我需要使用C ++来测量上下文切换的时间。我知道我可以简单地从C ++代码访问C函数，但任务是尽可能避免使用C语言。我在互联网上搜索了这个，但发现只有这样做的方法使用C.有没有办法在C ++中使用OS？来自pipe(...)的{{1}}，来自unistd.h的{{1}}和其他人的sched_setaffinity(...)类似物？
答案 0 :(得分：1)
更新2017-06-30：添加了示例代码
Are there any ways to work with OS in C++?
您引用的所有C函数都可以通过直接包含访问。 例如：
#include "pthread.h"
在C ++编译中，自动神奇地获得extern“C”d。
您的链接在Linux上需要-lrt和-pthread
Any analogs of pipe(...) from unistd.h, sched_setaffinity(...)
不是类比，构建链接到真正的“C”Linux函数。
I need to measure the time of context switching using C++ means.
我通过重复一些动作1到10秒来计算持续时间，并计算循环完成的次数。
在我最新的次要基准测试中，完全用C ++编写（但不使用C ++ 11功能），我
将N个线程的信号量分发给节点线程并关闭循环 在列表的末尾（即end-list-node输出信号量句柄指向 begin-list-node输入信号量句柄）
主要任务，用semGive（）开始连锁反应，等待10秒钟（使用 usleep），然后设置每个线程都可以看到的标志。
示例在6岁的戴尔上运行。
Compilation started at Wed Jan 15 22:31:33
./lmbm101
lmbm101: context-switch duration .. wait up to 10 seconds while measuring.
switch enforced using pthread_mutex semaphores
C5 bogomips: 5210.77 5210.77
686.56 kilo m_thread_switch invocations in 10.88 sec (10000088 us)
68.6554 kilo m_thread_switch events per second
14.5655 u seconds per m_thread_switch event
pid = 12188
now (52d760af): 22:31:43
bdtod 2014/01/15 22:31:43 minod=1351 iod=91 secod=81103 soi=104
我在C ++ 11发布之前做了这个小基准测试。这段代码是用C ++ 11编译的，但不使用C ++ 11任务......对我来说是未来的努力。
更新2017-06-30 - 逾期更新...
我写了这个示例代码2017-04。我现在倾向于使用std :: vector来处理各种事情。以前的测量没有。类似的技术，但简化的结果报告。
#include <chrono>
#include <iomanip>
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <thread>
#include <vector>
// see EngFormat-Cpp-master.zip
#ifndef ENG_FORMAT_H_INCLUDED
#include "../../bag/src/eng_format.hpp" // to_engineering_string(), from_engineering_string()
#endif
#include <cassert>
#include <semaphore.h> // Note 1 - Ubuntu / Posix feature access, see PPLSEM_t
namespace DTB // doug's test box
{
// Note 2 - typedefs to simplify chrono access
// 'compressed' chrono access --------------vvvvvvv
typedef std::chrono::high_resolution_clock HRClk_t; // std-chrono-hi-res-clk
typedef HRClk_t::time_point Time_t; // std-chrono-hi-res-clk-time-point
typedef std::chrono::microseconds NS_t; // std-chrono-nanoseconds
typedef std::chrono::microseconds US_t; // std-chrono-microseconds
typedef std::chrono::microseconds MS_t; // std-chrono-milliseconds
using namespace std::chrono_literals; // support suffixes like 100ms, 2s, 30us
// examples:
// Time_t testStart_us = HRClk_t::now();
// auto testDuration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - testStart_us);
// auto count_us = testDuration_us.count();
// or
// std::cout << " complete " << testDuration_us.count() << " us" << std::endl;
// C++ access to Linux semaphore via Posix
// Posix Process Semaphore, set to Local mode (unnamed, unshared)
class PPLSem_t
{
public: // shared-between-threads--v v--initial-value is unlocked
PPLSem_t() { assert(0 == ::sem_init(&m_sem, 0, 1)); } // ctor
~PPLSem_t() { assert(0 == ::sem_destroy(&m_sem)); } // dtor
int lock() { return (::sem_wait(&m_sem)); } // returns 0 when success, else -1
int unlock() { return (::sem_post(&m_sem)); } // returns 0 when success, else -1
void wait() { assert(0 == lock()); }
void post() { assert(0 == unlock()); }
private:
::sem_t m_sem;
};
// POSIX is an api, this C++ class simplifies use
// sem_wait and sem_post are possibly assembly for best performance
// Note 3 - locale what now?
