Advanced Troubleshooting with Debug Diagnostics on IIS 6

Advanced Troubleshooting with Debug Diagnostics on IIS 6 Chris Adams Program Manager IIS Product Unit Microsoft Corporation

Agenda Debug Diagnostics 1. 0 Dig into crash scenarios Understanding hangs Investigating memory leaks Session Summary

Debug Diagnostics 1. 0 “Core” pieces of Debug. Diag Understanding “Rules” Using Debug. Diag’s User Interface

Core pieces of Debug Diag 3 pieces make up Debug Diag 1. 0 Service Host (also called Controller) User Interface Dbg. Svc. exe Dbg. Host. exe Debug. Diag. exe

Core pieces of Debug Diag The Service – Dbg. Svc. exe Service is multipurposed Interacts with the Debugger Host Allows: Service required to attach invasively to process To run from Terminal Services Dbg. Svc. exe To register the service: C: Debug. Diag> Dbg. Svc /service To start the service: C: Debug. Diag> net start Dbg. Svc To stop the service C: Debug. Diag> net stop Dbg. Svc Unregister the service C: Debug. Diag> Dbg. Svc /unregserver

Core pieces of Debug Diag The Host – Dbg. Host. exe Host Where the Dbg. Eng. dll instance is loaded Exposes 3 classes Dbg. Svc. exe Attach Dbg. Host. exe Dbg. Control: Attach/Detach from processes or open/analyze a memory dump Dbg. Obj: Collect process or memory dump information Manager: Mainly to output analysis data to the report file

Core pieces of Debug Diag The User Interface – Debug. Diag. exe User Interface designed to simplify: Rule creation View processess Initiate analysis of memory dumps Add analysis scripts Change properties for Debug Diag Debug. Diag. exe Control Scripts Dbg. Host. exe

Crash Scenarios Background of crashes Using Debug. Diag to quickly identify root cause of crashes

Background: Exceptions What is an exception? How do applications cause exceptions What is a “handled” exception? Unhandled exceptions need debugging and resolution Access Violation: C 0005 Breakpoint Exception: 8000 0003 Stack Overflow: C 000 00 FD C++ exception: E 06 D 7363 Managed exception: E 0434 F 4 D Invalid Handle: C 0008

Background: Heap (2) What is a heap? Heap is a data structure Heap Corruption: Certain rules must be followed when using the heap When rules are violated, heap corruption occurs Heap corruption crashes Code that corrupts heap is usually not the ones impacted

Debugging Crashes with Debug Diagnostics: Crash Rule Chris Adams Program Manager IIS Product Unit

Hang Scenarios Investigating theory of “process hangs” Using Debug. Diag to debug “process hangs”

Theory of “Process Hangs” What is a process? Memory boundary for execution of code Allocated by Operating System done by calling Create. Process or Create. Process. As. User API Processes do not execute code Contains a minimum of 1 thread What is a thread? An independent sequence of instructions executing within a process

Theory of “Process Hangs” Thread implications on applications The level of concurrency (virtual) is dictated by the number of threads Real concurrency is dictated by the number of execution units 1 processor = one or more execution units What are common thread pools for IIS? ATQ thread pool ASP. NET thread pool

Runaway Threads A runaway thread is a thread stuck in a infinite (or near) loop Performing a task that is consuming CPU Either by design or because of error conditions Runaway thread is taking CPU resources away from other threads Often takes away from good threads Causes performance degradation for server

Defining a Blocked Thread A thread that isn’t using any CPU resources Waiting on database calls to return Waiting on web service calls to return Waiting on a socket/network call to return Waiting on a lock Thread 3 Thread IIS Thread 4 1 SQL

Locks and Deadlocks What is a lock? A synchronization mechanism to protect resources from being corrupted due to simultaneous access by multiple threads Why do developers use locks? Protecting data Protecting other resources that are not memory based Impact on applications if locks are poorly implemented Causes threads to block Can cause deadlock situations when using multiple locks in the application Process hangs when no threads are available

Debugging Deadlocks and Process Hangs with Debug. Diag: Hang Rule Chris Adams Program Manager IIS Product Unit

Looking into Leaks… What is a leak? Types of Leaks Debugging a Leak with Debug Diagnostics

Leak Scenarios (2) Why are leaks difficult to identify and resolve? Server applications often cache memory allocations The allocations are long term These applications, to outsiders, look to have memory leaks There are many other caches Using Performance Monitor and seeing memory growth does not equal a memory leak

Leak Scenarios (3) What are short-term allocations? Memory expensive applications use “spike” allocations but are destroyed immediately after request (not long- sustaining) These are not Memory Leaks

Leak Scenarios (4) Difference between cache and memory leaks? Memory leaks are caused by unbounded allocations Cache memory usage rises quickly, but tops out after application is stabilized

Nailing a Memory Leak in a Web Application using Debug. Diag: Memory Rule Chris Adams Program Manager IIS Product Unit

Session Summary Debugging Live Web Applications without downtime is challenging Crashes cause processes to terminate due to unhandled exceptions Hangs are caused due to race conditions, lock contention, network blocking, database blocking, infinite loops and deadlocks Leaks are caused by the failure to release memory allocated beyond typical short term allocations and caching Debug Diagnostics has an extensibility model that allows it to successfully capture and analyze common debugging scenarios to determine the root cause

Debug Diagnostics 1. 0 web resources http: //www. iisdiagnostics. com