Merge pull request #18019 from king-11/qt_sys_calls

[GSOC] Qthread Select

[PR by @king-11 - reviewed by @krishnadey30 and @mppf; tested,merged by @mppf]

conditional compilation of `qt_select` for providing in a method to keep original task unblocked when observing for IO.

Prior to `qt_select` call `select` and block for 64ms which allows instantaneous connections to be established
without timing out.

Signed-off-by: Lakshya Singh <lakshay.singh1108@gmail.com>

runtime/src/qio/sys.c

@@ -92,7 +92,10 @@
 
 #endif
 
-
+// to use qthread sys calls when available
+#ifdef QTHREAD_VERSION
+#include <qthread/qt_syscalls.h>
+#endif
 
 // Should be available in sys_xsi_strerror_r.c
 extern int sys_xsi_strerror_r(int errnum, char* buf, size_t buflen);
@@ -1427,7 +1430,8 @@ err_t sys_accept(fd_t sockfd, sys_sockaddr_t* addr_out, fd_t* fd_out)
 
   STARTING_SLOW_SYSCALL;
 
-  got = accept(sockfd, (struct sockaddr*) & addr_out->addr, &addr_len);
+  got = accept(sockfd, (struct sockaddr *)&addr_out->addr, &addr_len);
+
   if( got != -1 ) {
     if( addr_len > (socklen_t) sizeof(sys_sockaddr_storage_t) ) {
       fprintf(stderr, "Warning: address truncated in sys_accept\n");
@@ -1471,7 +1475,8 @@ err_t sys_connect(fd_t sockfd, const sys_sockaddr_t* addr)
 
   STARTING_SLOW_SYSCALL;
 
-  got = connect(sockfd, (const struct sockaddr*) & addr->addr, addr->len);
+  got = connect(sockfd, (const struct sockaddr *)&addr->addr, addr->len);
+
   if( got != -1 ) {
     err_out = 0;
   } else {
@@ -1862,45 +1867,62 @@ err_t sys_socketpair(int domain, int type, int protocol, fd_t* sockfd_out_a, fd_
 extern void chpl_task_yield(void);
 
 err_t sys_select(int nfds, fd_set* readfds, fd_set* writefds, fd_set* exceptfds, struct timeval* timeout, int* nset) {
-
   int got_nset;
   err_t err_out = 0;
-  struct timeval deadline;
-  struct timeval now;
-  struct timeval real_timeout;
-  long wait_usec = 5;
-
-  if (timeout != NULL) {
-    gettimeofday(&deadline, NULL);
-    deadline.tv_sec += timeout->tv_sec;
-    deadline.tv_usec += timeout->tv_usec;
-    if (deadline.tv_usec > 1000000) {
-      deadline.tv_sec++;
-      deadline.tv_usec -= 1000000;
-    }
-  } else if (timeout->tv_sec == 0) {
-    if (timeout->tv_usec < wait_usec)
-      wait_usec = timeout->tv_usec;
+
+  struct timeval first_timeout;
+  struct timeval second_timeout = {0};
+  if(timeout != NULL) {
+    second_timeout = *timeout;
   }
 
-  real_timeout.tv_sec = 0;
-  real_timeout.tv_usec = wait_usec;
+  first_timeout.tv_sec = 0;
+  // 64 milliseconds allows instantaneous connections whereas 32000 doesn't
+  // and is small enough to not block process for longtime
+  first_timeout.tv_usec = 64000;
 
-  while (1) {
-    // It would be nicer if the tasking layer supported a select
-    // call and knew to wait in the select call if no task was waiting
-    got_nset = select(nfds, readfds, writefds, exceptfds, &real_timeout);
-    if (got_nset == -1) err_out = errno; // save error
-    if (got_nset != 0) break; // exit loop if something happened
-#ifndef CHPL_RT_UNIT_TEST
-    chpl_task_yield();
-#endif
-    gettimeofday(&now, NULL);
-    if (now.tv_sec > deadline.tv_sec ||
-        (now.tv_sec == deadline.tv_sec && now.tv_usec > deadline.tv_usec))
-      break;
+  // calculate available timeout
+  if (timeout != NULL){
+    first_timeout.tv_usec = (second_timeout.tv_usec > 64000 || second_timeout.tv_sec >= 1) ? 64000 : second_timeout.tv_usec;
+
+    second_timeout.tv_usec -= first_timeout.tv_usec;
+    if(second_timeout.tv_usec < 0){
+      second_timeout.tv_sec -= 1;
+      second_timeout.tv_usec += 1000000;
+    }
   }
 
+  // create new fd_sets otherwise original will be overwritten
+  fd_set temp_readfds, temp_writefds, temp_exceptfds;
+  FD_ZERO(&temp_readfds);
+  FD_ZERO(&temp_writefds);
+  FD_ZERO(&temp_exceptfds);
+  if(readfds != NULL)
+    temp_readfds = *readfds;
+  if(writefds != NULL)
+    temp_writefds = *writefds;
+  if(exceptfds != NULL)
+    temp_exceptfds = *exceptfds;
+
+  got_nset = select(nfds, &temp_readfds, &temp_writefds, &temp_exceptfds, &first_timeout);
+  if (got_nset == -1) err_out = errno; // save error
+
+  // check for error/success else check if first_timeout subtraced all the timeout.
+  if(got_nset != 0 || (timeout != NULL && second_timeout.tv_sec == 0 && second_timeout.tv_usec == 0)){
+    *nset = got_nset;
+    return err_out;
+  }
+
+  struct timeval* second_timeout_ptr = NULL;
+  if (timeout != NULL)
+    second_timeout_ptr = &second_timeout;
+
+#if defined(QTHREAD_VERSION) && !defined(CHPL_RT_UNIT_TEST)
+  got_nset = qt_select(nfds, readfds, writefds, exceptfds, second_timeout_ptr);
+#else
+  got_nset = select(nfds, readfds, writefds, exceptfds, second_timeout_ptr);
+#endif
+  if (got_nset == -1) err_out = errno; // save error
   *nset = got_nset;
   return err_out;
 }