// insert commas from right to left -- change 1234567890 to 1,234,567,890
// input 's' is the digits-to-the-left-of-the-decimal-point
// returns s contents with inserted comma's
std::string digiComma(std::string s)
{ //vvvvv--sSize must be signed int of sufficient size
int32_t sSize = static_cast<int32_t>(s.size());
if (sSize > 3)
for (int32_t indx = (sSize - 3); indx > 0; indx -= 3)
s.insert(static_cast<size_t>(indx), 1, ',');
return(s);
}
const std::string dashLine(" --------------------------------------------------------------\n");
// Note 5 - thread sync to wall clock
// action: pauses a thread, resume thread action at next wall-clock-start-of-second
void sleepToWallClockStartOfSec(std::time_t t0 = 0)
{
if (0 == t0) { t0 = std::time(nullptr); }
while(t0 == std::time(nullptr)) {
std::this_thread::sleep_for(100ms); } // good-neighbor-thread
}
// a good-neighbor-thread delay does not 'hog' a processor
// Note 4 - typedef examples to simplify
// create new types based on vector ... suffix '_t' reminds that this is a type
typedef std::vector<uint> UintVec_t;
typedef std::vector<uint> TIDSeqVec_t;
typedef std::vector<std::thread*> Thread_pVec_t;
// measure -std=C++14 std::thread average context switch duration
// enforced with one PPLSem_t
class Q6_t
{
// private data
const uint MaxThreads; // thread count
const uint MaxSecs; // seconds of test
const std::string m_TIDSeqPFN; // capture tid seq to ram (write to file later)
//
uint m_thrdSwtchCount; // count incremented by all threads
//
bool m_done; // main to threads: cease and desist
uint m_rdy; // threads to main: thread is ready! (running)
PPLSem_t m_sem; // one semaphore shared by all threads
//
UintVec_t m_thrdRunCountVec; // counts incremented per thread
TIDSeqVec_t m_TIDSeq_Vec; // sequence (order) of thread execution
Thread_pVec_t m_thread_pVec; // vector of thread pointers
public:
Q6_t() // default ctor
: MaxThreads(10) // total threads
, MaxSecs(10) // controlled seconds of test
, m_TIDSeqPFN("./Q6.txt") // where put data file
//
, m_thrdSwtchCount(0)
//
, m_done(false) // main() to threads: cease and desist
, m_rdy(0) // threads to main(): thread is ready!
// m_sem // default ctor ok
//
// m_thrdRunCountVec // default ctor ok
// m_TIDSeq_Vec // default ctor ok
// m_thread_pVec // default ctor ok
{
for (size_t i = 0; i < MaxThreads; ++i) {
m_thrdRunCountVec.push_back(0); // 0 each per-thread counter
}
// your results -----vvvvvvvv----will vary
m_TIDSeq_Vec.reserve(45000000); // observed as many as 42,000,000 on my old Dell
m_thread_pVec.reserve(MaxThreads);
// DO NOT start threads (m_thread_pVec) yet
} // AciveObj_t()
~Q6_t()
{
// m_TIDSeq_Vec,
while(m_thread_pVec.size()) { // more to pop and delete
std::thread* t = m_thread_pVec.back(); // return last element
m_thread_pVec.pop_back(); // remove last element
delete t; // delete thread
}
// m_thrdRunCountVec;
// m_TIDSeqPFN, m_sem, m_rdy; m_done;
// m_thrdSwtchCount; MaxSecs; MaxThreads;
} // ~Q6_t()
// Q6_t::main(..) runs in context thread 'main()', invoked in function main()
int main(std::string label)
