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Re: [cdt-dev] EDC and asynchronous operations

Hi John,


I agree, this is an important part of ACPM or any caching for that matter. There are different aspects to this:

1.       Keeping the cache consistent

a.       For the most part TCF services define events that control the consistency of the cache.  A client needs to act on these events to get proper results.

b.      There are services, e.g. Processes service, which do not have events.  In those cases the client needs to have a invalidation strategy, e.g. based on a timer, when the queue of pending requests empty, or other strategies.

2.       Limiting memory usage in the client

a.       It is not clear to me how important this is since clients only requires data that it is interested in and at least for debugging, the types of data that get has the potential to be very large is memory and that needs to be flushed when the context is suspended.  Of course in the general case, it is needed.

b.      In an environment, like Java, where there is a garbage collector I think it would be ideal if the cache implementation could be designed to allow the GC to collect cache elements when memory becomes low rather than having a separate mechanism that likely will not have a clear understanding of the correct memory pressure and therefore is likely to be too aggressive not aggressive enough. 

                                                               i.      This would probably require the use of weak references in the right places, so for example leaf nodes in the context hierarchy are collected before parents.





From: cdt-dev-bounces@xxxxxxxxxxx [mailto:cdt-dev-bounces@xxxxxxxxxxx] On Behalf Of John Cortell
Sent: Tuesday, October 26, 2010 9:30 AM
To: CDT General developers list.; CDT General developerslist.
Subject: Re: [cdt-dev] EDC and asynchronous operations


Felix and Eugene,

One thing I'm finding challenging about ACPM is managing the lifetime of cache objects. These things must live beyond the lifetime of the transaction that uses them since otherwise the transaction will perpetually fail. And when the transaction eventually completes successfully, it's beneficial to not discard the cache objects since there might be a transaction around the corner that needs the same data. At the same time, you don't want to keep piling up the cache objects indefinitely, for obvious memory footprint and performance reasons. So, I've been coding up a manager that tries to take these things into consideration. Did you guys have the same challenge with tcf-debug? Just wanted to check that there isn't some simplistic approach that's not becoming obvious to me.


At 04:23 PM 10/12/2010, Burton, Felix wrote:

Regarding 1: I don’t understand what you mean.  The following is simplified pseudo code that count number of frame on a stack by following a frame pointer list.
Boolean countStackFrames(Context ctx) {
                TCFDataCache<Register> fp = lookupRegisterCI(ctx, REGISTER_FP);
                if (!fp.validate(this)) {
                                return false;
                Address addr = fp.getData().valueAsAddress();
                long count = 0;
                while (addr != 0) {
                                TCFDataCache<Memory> mem = lookupMemoryCI(ctx, addr, address_size);
                                if (!mem.validate(this)) {
                                                return false;
                                addr = mem.getData().valueAsAddress();
                set(null, null, count);
                return true;
Regarding 2: I agree, we are not proposing that the asynchronous API should expose ACPM objects like cache instances.  Cache instances can be built on top of an asynchronous API to allow client to use ACPM instead of directly using the asynchronous API.  This is reflected on page 1 in the attached slides.  The TCF box on the bottom is exposing asynchronous APIs and on top of that are cache instances that expose ACPM APIs and on top of that is client code, e.g. code that assembles information that goes into a view, another cache instance, or other client.
Hope this helps,
From: cdt-dev-bounces@xxxxxxxxxxx [ mailto:cdt-dev-bounces@xxxxxxxxxxx] On Behalf Of John Cortell
Sent: Tuesday, October 12, 2010 1:41 PM
To: CDT General developers list.; CDT General developerslist.
Subject: Re: [cdt-dev] EDC and asynchronous operations
At 02:47 PM 10/12/2010, Burton, Felix wrote:

Felix, everything you wrote makes sense to me. Again, I definitely see the advantages of ACPM for the client of an async API that needs to make many API calls to carry out an operation. My points have been

1. ACPM is suitable only if you know the superset of all the data points your operation will need. There are many situations where this won't be the case.

2. ACPM seems to me a good tool for the client of an asynchronous API. However, It's not clear to me that an asynchronous API should expose ACPM objects, which I think is what Pawel was hinting at.


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