This allows one to use SGPath in containers such as std::map,
std::unordered_map and std::unordered_set.
Like the existing == and !=, all these operators rely solely on the
UTF-8 internal representation of the path.
We'll use this to cleanly declare std::hash<SGPath> as 'noexcept' in the
next commit, which appears to be desirable for std::hash template
specializations, according to:
http://en.cppreference.com/w/cpp/utility/hash
This is done by simply not user-defining the copy constructor,
copy-assignment operator and destructor. See [1] for more info.
[1] http://accu.org/content/conf2014/Howard_Hinnant_Accu_2014.pdf
For the benchmark below (compiled with the next commit to allow sorting
SGPath instances), on Linux amd64 with g++ 6.3.0, I observe that
enabling SGPath move operations with this commit increases the
performance by 31% or 28% respectively, depending on whether I use this:
// Typical code that creates a data structure in several steps and
// benefits from move operations (the std::move() does nothing when
// running the test with move operations disabled: a copy is made).
auto p = SGPath::fromUtf8(randomString(0, 30));
v.emplace_back(std::move(p));
or that:
v.emplace_back(randomString(0, 30))
for the initialization code. Now the benchmark code:
using std::string;
static std::default_random_engine randomNumbersGenerator;
// Utility function: generate a random string whose length is in the
// [minLen, maxLen] range.
string randomString(string::size_type minLen, string::size_type maxLen)
{
std::uniform_int_distribution<string::size_type> sLenDist(minLen, maxLen);
std::uniform_int_distribution<int> byteDist(0, 255);
auto randomByte = std::bind(byteDist, randomNumbersGenerator);
string::size_type len = sLenDist(randomNumbersGenerator);
string str;
while (str.size() < len) {
str += std::char_traits<char>::to_char_type(randomByte());
}
return str;
}
// The test function, run with nbIterations = 500000, minSize = 0 and
// maxSize = 200 to obtain the figures given above.
void SGPath_perfTest(std::size_t nbIterations,
std::size_t minSize, std::size_t maxSize)
{
std::uniform_int_distribution<std::size_t> sizeDist(minSize, maxSize);
auto randomSize = std::bind(sizeDist, randomNumbersGenerator);
std::chrono::time_point<std::chrono::system_clock> start, end;
start = std::chrono::system_clock::now();
vector<SGPath> v;
for (std::size_t i=0; i < nbIterations; i++) {
v = vector<SGPath>{}; // start anew
for (std::size_t j=0; j < randomSize(); j++) {
v.emplace_back(randomString(0, 30));
}
std::shuffle(v.begin(), v.end(), randomNumbersGenerator);
std::sort(v.begin(), v.end());
}
end = std::chrono::system_clock::now();
std::chrono::duration<double> elapsedSecs = end - start;
std::cout << elapsedSecs.count() << "\n"; // duration in seconds
}
With this simple change, the speedup as compared to commit 18f048424 is
now 37 % for the benchmark given in the previous commit. This is because
optimized swap() only needs to swap the raw pointers, which is certainly
less work than the three move assignments on SGSharedPtr (not raw
pointers) done by std::swap().
To benefit from this, write code like:
using std::swap; // now useless for SGSharedPtr, but idiomatic
swap(ptr1, ptr2); // *not* std::swap()!
This automatically makes SGSharedPtr more efficient when used in
standard containers (among others). See below for the benchmark details.
Mark as 'noexcept' (after checking it's legitimate!) the SGSharedPtr and
SGReferenced methods required for SGSharedPtr's move constructor and
move assignment operator to be guaranteed 'noexcept'.
Benchmark
---------
I measured a 25 % speedup with g++ 6.3.0 on Linux amd64, CFLAGS=-Wall -O2
as compared to commit 18f0484249 (which is
just before my changes to SGSharedPtr.hxx) on the following test code,
called with:
nbIterations = 3000000
minSize = 0
maxSize = 200
------------------------------------------------------------------------
static std::default_random_engine randomNumbersGenerator;
class SGReferencedTestClass : public SGReferenced
{ int i; };
void SGSharedPtr_perfTest(std::size_t nbIterations,
std::size_t minSize, std::size_t maxSize)
{
using Ref = SGSharedPtr<SGReferencedTestClass>;
std::uniform_int_distribution<std::size_t> sizeDist(minSize, maxSize);
auto randomSize = std::bind(sizeDist, randomNumbersGenerator);
std::chrono::time_point<std::chrono::system_clock> start, end;
start = std::chrono::system_clock::now();
std::vector<Ref> v;
for (std::size_t i=0; i < nbIterations; i++) {
v = std::vector<Ref>{}; // start anew
for (std::size_t j=0; j < randomSize(); j++) {
auto p = Ref(new SGReferencedTestClass());
v.emplace_back(std::move(p));
}
std::shuffle(v.begin(), v.end(), randomNumbersGenerator);
std::sort(v.begin(), v.end());
}
end = std::chrono::system_clock::now();
std::chrono::duration<double> elapsedSecs = end - start;
std::cout << elapsedSecs.count() << "\n"; // duration in seconds
}
------------------------------------------------------------------------
Basically, these gains can be explained by the fact that copying an
SGSharedPtr requires to test SGReferenced::ref, increase the refcount,
and then when the object is destroyed, test again SGReferenced::ref,
decrease the refcount and test it in order to maybe delete. With the
move constructor and move assignment operator, copying the argument is
never necessary: its raw pointer can be swapped with the one contained
in *this, which is very fast. For the move constructor, this is all that
is needed; move assignment just needs one reset() call after that in
order to release the resource from the moved-from shared pointer.
