Draft JEP: Efficient Stack Walking API (original) (raw)

Jeremy Manson jeremymanson at google.com
Mon Jul 7 16:55:49 UTC 2014

Hey folks,

I don't know if Mandy's draft JEP has gotten any love, but this is something that has (in the past) been a major CPU cycle consumer for us, and we've had to invent / reinvent many wheels to fix it internally, so we'd love to see a principled solution.

A couple of notes:

We added a CallerFinder API that basically looks like this:

// Finds the caller of the invoking method in the current stack that isn't in one of the excluded classes public static StackTraceElement findCaller(Class<?>... excludedClasses);

// Finds the first caller of a given class public static StackTraceElement findCallerOf(Class<?>... classesToFind);

This isn't the ideal API (it is more the one that happened to be convenient when we threw together the class), but it gets the vast majority of use cases.

  1. Even with a super-efficient stack walker, anyone who uses the java.util.logging framework pervasively is going to see a lot of CPU cycles consumed by determining the caller. We've had a lot of luck minimizing this by using a bytecode rewriter to change callers of log(msg) to log(sourceClass, sourceMethod, msg). This is almost certainly something that could be done (even in a principled way!) by the VM; improvements to CPU usage in such apps have been dramatic.

Jeremy

On Sun, Mar 30, 2014 at 4:02 PM, Mandy Chung <mandy.chung at oracle.com> wrote:

Below is a draft JEP we are considering submitting for JDK 9.

Mandy ---------------------------- Title: Efficient API for Stack Walking Goal ---- Define a standard API for stack walking that will be efficient and performant. Non-goal -------- It is not a goal for this API be easy to use via Reflection for example use in code that is compiled for an older JDK. Motivation ---------- There is no standard API to obtain information about the caller's class and traverse the execution stack in a performant way. Existing libraries and frameworks such as Log4j and Groovy have to resort to using the JDK internal API sun.reflect.Reflection.getCallerClass(int depth). This JEP proposes to define a standard API for stack walking that will be efficient and performant and also enable the implementation up level the stack walk machinery from the VM to Java and replaces the current mechanism of Throwable.fillInStackTrace._ _Description_ _-----------_ _There is no standard API to traverse certain frames on the execution_ _stack efficiently and access the Class instance of each frame._ _There are APIs that allow to access the stack trace information:_ _- Throwable.getStackTrace()andThread.getStackTrace()that returns_ _an array ofStackTraceElementwhich contains the classname_ _and method name of a stack trace._ _-SecurityManager.getClassContext()which is a protected method_ _such that onlySecurityManagersubclass can access the class_ _context._ _These APIs require the VM to eagerly capture a snapshot of the entire_ _stack trace and returns the information representing the entire stack._ _There is no other way to avoid the cost to examine all frames if_ _the caller is only interested in the top few frames on the stack._ _BothThrowable.getStackTrace()andThread.getStackTrace()methods_ _return an array ofStackTraceElementthat contains the classname and_ _method name of a stack frame but theClassinstance._ _In fact, for applications interested in the entire stack, the specification_ _allows VM implementation to omit some frames in the stack for performance._ _In other words,Thread.getStackTrace()may return a partial stack trace._ _These APIs do not satisfy the use cases that currently depend on_ _thegetCallerClass(int depth) method or its performance overhead_ _is intolerable. The use cases include:_ _- JDK caller-sensitive APIs look up its immediate caller's class_ _which will be used to determine the behavior of the API. For example_ _Class.forName(String classname) and_ _ResourceBundle.getBundle(String rbname) methods use the immediate_ _caller's class loader to load a class and a resource bundle_ _respectively._ _Class.getMethodetc will use the immediate caller's class loader_ _to determine the security checks to be performed._ _-java.util.logging, Log4j and Groovy runtime filter the intermediary_ _stack frames (typically implementation-specific and reflection frames)_ _and find the caller's class to be used by the runtime of such library_ _or framework._ _- Traverse the entire stack trace or the stack trace of a Throwbale_ _and obtain additional information about classes for enhanced_ _diagnosibility in addition to the class and method name._ _This JEP will define a stack walk API that allows laziness, frame_ _filtering,_ _supports short reaches to stop at a frame matching some criteria_ _as well as long reaches to traverse the entire stack trace. This would_ _need the JVM to provide a flexible mechanism to traverse and materialize_ _the specific stack frame information to be used and allow efficient_ _lazy access to additional stack frames when required._ _Native JVM transitions should be minimzed._ _The API will define how it works when running with a security manager_ _that allows access to a Class` instance of any frame ensuring that the security is not compromised. An example API to walk the stack can be like: Thread.walkStack(Consumer action, int depthLimit) that takes a callback to be invoked for each frame traversed. A variant of the walkStack method will take a predicate for stack frame filtering. Thread.getCaller(Function<StackFrameInfo, R> function) Thread.findCaller(Predicate predicate, Function<StackFrameInfo, R> function) finds the caller frame with or without filtering. Testing ------- Unit tests and JCK tests for the new SE API will need to be developed. In addition, the performance of the new API for different use cases will be assessed.

Impact ------ - Performance/scalability: performance measurement shall be performed using micro-benchmarks as well as real world usage of getCallerClass replaced with the new API. - TCK: New JCK test cases shall be developed.

More information about the core-libs-dev mailing list