Re: Classes on the stack trace (was: getElementClass/StackTraceElement, was: @CallerSensitive public API, was: sun.reflect.Reflection.getCallerClass)

[Jörn Huxhorn]

The numbers are from this link: http://stackoverflow.com/questions/421280/in-java-how-do-i-find-the-caller-of-a-method-using-stacktrace-or-reflection

Even if this benchmark suffers from micro-benchmark issues:
a slow-down of 10x would be bad, a slow-down of 100x would be a catastrophe.

I'd suggest to at least postpone the UnsupportedOperationException change until we find a suitable replacement. This change will also break existing Groovy scripts. See http://jira.codehaus.org/browse/GROOVY-6279 - but there are other issues as well.

Cheers,
Jörn.

On 29. Juli 2013 at 16:49:02, Nicholas Williams (nicholas+openjdk at nicholaswilliams.net) wrote:

I wasn't the one who ran the test, so I don't know for sure. My theory  
was that getCallerClass() returns a single frame, but the  
SecurityManager must allocate an array of appropriate size (which  
involves some overhead) and then return all of the frames. I chalked  
the difference up to that. My conclusion from the data was: If you  
need a whole stack, SecurityManager is clearly the best option. If you  
need a single frame, getCallerClass() is the only option that makes  
any sense.  