The copy-and-swap idiom is certainly very cute, but often causes
unnecessary copies. My commit fedafb9352
did exactly that, unfortunately.
Restore the exact same code for the copy-assignment operator as before
commit fedafb935, and add a more efficient implementation for the
move-assignment operator.
As explained by Howard Hinnant in [1] and [2], if some particular piece
of code really needs a strong exception safety guarantee, one can easily
add a specific method for that; this is not a valid reason to make the
code slower for all other places that have no use for such a guarantee!
[1] http://www.slideshare.net/ripplelabs/howard-hinnant-accu2014
[2] https://stackoverflow.com/a/9322542/4756009
In C++11, destructors are 'noexcept' by default -> remove useless
throw() specifiers. There was one case that wasn't about a destructor: I
replaced the 'throw()' with 'noexcept' because this use of 'throw()' is
deprecated and 'noexcept' offers the intended meaning as far as I can
guess (in C++17, 'throw()' will be equivalent to 'noexcept' anyway). For
more info, see:
http://en.cppreference.com/w/cpp/language/noexcept_spechttps://akrzemi1.wordpress.com/2013/08/20/noexcept-destructors/
Avoids codecvt dependency on Unix where it might not be present, eg
with GCC 4.8; on Windows we use <codecvt> since it’s present in VS2015
to avoid writing a seperate UTF-16 <-> UTF-8 conversion.
Designed for 2d objects, such as a canvas placements, this permits the receipt of touch (mouse click) events to enable the simulation of avionics with a touchscreen.
The coordinates are passed in as arguments to the action; these can be accessed with Nasal via the cmdarg() method.
example:
<animation>
<type>touch</type>
<visible>true</visible>
<object-name>VSDImage</object-name>
<action>
<touch>0</touch>
<repeatable>false</repeatable>
<binding>
<command>nasal</command>
<script>print("touch input
(",cmdarg().getNode("x").getValue(),",",cmdarg().getNode("y").getValue())</script>
</binding>
</action>
</animation>
simgear::Dir::isEmpty() used to make up to 5 calls to readdir(), while 3
are enough to say whether the directory has entries other than '.' and
'..'.
Also add an automated test for this method.
This is done so as to avoid confusion with the unrelated classes
ResourceProvider and ResourceManager already present in SimGear.
Despite this new name, EmbeddedResourceProxy is a proxy not only for
embedded resources, but also for real files (hence the initial name
choice): its purpose is precisely to allow zero-work switching from one
data source to the other.
The ResourceProxy class allows one to access real files or embedded
resources in a unified way. When using it, one can switch from one data
source to the other with minimal code changes, possibly even at runtime
(in which case there is obviously no code change at all).
Sample usage (from FlightGear for the globals->get_fg_root() bit):
simgear::ResourceProxy proxy(globals->get_fg_root(), "/FGData");
std::string s = proxy.getString("/some/path");
std::unique_ptr<std::istream> streamp = proxy.getIStream("/some/path");
The methods ResourceProxy::getString(const std::string& path) and
ResourceProxy::getIStream(const std::string& path) decide whether to use
embedded resources or real files depending on the boolean value passed
to ResourceProxy::setUseEmbeddedResources() (also available as an
optional parameter to the ResourceProxy constructor, defaulting to
true). It is often most convenient to set this boolean once and don't
worry about it anymore---it's stored inside the ResourceProxy object.
Otherwise, if you want to fetch resources some times from real files,
other times from embedded resources, you may use the following methods:
// Retrieve contents using embedded resources
std:string s = proxy.getString("/some/path", true);
std:string s = proxy.getStringDecideOnPrefix(":/some/path");
// Retrieve contents using real files
std:string s = proxy.getString("/some/path", false);
std:string s = proxy.getStringDecideOnPrefix("/some/path");
(alternatively, you could use several ResourceProxy objects with
different values for the constructor's third parameter)
