Create the waiting selector only after the first wait

Sometimes there is no need to wait at all, if the generator exits on the
first result. It happens especially in copy.

diff --git a/psycopg3/psycopg3/waiting.py b/psycopg3/psycopg3/waiting.py
index ba6e005d54ac47dfd2c9ad4448170dd49e34a58d..b0f87474b45422bdb8c5d34a403384a335d27bfa 100644 (file)
--- a/psycopg3/psycopg3/waiting.py
+++ b/psycopg3/psycopg3/waiting.py
@@ -48,9 +48,9 @@ def wait_selector(
     Consume *gen*, scheduling `fileno` for completion when it is reported to
     block. Once ready again send the ready state back to *gen*.
     """
-    sel = DefaultSelector()
     try:
         s = next(gen)
+        sel = DefaultSelector()
         while 1:
             sel.register(fileno, s)
             ready = None
@@ -78,9 +78,9 @@ def wait_conn(gen: PQGenConn[RV], timeout: Optional[float] = None) -> RV:
     Behave like in `wait()`, but take the fileno to wait from the generator
     itself, which might change during processing.
     """
-    sel = DefaultSelector()
     try:
         fileno, s = next(gen)
+        sel = DefaultSelector()
         while 1:
             sel.register(fileno, s)
             ready = None
@@ -214,13 +214,14 @@ def wait_epoll(
 
     See also: https://linux.die.net/man/2/epoll_ctl
     """
-    epoll = select.epoll()
     if timeout is None or timeout < 0:
         timeout = 0
     else:
         timeout = int(timeout * 1000.0)
+
     try:
         s = next(gen)
+        epoll = select.epoll()
         evmask = poll_evmasks[s]
         epoll.register(fileno, evmask)
         while 1: