Use unnamed POSIX semaphores on Cygwin.

Testing on CI showed that Cygwin's semctl() can fail with EAGAIN
(possibly due to resource limits in cygserver that could be tuned, not
examined).  Switch to so-called POSIX semaphores instead, which don't
seem to fail in that way (possibly due to a more direct implementation
using Windows semaphore primitives instead of talking to cygserver,
based on a cursory glance at the source).

Other known problems still prevent PostgreSQL from running on Cygwin
without random crashes, but this rarer problem was noticed while
testing.

Discussion: https://postgr.es/m/CA%2BhUKG%2BQ6DU4Ov9LrvUyDcF3oHS4KMRVSKmVGaeePq-kOyG9gA%40mail.gmail.com

diff --git a/meson.build b/meson.build
index 8999170b4d2cb1cc8830144d6282a81237a23817..45fb9dd616eea0d1396b3e0a983b3f7b7a154e09 100644 (file)
--- a/meson.build
+++ b/meson.build
@@ -211,6 +211,7 @@ if host_system == 'aix'
   memset_loop_limit = 0
 
 elif host_system == 'cygwin'
+  sema_kind = 'unnamed_posix'
   cppflags += '-D_GNU_SOURCE'
   dlsuffix = '.dll'
   mod_link_args_fmt = ['@0@']

diff --git a/src/template/cygwin b/src/template/cygwin
index 3f42e2f8b69c227fec0518acb7289558521d821b..4a03707a8566ce49df1fbe5e44e98338793223b0 100644 (file)
--- a/src/template/cygwin
+++ b/src/template/cygwin
@@ -1,5 +1,10 @@
 # src/template/cygwin
 
+# Prefer unnamed POSIX semaphores if available, unless user overrides choice
+if test x"$PREFERRED_SEMAPHORES" = x"" ; then
+  PREFERRED_SEMAPHORES=UNNAMED_POSIX
+fi
+
 SRCH_LIB="/usr/local/lib"
 
 # This is required for ppoll(2), and perhaps other things