to 1. When UseCPUAffinity is set to 0, the cpuMask setting only controls the number of worker processes (number of bits set to 1). The maximum-allowed number of worker processes is the number of CPUs. By default, all CPUs are enabled; the same number of worker processes is launched as there are CPUs. The default value is 0xffffffff.

Web gardening has some side effects that you should be aware of:

• If your application uses session state, it must choose an out-of-process provider (NT Service or SQL).
• Application state and application statics are per process, not per computer.
• Caching is per process, not per computer.

Section Summary

1. ASP.NET provides an out-of-process execution model, which protects the server process from user code. It also enables you to apply heuristics to the lifetime of the process to improve the overall availability of Web applications.
2. The <processModel> settings are exposed in the root configuration file for the computer's Machine.config file. The process model is enabled by default.
3. The process model supports two types of recycling: reactive and proactive. Reactive process recycling occurs when a process is misbehaving or unable to serve requests. Proactive process recycling restarts the worker process periodically, even when the process may be healthy.
4. The process model can write events to the Windows event log when process cycling occurs. This is controlled by the log-level attribute in the <processModel> configuration section.
5. The process model helps enable scalability on multiprocessor computers by distributing the work to several processes, one per CPU, each with processor affinity set to its CPU. This technique is called Web gardening.