May 2006 - Boost-users - lists.preview.boost.org

Re: [Boost-users] Thread-safe smart pointers, hashtables without locking
by james.jones＠firstinvestors.com 04 May '06

04 May '06

From: Ray Whitmer <ray(a)personallegal.net> >which I then increment and decrement using the defined thread-safe >operators from the add_ref and release methods, which should give me >a relatively-thread-safe smart pointer with an internal count without >having to do any actual locking. [snip] >I am just posting here to see if anyone knows of a missed trick or >bad assumption I have made here using these or other boost mechaniisms. Personally, I read this and said, "eeek!" (Well, not literally. My office mates would wonder what was up.) I think any design like this is going to be (at best) very non-portable, and (more likely) subject to breaking at the worst possible moment (i.e. when demonstrating to a customer). Is "relatively" thread-safe really good enough here? As a constructive suggestion, if you want to reduce lock conflicts in hash tables, have you considered some form of finer-grained locking? You could, for example, have one lock per "slot" in your hash table. Computing the hash and finding the slot is thread-safe (since it doesn't depend on the state of the hash table), so you could then lock only the slot itself while performing list maintenance or whatever you need to do to read/write the data. This would be truly thread-safe but might perform better if you have lots of simultaneous readers/writers. I haven't tested this, but if you do, I'd be interested to hear the results. Regards, - James PS - I'd be even more worried in Java, btw, since Java opcodes should map to CPU operations less well than a compiled binary. Not to mention that in Java, the portability assumption becomes really critical. Java classes are *supposed* to be portable.

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Need help with integration of shared memory library (boost::shmem)
by Sascha Lumma 04 May '06

04 May '06

Shmem passed the review few month ago. Now I'd like to use it. But I found nothing about the integration into an existing boost distribution tree or to build the library stand alone. Firstly I tried to ununcompress the shmem*.zip (from Boost Sandbox Vault - Memory) into the boost distribution tree to build it all together. But there is no Jamfile in the shmem directories (only in the subdirectory 'test' and 'examples', but this is not the library). Which way I can take to get a working shmem library? many thanks, Sascha Lumma

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Re: [Boost-users] [date_time] So how come there isn't a to_time_t helper func?
by Scott 04 May '06

04 May '06

> I suspect that it's a plot by the date_time author to keep > people from using time_t ;-) > > Seriously though, while your function will work for some > times, there are issues: > > 1) ptime can represent dates prior to 1970-1-1 and after 2038 > (or wherever the upper bound of time_t is). Probably need an > exception for these cases on the conversion. > 2) ptime can represent times with less than 1 second > resolution. Maybe the function should round instead of > truncating in case the time is > 2006-May-04 00:00:00.999999? > > So if you're sure your application doesn't care about any of > these issues than the function above should be fine. > > Jeff Thanks for the super quick reply. That's the fastest response I've gotten from this list! :) My application is dealing with retrieving TCP/IP packets stored on disk, which are in time_t. But I use boost to convert a user readable date into packet time. In this particular case, the truncating is okay. I removed the date vetting code for clarity. Thanks, Scott

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[date_time] So how come there isn't a to_time_t helper func?
by Scott 04 May '06

04 May '06

I noticed there's a from_time_t() helper function, but I need to convert from a ptime to a time_t. Is this the proper way to do it? inline std::time_t to_time_t(ptime t) { ptime start(gregorian::date(1970,1,1)); time_duration dur = t - start; return dur.seconds(); } I'm also curious why such functionality isn't already available? Scott

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[boost][test] Location of up to date documentation?
by Ed Johnson 04 May '06

04 May '06

In a previous post, someone mentioned the BOOST_GLOBAL_FIXTURE to me. I used google desktop to search all the 1.33.1 doc's and release notes, but could not find any mention of it. I did a web search and found it on: http://lists.boost.org/Archives/boost/2005/12/98092.php [boost] [test] self-registration facilities Date: 2005-12-14 What is this newsgroup? It doesn't appear to be available for news readers on news.gmane.org. I don't see it mentioned or linked off of the main boost site either: http://www.boost.org/ Can someone guide me on the best way to find all the boost documentation for the latest releases? Many thanks, Ed

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boost.test - Can you determine order that Auto Test and Auto Suites will run among several test files?
by Ed Johnson 04 May '06

