[input] try to use CLOCK_MONOTONIC for condvar

By default, Pthread condition variables use the wretched
CLOCK_REALTIME for pthread_cond_timedwait(). We reaaaaaaly
want it to use CLOCK_MONOTONIC instead. Where supported,
use pthread_condvar_setclock() to initialize the input
condvar with CLOCK_MONOTONIC, since every other operation
we perform is clocked against it. Closes #2291.

src/lib/in.c

@@ -1385,6 +1385,24 @@ getpipes(ipipe pipes[static 2]){
   return 0;
 }
 
+// attempt to set up a pthread_condattr_t such that pthread_cond_timedwait()
+// uses CLOCK_MONOTONIC rather than CLOCK_REALTIME. unfortunately, this isn't
+// available on all operating systems. return success so long as we can
+// initialize the condattr_t; it does not imply successful clock selection =\.
+static int
+prep_condattr(pthread_condattr_t* cattr){
+  int e;
+  if( (e = pthread_condattr_init(cattr)) ){
+    logerror("couldn't initialize condattr (%s)\n", strerror(e));
+    return -1;
+  }
+  // remember, return success even if this doesn't fly
+  if( (e = pthread_condattr_setclock(cattr, CLOCK_MONOTONIC)) ){
+    logwarn("warning: couldn't set CLOCK_MONOTONIC for condvar (%s)\n", strerror(e));
+  }
+  return 0;
+}
+
 static inline inputctx*
 create_inputctx(tinfo* ti, FILE* infp, int lmargin, int tmargin, int rmargin,
                 int bmargin, ncsharedstats* stats, unsigned drain,
@@ -1396,52 +1414,56 @@ create_inputctx(tinfo* ti, FILE* infp, int lmargin, int tmargin, int rmargin,
       i->isize = BUFSIZ;
       if( (i->inputs = malloc(sizeof(*i->inputs) * i->isize)) ){
         if(pthread_mutex_init(&i->ilock, NULL) == 0){
-          if(pthread_cond_init(&i->icond, NULL) == 0){
-            if(pthread_mutex_init(&i->clock, NULL) == 0){
-              if(pthread_cond_init(&i->ccond, NULL) == 0){
-                if((i->stdinfd = fileno(infp)) >= 0){
-                  if( (i->initdata = malloc(sizeof(*i->initdata))) ){
-                    if(getpipes(i->readypipes) == 0){
-                      memset(&i->amata, 0, sizeof(i->amata));
-                      if(prep_special_keys(i) == 0){
-                        if(set_fd_nonblocking(i->stdinfd, 1, &ti->stdio_blocking_save) == 0){
-                          i->termfd = tty_check(i->stdinfd) ? -1 : get_tty_fd(infp);
-                          memset(i->initdata, 0, sizeof(*i->initdata));
-			                    i->initdata->qterm = ti->qterm;
-                          i->iread = i->iwrite = i->ivalid = 0;
-                          i->cread = i->cwrite = i->cvalid = 0;
-                          i->initdata_complete = NULL;
-                          i->stats = stats;
-                          i->ti = ti;
-                          i->stdineof = 0;
+          pthread_condattr_t condattr;
+          if(prep_condattr(&condattr) == 0){
+            if(pthread_cond_init(&i->icond, &condattr) == 0){
+              if(pthread_mutex_init(&i->clock, NULL) == 0){
+                if(pthread_cond_init(&i->ccond, &condattr) == 0){
+                  if((i->stdinfd = fileno(infp)) >= 0){
+                    if( (i->initdata = malloc(sizeof(*i->initdata))) ){
+                      if(getpipes(i->readypipes) == 0){
+                        memset(&i->amata, 0, sizeof(i->amata));
+                        if(prep_special_keys(i) == 0){
+                          if(set_fd_nonblocking(i->stdinfd, 1, &ti->stdio_blocking_save) == 0){
+                            i->termfd = tty_check(i->stdinfd) ? -1 : get_tty_fd(infp);
+                            memset(i->initdata, 0, sizeof(*i->initdata));
+                            i->initdata->qterm = ti->qterm;
+                            i->iread = i->iwrite = i->ivalid = 0;
+                            i->cread = i->cwrite = i->cvalid = 0;
+                            i->initdata_complete = NULL;
+                            i->stats = stats;
+                            i->ti = ti;
+                            i->stdineof = 0;
 #ifdef __MINGW64__
-                          i->stdinhandle = ti->inhandle;
+                            i->stdinhandle = ti->inhandle;
 #endif
-                          i->ibufvalid = 0;
-                          i->linesigs = linesigs_enabled;
-                          i->tbufvalid = 0;
-                          i->midescape = 0;
-                          i->lmargin = lmargin;
-                          i->tmargin = tmargin;
-                          i->rmargin = rmargin;
-                          i->bmargin = bmargin;
-                          i->drain = drain;
-                          i->failed = false;
-                          logdebug("input descriptors: %d/%d\n", i->stdinfd, i->termfd);
-                          return i;
+                            i->ibufvalid = 0;
+                            i->linesigs = linesigs_enabled;
+                            i->tbufvalid = 0;
+                            i->midescape = 0;
+                            i->lmargin = lmargin;
+                            i->tmargin = tmargin;
+                            i->rmargin = rmargin;
+                            i->bmargin = bmargin;
+                            i->drain = drain;
+                            i->failed = false;
+                            logdebug("input descriptors: %d/%d\n", i->stdinfd, i->termfd);
+                            return i;
+                          }
                         }
+                        input_free_esctrie(&i->amata);
                       }
-                      input_free_esctrie(&i->amata);
+                      endpipes(i->readypipes);
                     }
-                    endpipes(i->readypipes);
+                    free(i->initdata);
                   }
-                  free(i->initdata);
+                  pthread_cond_destroy(&i->ccond);
                 }
-                pthread_cond_destroy(&i->ccond);
+                pthread_mutex_destroy(&i->clock);
               }
-              pthread_mutex_destroy(&i->clock);
+              pthread_cond_destroy(&i->icond);
             }
-            pthread_cond_destroy(&i->icond);
+            pthread_condattr_destroy(&condattr);
           }
           pthread_mutex_destroy(&i->ilock);
         }