On Mon, Jul 29, 2013 at 8:21 AM, David M. Lloyd <david.lloyd at redhat.com> wrote:  
> I find it very interesting that reflection is no less than two orders of  
> magnitude faster than the security manager solution. How big was the stack  
> in these tests? It makes me wonder if maybe the implementation of the  
> security manager's getContext() method should be reevaluated a bit.  
>  
>  
> On 07/29/2013 07:53 AM, Nick Williams wrote:  
>>  
>> Just so that everyone understands how important this subject is, this  
>> change to getCallerClass(...) is being labeled a "disaster" for logging  
>> frameworks everywhere. Here's a benchmark for getting Classes from the  
>> following methods:  
>>  
>>> 1,000,000 calls of all alternatives were measured as follows :  
>>> Reflection: 10.195 ms.  
>>> Current Thread StackTrace: 5886.964 ms.  
>>> Throwable StackTrace: 4700.073 ms.  
>>> SecurityManager: 1046.804 ms.  
>>  
>>  
>> My goal here is to get the entire list engaged in coming up with the right  
>> solution. We (the community) can't afford for Java 8 not to have an  
>> equivalent replacement for getCallerClass().  
>>  
>> Nick  
>>  
>> On Jul 27, 2013, at 2:01 PM, Nick Williams wrote:  
>>  
>>> All,  
>>>  
>>> In the last two months, there have been a number of discussions  
>>> surrounding stack traces, Classes on the stack trace, and caller classes  
>>> [1], [2], [3]. These are all related discussions and the solution to them is  
>>> equally related, so I wanted to consolidate it all into this one discussion  
>>> where I hope we can finalize on a solution and get it implemented for Java  
>>> 8.  
>>>  
>>> In a nut shell, here are the underlying needs that I have seen expressed  
>>> through many, many messages:  
>>>  
>>> - Some code needs to get the Class of the caller of the current method,  
>>> skipping any reflection methods.  
>>> - Some code needs to get the Class of the caller /n/ stack frames before  
>>> the current method, skipping any reflection methods.  
>>> - Some code needs to get the current stack trace, populated with Classes,  
>>> Executables, file names, line numbers, and native flags instead of the  
>>> String class names and String method names in StackTraceElement. This  
>>> /should/ include any reflection methods, just like StackTraceElement[]s.  
>>> - Some code needs to get the stack trace from when a Throwable was  
>>> created, populated with Classes, Executables, file names, line numbers, and  
>>> native flags instead of the String class names and String method names in  
>>> StackTraceElement. This /should/ include any reflection methods, just like  
>>> StackTraceElement[]s.  
>>> - There needs to be a reflection way to achieve all of this since some  
>>> libraries (e.g., Log4j) need to be compiled against Java 6 but run on 7 and  
>>> 8 (and thus can't use @CallerSensitive).  
>>>  
>>> I believe the solutions to these needs are all related. Importantly, I  
>>> think it is very important that action be taken in Java 8 due to the changes  
>>> made to sun.reflect.Reflection#getCallerClass(...). While we all understand  
>>> that relying on private sun.* APIs is not safe, the fact is that many people  
>>> have relied on sun.reflect.Reflection#getCallerClass(...) due to the fact  
>>> that there is simply no other way to do this in the standard API. This  
>>> includes Log4j 2, Logback, SLF4j, and Groovy, some features of which will  
>>> stop working correctly in Java 7 >= u25.  
>>>  
>>> I would point out that this could all easily be solved simply by adding a  
>>> getElementClass() method to StackTraceElement, but there was strong  
>>> opposition to this, largely due to serialization issues. Since that is  
>>> apparently not an option, I propose the following API, based on the various  
>>> discussions in the last two months, StackTraceElement, and the API that .NET  
>>> provides to achieve the same needs as listed above:  
>>>  
>>> CallerSensitive.java:  
>>> package java.lang;  
>>>  
>>> /** Previously private API, now public */  
>>> public @interface CallerSensitive {  
>>> ...  
>>> }  
>>>  
>>> StackTraceFrame.java:  
>>> package java.lang;  
>>>  
>>> import java.util.Objects.  
>>>  
>>> public final class StackTraceFrame {  
>>> private final Class<?> declaringClass;  
>>> private final Executable executable;  
>>> private final String fileName;  
>>> private final int lineNumber;  
>>>  
>>> public StackTraceFrame(Class<?> declaringClass, Executable  
>>> executable, String fileName, int lineNumber) {  
>>> this.declaringClass = Objects.requireNonNull(declaringClass,  
>>> "Declaring class is null");  
>>> this.executable = Objects.requireNonNull(executable, "Executable  
>>> is null");  
>>> this.fileName = fileName;  
>>> this.lineNumber = lineNumber;  
>>> }  
>>>  
>>> public Class<?> getDeclaringClass() {  
>>> return this.declaringClass;  
>>> }  
>>>  
>>> public Executable getExecutable() {  
>>> return this.executable;  
>>> }  
>>>  
>>> public String getFileName() {  
>>> return this.fileName;  
>>> }  
>>>  
>>> public int getLineNumber() {  
>>> return this.lineNumber;  
>>> }  
>>>  
>>> public boolean isNative() {  
>>> return this.lineNumber == -2;  
>>> }  
>>>  
>>> public String toString() { /* Same as StackTraceElement */ }  
>>> public boolean equals() { /* Ditto */ }  
>>> public int hashCode() { /* Ditto */ }  
>>>  
>>> /** Uses @CallerSensitive */  
>>> public static native StackTraceFrame getCallerFrame();  
>>>  
>>> /** Works like Java < 7u25 sun.reflect.Reflection#getCallerClass()  
>>> */  
>>> public static native StackTraceFrame getCallerFrame(int skipFrames);  
>>>  
>>> public static native StackTraceFrame[] getCurrentStackTrace();  
>>> }  
>>>  
>>> Throwable.java:  
>>> package java.lang;  
>>>  
>>> ...  
>>>  
>>> public class Throwable {  
>>> ...  
>>> public synchronized Throwable fillInStackTraceFrames() { ... }  
>>>  
>>> private native Throwable fillInStackTraceFrames(int dummy);  
>>>  
>>> public StackTraceFrame[] getStackTraceFrames() {  
>>> return this.getOurStackTraceFrames().clone();  
>>> }  
>>>  
>>> private synchronized StackTraceFrame[] getOurStackTraceFrames() {  
>>> ... }  
>>> ...  
>>> }  
>>>  
>>> Furthermore, I propose that we restore the behavior of  
>>> sun.reflect.Reflection#getCallerClass(int) /just for Java 7/ since the  
>>> proposed above solution cannot be added to Java 7.  
>>>  
>>> I would love if we could quickly coalesce around this solution or a  
>>> derivative thereof so that it can be implemented before Feature Complete.  
>>> The absence of any replacement or alternative for  
>>> sun.reflect.Reflection#getCallerClass(int) will be a serious issue in Java 8  
>>> that will cause hardships for many projects.  
>>>  
>>> [1]  
>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-June/018049.html  
>>> [2]  
>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-June/018349.html,  
>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-July/019098.html  
>>> [3]  
>>> http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-July/018855.html  
>>  
>>  
>  
>  
> --  
> - DML