{
std::cout << dashLine << " " << MaxSecs << " second measure of "
<< MaxThreads << " threads, 1 PPLSem_t " << label << "\n"
<< " output: " << m_TIDSeqPFN << '\n'<< std::endl;
assert(0 == m_sem.lock()); // take posession of m_sem
// now all thread will block at critical section entry (in onceThruCritSect())
std::cout << "\n block threads at crit sect " << std::endl;
createAndActivateThreads();
long int durationUS = 0;
releaseThreadsAndWait(durationUS); // run threads run
std::cout << "\n" << std::endl
<< report(" 'thread context switch' ",
m_thrdSwtchCount, durationUS);
reportThreadActionCounts();
writeTIDSeqToQ6_txt();
reportMainStackSize();
measure_LockUnlock(); // with no context switch, no collision
return(0);
} // int main() // in 'main' context
private:
void onceThru(uint id) // a crit section
{
assert(0 == m_sem.lock()); // critical section entry
{
m_thrdSwtchCount += 1; // 'work'
m_thrdRunCountVec[id] += 1; // diagnostic - thread work-balance
m_TIDSeq_Vec.push_back(id); // thread sequence capture
}
assert(0 == m_sem.unlock()); // critical section exit
}
// thread entry point
void threadRun(uint id)
{
std::cout << '.' << id << std::flush; // ".0.1.2.3.4.5.6.7.8.9"
m_rdy |= (1 << id); // thread to main: i am ready
do {
onceThru(id);
if (m_done) break; // exit when done tbr - FIXME -- rare hang
}while(true);
}
// main() context: create and activate std::thread's with new
void createAndActivateThreads() // main() context
{
std::cout << " createAndActivateThreads() ";
Time_t start_us = HRClk_t::now();
for (uint id = 0; id < MaxThreads; ++id)
{
// std::thread activates when instance created
std::thread* thrd = new
std::thread(&Q6_t::threadRun, this, id);
// method-------^^^^^^^^^^^^^^^ ^^--single param for method
// instance*---------------------^^^^
assert(nullptr != thrd);
// create handshake mask for unique 'id' bit of m_rdy
uint mask = (1 << id);
// wait for bit set in m_rdy by thread
while ( ! (mask & m_rdy) ) {
std::this_thread::sleep_for(100ms); // not a poll
}
// thread has confirmed to main() that it is running
// capture pointer to invoke join's
m_thread_pVec.push_back(thrd);
}
auto duration_us =
std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);
std::cout << " (" << digiComma(std::to_string(duration_us.count()))
<< " us)" << std::endl;
sleepToWallClockStartOfSec(); // start-of-second
} // void createAndActivateThreads()
// main() context: measure average context switch duration
// by releasing threads to run
void releaseThreadsAndWait(long int& count_us)
{
Time_t testStart_us = HRClk_t::now();
// thread 'main()' is current owner of this semaphore - see "Q6_t::main()"
assert(0 == m_sem.unlock()); // release the hounds
std::cout << " releaseThreadsAndWait " << std::flush;
// progress indicator to user
for (size_t i = 0; i < MaxSecs; ++i) // let threads switch for 10 seconds
{
sleepToWallClockStartOfSec(); // 'main()' sync's to wall clock
std::cout << (MaxSecs-i-1) << ' ' << std::flush; // "9 8 7 6 5 4 3 2 1 0"
}
// tbr - dedicated mutex for this single-write / multiple read ? or std::atomic ?