04 May '06

When using BOOST_AUTO_TEST_SUITE or BOOST_AUTO_TEST_CASE across multiple files, is there a way to guarantee which Test Case or Suite will execute last? In particular, I want the following test to always be executed last. BOOST_AUTO_TEST_CASE(waitForUserToPressEnter) { std::cout << "Press <ENTER> to continue..." << std::endl; std::cin.get(); } I like the post-build event trick to keeping output inside Visual Studio 7, but there will be times that I don't want the tests to all run each time I compile. Thanks, Ed

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Boost lambda: iter_swap and treating lambda as iterator.
by chun ping wang 04 May '06

04 May '06

K the question is simple. How do i do iterator swap with lambda. lets say i have vector of U. vector<U> vecU; typedef vector<U>::iterator iter; iter beg(vecU.begin()); for_each(vec.begin(), vec.end(), ( if_(_1 == *beg) [ // swap the iterator between the current one and begin. ] ) );

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[boost] [test] Need help with BOOST_GLOBAL_FIXTURE usage
by Ed Johnson 04 May '06

04 May '06

Hi, I tried to use the BOOST_GLOBAL_FIXTURE macro using 1.33.1, but I can't seem to get it to run. The breakpoints do not stop on it, and there is no output from the constructor or destructor. http://lists.boost.org/Archives/boost/2005/12/98092.php ------ #define BOOST_AUTO_TEST_MAIN #include <iostream> struct MyConfig { MyConfig() { std::cout << "global setup\n"; } ~MyConfig() { std::cout << "global teardown\n"; } }; BOOST_GLOBAL_FIXTURE( MyConfig ) ; BOOST_GLOBAL_FIXTURE( MyConfig m ) { m; } Any ideas? Thanks, Ed

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Fusion 2. Vector Example
by John Christopher 03 May '06

03 May '06

Hello, At the bottom of the page http://spirit.sourceforge.net/dl_more/fusion_v2/libs/fusion/doc/html/fusion… there is the following example: vector<int, float> v(12, 5.5f); std::cout << at<0>(v) << std::endl; std::cout << at<1>(v) << std::endl; The example as such does not compile, Shouldn't it be:std::cout << at_c<0>(v) << std::endl;orstd::cout << at<boost::mpl::int_<0> >(v) << std::endl;

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Thread-safe smart pointers, hashtables without locking
by Ray Whitmer 03 May '06

03 May '06

I found the boost libraries and templates as I was looking for thread- safe smart pointers. I was unable to use shared_ptr because I needed to be able to reconstitute a smart pointer from a raw pointer at any time without losing the count, so the count needs to be internal to the object, not external, so I am using intrusive_ptr. Since I need my intrusive_ptr to be thread-safe, I included: #include "boost/detail/atomic_count.hpp" and then I declared my internal count to be of type: boost::detail::atomic_count which I then increment and decrement using the defined thread-safe operators from the add_ref and release methods, which should give me a relatively-thread-safe smart pointer with an internal count without having to do any actual locking. This already seems like I may be going beyond the official interface by explicitly relying on something in the boost detail directory. Is it wrong to rely on this? But what I need now goes a bit further. I need a hashtable for which lookups are thread-safe without doing any locking. I only want to lock for adding or removing to/from the table. I already have the hashtable implementation that does this that I have used in Java for quite a while. In Java, I assumed the writing of a 32-bit reference into the hashtable array (or a null) was fairly atomic (which seemed reasonable on a 32-bit machine with normal alignment, etc). I made sure in the implementation that a writer who locks and changes the hashtable never temporarily places the hashtable into a state where it cannot be correctly read by any non- locking reader. I am hoping this will continue to work in C++ with the intrusive_ptr array of a hashtable. intrusive_ptr seems to contain a single 32-bit value which is likely to be atomic, at least as long as I avoid 16- bit architectures. Is there any better way to guarantee this? With the exception of the reference count, the objects being kept by the hashtable are read-only, so this should allow me any number of threads simultaneously operating on the same massive shared data hashtables (which can get cleaned up when no longer in use, by looking at ref counts). I am just posting here to see if anyone knows of a missed trick or bad assumption I have made here using these or other boost mechaniisms. Is the thread-safe hashtable that does not require locking for reading something that many others would benefit from? It is quite a simple implementation. Thanks, Ray Whitmer

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