ncurses在多線程應用程序

Question

我有一個多線程的應用程序，它使用單個線程上的ncurses向用戶報告信息。我的代碼基本上是這樣的：

const unsigned int  refresh_cycle = 180; 
unsigned int   refresh_count = refresh_cycle; 

while(killswitch != 1) { 

    if (refresh_count >= refresh_cycle) { 
     // critical section which obtains some data worked on by a thread. only does this once every refresh cycle times 
     // mtx lock, fetch, mtx unlock 
     refresh_count = 0; 
    } 
    refresh_count++; 

    // get input 

    // draw some stuff 

    // refresh 
} 

我注意到的是，ncurses的窗口得到刷新很多很多倍。對於一個只需15-30次刷新即可完成的用戶來說，這種方式實際上是非常需要的。

但現在我擔心這可能會從正在工作的線程中「偷走」不必要的處理能力。這是一個合理的斷言嗎？

我應該使用usleep()構建一種幀限制器嗎？還是會過度使用？

Answer 1

根據評論，如果在刷新之間需要處理用戶輸入，那麼最簡單的方法可能是在STDIN_FILENO上調用select()並使用適當的小超時。當select()返回時，要麼是因爲有用戶輸入，要麼是因爲超時，請在該點進行刷新。

下面是一個示例，可讓您瞭解如何設置它，並顯示select()何時返回以及發生多少次，以便您可以直觀地看到發生了什麼。嘗試讓它坐下並運行一段時間，然後嘗試按住一個鍵，然後觀察select() has returned [n] times消息在每種情況下的行爲。在代碼中的註釋說明了發生的事情：

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <errno.h> 
#include <unistd.h> 
#include <time.h> 
#include <sys/select.h> 
#include <ncurses.h> 

/* struct to store curses info for cleanup */ 

struct curinfo { 
    WINDOW * main_window; 
    int old_cursor; 
}; 

/* curses helper functions */ 

void start_curses(struct curinfo * info); 
void stop_curses(struct curinfo * info); 

/* main function */ 

int main(int argc, char * argv[]) 
{ 
    /* Set default timeout */ 

    int secs = 0; 
    int usecs = 500000; 

    /* Set timeout based on command line args, if provided */ 

    if (argc > 1) { 
     if (!strcmp(argv[1], "veryshort")) { 
      secs = 0; 
      usecs = 200000; 
     } 
     else if (!strcmp(argv[1], "short")) { 
      secs = 1; 
      usecs = 0; 
     } 
     else if (!strcmp(argv[1], "medium")) { 
      secs = 2; 
      usecs = 0; 
     } 
     else if (!strcmp(argv[1], "long")) { 
      secs = 5; 
      usecs = 0; 
     } 
    } 

    struct curinfo cinfo; 
    start_curses(&cinfo); 

    int input = '0';  /* Set to something printable */ 
    int num_sel = 0;  /* Number of times select() has returned */ 

    while (input != 'q' && input != 'Q') { 

     /* Output messages */ 

     mvprintw(3, 3, "select() has returned %d times", num_sel); 
     mvprintw(4, 3, "Last character input was %c", input); 
     mvprintw(5, 3, "Press 'q' to quit"); 
     refresh(); 

     /* select() modifies the fd_sets passed to it, 
     * so zero and set them prior to each call.  */ 

     fd_set fds; 
     FD_ZERO(&fds); 
     FD_SET(STDIN_FILENO, &fds); 

     /* Same deal for the struct timeval, select() may 
     * modify it, it may not, so recreate to be portable. */ 

     struct timeval tv; 
     tv.tv_sec = secs; 
     tv.tv_usec = usecs; 

     /* Store the return so we can check it */ 

     int status = select(STDIN_FILENO + 1, &fds, NULL, NULL, &tv); 

     /* Check for error */ 

     if (status == -1) { 

      /* select() returned with an error. */ 

      if (errno != EINTR) { 

       /* If interrupted by a signal, no problem, 
       * keep going. Otherwise, let's just quit. */ 

       stop_curses(&cinfo); 
       perror("error calling select()"); 
       return EXIT_FAILURE; 
      } 
     } 
     else if (FD_ISSET(STDIN_FILENO, &fds)) { 

      /* Only call getch() if input is ready. 
      * getch() will not block when we do it this way. */ 

      if ((input = getch()) == ERR) { 
       stop_curses(&cinfo); 
       fprintf(stderr, "ERR returned from getch()\n"); 
       return EXIT_FAILURE; 
      } 
     } 

     /* Increment number of times select() has returned */ 

     ++num_sel; 
    } 

    stop_curses(&cinfo); 

    return 0; 
} 

/* Starts curses and populates the passed struct */ 

void start_curses(struct curinfo * info) 
{ 
    if ((info->main_window = initscr()) == NULL) { 
     fprintf(stderr, "Error calling initscr()\n"); 
     exit(EXIT_FAILURE); 
    } 

    keypad(stdscr, TRUE); 
    timeout(0); 
    raw(); 
    nonl(); 
    noecho(); 
    info->old_cursor = curs_set(0); 
    refresh(); 
} 

/* Stops curses and cleans up */ 

void stop_curses(struct curinfo * info) 
{ 
    delwin(info->main_window); 
    curs_set(info->old_cursor); 
    endwin(); 
    refresh(); 
}