Make it easier to choose the used waiting primitive in unix_latch.c.

This allows for easier testing of the different primitives; in
preparation for adding a new primitive.

Discussion: 20160114143931.GG10941@awork2.anarazel.de
Reviewed-By: Robert Haas

diff --git a/src/backend/port/unix_latch.c b/src/backend/port/unix_latch.c
index 9f8b8d54f079ae6abbcb70d0dafce82f997748fc..e7be7ec11797d720ba17566d9e54a9a125ce2f15 100644 (file)
--- a/src/backend/port/unix_latch.c
+++ b/src/backend/port/unix_latch.c
@@ -56,6 +56,22 @@
 #include "storage/pmsignal.h"
 #include "storage/shmem.h"
 
+/*
+ * Select the fd readiness primitive to use. Normally the "most modern"
+ * primitive supported by the OS will be used, but for testing it can be
+ * useful to manually specify the used primitive.  If desired, just add a
+ * define somewhere before this block.
+ */
+#if defined(LATCH_USE_POLL) || defined(LATCH_USE_SELECT)
+/* don't overwrite manual choice */
+#elif defined(HAVE_POLL)
+#define LATCH_USE_POLL
+#elif HAVE_SYS_SELECT_H
+#define LATCH_USE_SELECT
+#else
+#error "no latch implementation available"
+#endif
+
 /* Are we currently in WaitLatch? The signal handler would like to know. */
 static volatile sig_atomic_t waiting = false;
 
@@ -215,10 +231,10 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
                                cur_time;
        long            cur_timeout;
 
-#ifdef HAVE_POLL
+#if defined(LATCH_USE_POLL)
        struct pollfd pfds[3];
        int                     nfds;
-#else
+#elif defined(LATCH_USE_SELECT)
        struct timeval tv,
                           *tvp;
        fd_set          input_mask;
@@ -248,7 +264,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
                Assert(timeout >= 0 && timeout <= INT_MAX);
                cur_timeout = timeout;
 
-#ifndef HAVE_POLL
+#ifdef LATCH_USE_SELECT
                tv.tv_sec = cur_timeout / 1000L;
                tv.tv_usec = (cur_timeout % 1000L) * 1000L;
                tvp = &tv;
@@ -258,7 +274,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
        {
                cur_timeout = -1;
 
-#ifndef HAVE_POLL
+#ifdef LATCH_USE_SELECT
                tvp = NULL;
 #endif
        }
@@ -292,16 +308,10 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
                }
 
                /*
-                * Must wait ... we use poll(2) if available, otherwise select(2).
-                *
-                * On at least older linux kernels select(), in violation of POSIX,
-                * doesn't reliably return a socket as writable if closed - but we
-                * rely on that. So far all the known cases of this problem are on
-                * platforms that also provide a poll() implementation without that
-                * bug.  If we find one where that's not the case, we'll need to add a
-                * workaround.
+                * Must wait ... we use the polling interface determined at the top of
+                * this file to do so.
                 */
-#ifdef HAVE_POLL
+#if defined(LATCH_USE_POLL)
                nfds = 0;
                if (wakeEvents & (WL_SOCKET_READABLE | WL_SOCKET_WRITEABLE))
                {
@@ -397,8 +407,16 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
                                        result |= WL_POSTMASTER_DEATH;
                        }
                }
-#else                                                  /* !HAVE_POLL */
+#elif defined(LATCH_USE_SELECT)
 
+               /*
+                * On at least older linux kernels select(), in violation of POSIX,
+                * doesn't reliably return a socket as writable if closed - but we
+                * rely on that. So far all the known cases of this problem are on
+                * platforms that also provide a poll() implementation without that
+                * bug.  If we find one where that's not the case, we'll need to add a
+                * workaround.
+                */
                FD_ZERO(&input_mask);
                FD_ZERO(&output_mask);
 
@@ -478,7 +496,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
                                        result |= WL_POSTMASTER_DEATH;
                        }
                }
-#endif   /* HAVE_POLL */
+#endif   /* LATCH_USE_SELECT */
 
                /* If we're not done, update cur_timeout for next iteration */
                if (result == 0 && (wakeEvents & WL_TIMEOUT))
@@ -491,7 +509,7 @@ WaitLatchOrSocket(volatile Latch *latch, int wakeEvents, pgsocket sock,
                                /* Timeout has expired, no need to continue looping */
                                result |= WL_TIMEOUT;
                        }
-#ifndef HAVE_POLL
+#ifdef LATCH_USE_SELECT
                        else
                        {
                                tv.tv_sec = cur_timeout / 1000L;