m_done = true; // command threads to exit - all threads can see m_done
auto testDuration_us =
std::chrono::duration_cast<US_t>(HRClk_t::now() - testStart_us);
count_us = testDuration_us.count();
// tbr - main() shall confirm all threads complete
// tbr - measure how long to detect m_done
Time_t joinStart_us = HRClk_t::now();
std::cout << "\n join threads ";
for (size_t i = 0; i < MaxThreads; ++i)
{
m_thread_pVec[i]->join(); // main() waits here for thread[i] completion
std::cout << ". " << std::flush;
}
auto joinDuration_us =
std::chrono::duration_cast<US_t>(HRClk_t::now() - joinStart_us);
std::cout << " (" << digiComma(std::to_string(joinDuration_us.count()))
<< " us)" << std::endl;
} // void releaseThreadsAndWait(long int& count_us)
void reportThreadActionCounts()
{
std::cout << "\n each thread run count: \n ";
uint sum = 0;
for (auto it : m_thrdRunCountVec)
{
std::cout << std::setw(11) << digiComma(std::to_string(it));
sum += it;
}
std::cout << std::endl;
uint diff = (sum - m_thrdSwtchCount);
std::cout << ' ';
double maxPC = 0.0;
double minPC = 100.0;
for (auto it : m_thrdRunCountVec)
{
double percent = static_cast<double>(it) / static_cast<double>(sum);
if(percent > maxPC) maxPC = percent;
if(percent < minPC) minPC = percent;
std::cout << std::setw(11) << (percent * 100);
}
std::cout << " (% of total)\n\n total : " << digiComma(std::to_string(sum));
if (diff) std::cout << " (diff: " << diff << ")";
std::cout << " note variability -- min : " << (minPC*100)
<< "% max : " << (maxPC*100) << "%" << std::endl;
} // void reportThreadActionCounts()
void writeTIDSeqToQ6_txt() // m_TIDSeq_Vec - record sequence of thread access to critsect
{
size_t sz = m_TIDSeq_Vec.size();
std::cout << '\n' << dashLine << " writing Thread ID sequence of "
<< digiComma(std::to_string(sz)) << " values to "
<< m_TIDSeqPFN << std::endl;
Time_t writeStart_us = HRClk_t::now();
do {
std::ofstream Q6cout(m_TIDSeqPFN);
if ( ! Q6cout.good() )
{
std::cerr << "not able to open for write: " << m_TIDSeqPFN << std::endl;
break;
}
size_t lnSz = 0;
for (auto it : m_TIDSeq_Vec)
{
// encode Thread ID uints: 0 1 2 3 4 5 6 7 8 9
// to letters 'A' thru 'J': vvvvvv 'A' 'B' 'C' 'D' 'E' 'F' 'G' 'H' 'I' 'J'
Q6cout << static_cast<char>(it+'A');
// whitespace not needed
if (++lnSz > 100) { Q6cout << std::endl; lnSz = 0; } // 100 chars per line
}
Q6cout << '\n' << std::endl;
Q6cout.close();
} while(0);
auto wDuration_us = std::chrono::duration_cast<US_t>
( HRClk_t::now() - writeStart_us );
std::cout << " complete: "
<< digiComma(std::to_string(wDuration_us.count()))
<< " us" << std::endl;
} // writeTIDSeqToQ6_txt
std::string report(std::string lbl, uint64_t eventCount, uint64_t duration_us)
{
std::stringstream ss;
ss << " " << to_engineering_string(static_cast<double>(eventCount),9,eng_prefixed)
<< lbl << " events in " << digiComma(std::to_string(duration_us)) << " us" << std::endl;
double eventsPerSec = (1000000.0*(static_cast<double>(eventCount))/
static_cast<double>(duration_us));
ss << " " << to_engineering_string(eventsPerSec,9,eng_prefixed)
<< lbl << " events per second\n "
<< to_engineering_string((1.0/eventsPerSec), 9, eng_prefixed)
