关于并行I / O的一些测试中发生了一个非常奇怪的情况。这是一种情况。我有多个线程将文件处理程序打开到同一文件，并从文件的多个位置（均匀间隔）读取有限数量的字节并将其转储到数组中。所有这些都是通过增强线程完成的。现在，我假设由于随机访问的原因，HDD应该更慢。这就是为什么我的测试实际上针对SSD的原因。事实证明，与HDD相比，从固态磁盘读取同一文件时，几乎没有任何加速。想知道问题可能是什么？这对我来说是否真的很令人惊讶/我也在下面发布了我的代码以查看我的实际工作：
void readFunctor(std::string pathToFile, size_t filePos, BYTE* buffer, size_t buffPos, size_t dataLn, boost::barrier& barier) {
FILE* pFile;
pFile = fopen(pathToFile.c_str(), "rb");
fseek(pFile, filePos, SEEK_SET);
fread(buffer, sizeof(BYTE), dataLn, pFile);
fclose(pFile);
barier.wait();
}
void joinAllThreads(std::vector<boost::shared_ptr<boost::thread> > &threads) {
for (std::vector<boost::shared_ptr<boost::thread> >::iterator it = threads.begin(); it != threads.end(); ++it) {
(*it).get()->join();
}
}
void readDataInParallel(BYTE* buffer, std::string pathToFile, size_t lenOfData, size_t numThreads) {
std::vector<boost::shared_ptr<boost::thread> > threads;
boost::barrier barier(numThreads);
size_t dataPerThread = lenOfData / numThreads;
for (int var = 0; var < …如何理解下面这段代码？我是Rust的新手,但有C/Haskell背景和一点点C++.我能找到的唯一参考是减轻强制.
fn main() {
let xs: [u32; 4] = [0, 1, 2, 3];
let mut i: u32 = 0;
for x in xs.iter() {
if i > *x { // It looks x is an iterator. Understood.
i = i + x; // no error. (coerced)
//Quote: "Rust will do this as many times
// as possible until the types match."
i = i + *x; // no error (explicit deref)
i += x; // error about u32/&u32 …它来自另一个问题,但情况发生了变化.
Parsec函数'parse'的类型签名和类'Stream'
我现在想知道如何import做出与众不同的事情.
文件:RunParse.hs
module RunParse where
import System.IO
import Data.Functor.Identity (Identity)
----import Text.Parsec () ....................(1)
----import Text.Parsec ....................(2)
import Text.Parsec.Prim (Parsec, parse, Stream)
runIOParse :: (Show a) => Parsec String () a -> String -> IO ()
runIOParse pa fn =
do
inh <- openFile fn ReadMode
outh <- openFile (fn ++ ".parseout") WriteMode
instr <- hGetContents inh
let result = case parse pa fn instr of
Right rs -> show rs
Left err -> "error"
hPutStr …我总是const用来保护不应该分配的值.无论如何,在某些情况下,我可能需要初始化变量,然后const在同一函数中将其用作值.例如:
void foo() {
int flags;
/* ... */
if (condition1)
flags |= 1;
/* .... */
if (conditionX)
flags |= Y;
/* .... */
// start using flags as a const value
const flags; // <<= I want something like this.
const int c_flags = flags; // <<= What I have to do. The naming is annoying.
/* ... */
}
有没有办法改善这个？可以是编码样式或高级语言功能.
从@Potatoswatter:对于gcc/clang中的C(gnu样式,比方说,-std = gnu11),可以使用Statement Expression.
foo() {
const int flags = ({
int f …