<< " sec per " << lbl << " event " << std::endl;
return(ss.str());
} // std::string report(std::string lbl, uint64_t eventCount, uint64_t duration_us)
// Note 6 - stack size -> use POSIX 'pthread_attr_...' API
void reportMainStackSize()
{
pthread_attr_t tattr;
int stat = pthread_attr_init (&tattr);
assert(0 == stat);
size_t size;
stat = pthread_attr_getstacksize(&tattr, &size);
assert(0 == stat);
std::cout << '\n' << dashLine << " Stack Size: "
<< digiComma(std::to_string(size))
<< " [of 'main()' by pthread_attr_getstacksize]\n"
<< std::endl;
stat = pthread_attr_destroy(&tattr);
assert(0 == stat);
} // void reportMainStackSize()
// Note 7 - semaphore API performance
// measure duration when no context switch (i.e. no thread 'collision')
void measure_LockUnlock()
{
//PPLSem_t* sem1 = new PPLSem_t;
//assert(nullptr != sem1);
PPLSem_t sem1;
size_t count1 = 0;
size_t count2 = 0;
std::cout << dashLine << " 3 second measure of lock()/unlock()"
<< " (no collision) " << std::endl;
time_t t0 = time(0) + 3;
Time_t start_us = HRClk_t::now();
do {
assert(0 == sem1.lock()); count1 += 1;
assert(0 == sem1.unlock()); count2 += 1;
if(time(0) > t0) break;
}while(1);
auto duration_us = std::chrono::duration_cast<US_t>(HRClk_t::now() - start_us);
assert(count1 == count2);
std::cout << report (" 'sem lock()+unlock()' ", count1, duration_us.count());
std::cout << "\n";
} // void mainMeasures_LockUnlock()
}; // class Q6_t
} // namespace DTB
int main(int argc, char* argv[] )
{
std::cout << "\nargc: " << argc << '\n' << std::endl;
for (int i=0; i<argc; i+=1) std::cout << argv[i] << " ";
std::cout << "\n" << std::endl;
setlocale(LC_ALL, "");
std::ios::sync_with_stdio(false);
{
std::time_t t0 = std::time(nullptr);
std::cout << " " << std::asctime(std::localtime(&t0)) << std::endl;;
DTB::sleepToWallClockStartOfSec(t0);
}
DTB::Time_t main_start_us = DTB::HRClk_t::now();
int retVal = 0;
{
DTB::Q6_t q6;
retVal = q6.main(" Q6::main() ");
}
auto duration_us = std::chrono::duration_cast<DTB::US_t>
(DTB::HRClk_t::now() - main_start_us);
std::cout << " FINI "
<< DTB::digiComma(std::to_string(duration_us.count()))
<< " us" << std::endl;
return(retVal);
}
旧戴尔的典型输出。
Fri Jun 30 15:30:13 2017
--------------------------------------------------------------
10 second measure of 10 threads, 1 PPLSem_t Q6::main()
output: ./Q6.txt
block threads at crit sect
createAndActivateThreads() .0.1.2.3.4.5.6.7.8.9 (1,002,120 us)
releaseThreadsAndWait 9 8 7 6 5 4 3 2 1 0
join threads . . . . . . . . . . (2,971 us)
31.07730700 M 'thread context switch' events in 10,021,447 us
3.101079814 M 'thread context switch' events per second
322.4683207 n sec per 'thread context switch' event
each thread run count:
3,182,496 3,252,929 3,245,473 3,150,344 3,411,918 2,936,982 2,978,690 3,029,319 3,004,926 2,884,230
10.2406 10.4672 10.4432 10.1371 10.9788 9.45057 9.58478 9.74769 9.6692 9.28082 (% of total)
total : 31,077,307 note variability -- min : 9.28082% max : 10.9788%
--------------------------------------------------------------
writing Thread ID sequence of 31,077,307 values to ./Q6.txt
complete: 3,025,289 us
--------------------------------------------------------------
Stack Size: 8,720,384 [of 'main()' by pthread_attr_getstacksize]
--------------------------------------------------------------
3 second measure of lock()/unlock() (no collision)
173.2359360 M 'sem lock()+unlock()' events in 3,902,491 us
44.39111737 M 'sem lock()+unlock()' events per second
22.52702926 n sec per 'sem lock()+unlock()' event
FINI 18,957,304 us
Q6.txt行的样本长度为100个字符。
AABABABABAAAAAAAAAAAABBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
最后几行
BJBJBJBJBJBJBJBJBBHHHHHHHHHHHHHHHHHBBAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABAAAAAAA
AAAAAAAAAAAAAAAAAAAAAABABABABAABABBAAAAAAAAAAAAAAAAAAAAAAAAAAAAABABABBGGGGGGGGGGGGGGGBGBGBGBGBGBGBGBG
BGBGBGBGBGBGBGBGBGBBGBGBGBGBGBGBGBBHHHHHHHHHHHHHHHHBHBHBHBHBHBHBHBHBHBHBHBHBHBHBHBBHBHBHBHBBJJJJJJJJJ
JJJJJJJJJBBJBBBJBJBJBJBJBJBBJBJBJBJBJBJBJBJBJBBEEEEEEEEEEEEEEEEEBEBEBEBEBEBEBEBEBEBEBEBEBEBEBBEBEBEBE
BEBEBEBEBEBEBEBEBEBEBEBEBEBEBBEBEBEBBBBEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEBEBBEBEBEBEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEBEBEBEBEEBEBEBEBEBBIIIIIIIIIIIIIIIBBIIIBIBBFFFFFFFFFFFFFFFBBFFBBFBFBFBFBFFBBGGGGGGGGGGGGGGGGG
BBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGBGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
GGBCIHFJDAE
答案 1 :(得分：1)
您引用的所有C函数都可以通过以下方式访问 直接包括。
谢谢，我知道这个事实，但任务是避免C和使用 C ++尽可能。
我的C ++代码中没有C代码，只是调用extern“C” Linux提供的功能。没有单独的C ++ Linux集 函数调用。 Linux API（到os服务）由 C库和头文件。我知道无法避免或解决 Linux API，所以也许我不知道你在暗示/问什么。
你可以解释一下吗？我通过重复一些动作1至10秒来测量持续时间， 并计算循环完成的次数。
考虑代码段
{
uint64_t microsecStart = getSystemMicroSecond();
//convert linear time to broken-down/calendar time
local_tm = *localtime_r (&linear_time, &local_tm);
uint64_t microsecDuration = getSystemMicroSecond() - microsecStart;
}
此操作通常太快，无法以这种简单的方式进行测量， 基本上是一个delta-microsecond，转换将在a之前结束 微秒可能会改变。
为了快速测量某些东西，我们围绕着它的动作 兴趣，并计算循环，并在3秒后开出。
uint64_t microsecStart = getSystemMicroSecond();
uint32_t loopCount = 0;
time_t t0 = time(0) + 3; // loop for < 3 seconds
do
{
//convert linear time to broken-down/calendar time
local_tm = *localtime_r (&linear_time, &local_tm);
time_t t1 = time(0);
if(t1 != t0) break;
loopCount += 1;
} while(1);
uint64_t microsecDuration = getSystemMicroSecond() - microsecStart;
在这个循环中，时间（0）功能非常快。
所以时间（0）不会显着延长测量值。
但足够快，可以准确测量当地持续时间
当这些旋转完成时，测试创建了一个loopCount，并且a 循环外的持续时间测量提供更一致的测量 持续时间...，然后我们可以计算'平均' 每个事件的持续时间。
您是否忽略了进程运行的时间？
是。因为我知道上下文切换是2阶 比函数调用慢，这并不困难 最小化线程活动没有/最小影响 关于测量。
与切换时间相比，它是否很小？
在此测试中，线程递增一个数字，测试一个标志，然后动作 作为一个好邻居（即这些线程将处理器交给了 尽快）。这些小动作对于这些微不足道的行为微不足道 上下文切换的成本。
我6岁的戴尔的数字是3个数量级的差异。
简单函数调用：即时间（0）＆lt; 75 e-9秒
线程上下文切换＆lt; 15 e-6秒 用信号量强制执行
其他活动可以影响结果，但我认为 微不足道的。我的每个“螺纹开关和我的14 us的结果 信号量发送“比最好的结果更长，但不是 足够长的时间来影响我的设计决策。有可能 改善这种测量，但我买不起硬件。
Linux提供了一些线程或任务优先级的想法，但我没有 探索了他们。当我认真寻找“更好”的测量时， 我想我会断开以太网，关闭任何繁忙的工作......但是 我没有运行编译，也没有复制文件，也没有运行备份 当我测量时，任何明显的cpu周期消费者。机器是 基本上空闲。只是时钟滴答，定时器到期，内存 刷新，以及其他一些必须继续的事情。
为了好玩或兴趣，您可以启动系统监视器实用程序， 单击％CPU标签1或2次，并将最繁忙的任务带到 顶部......你应该发现最繁忙的任务是ta-da：系统 监控可能是2个cpu之一的3％。所有其他任务都是 基本上等待某事，并触发0％的负载。
最后你可能会这样想......
你正在编写一个在非典型机器上运行的程序吗？ 或者你的目标是否与你的开发机器相似？你打算关闭中断吗？ i / o频道？以太网？控制 优先？或者你的目标是否有用。
恕我直言，系统运行时我的有用（linux）系统中的运行任务 一般来说，除了等待我的下一次击键之外什么都不做 在大多数10秒的测试中什么都不做。
我认为这些努力中最重要的一点是：
function calls are more than 100x faster than context switches.