From db993006c341f476e80cf7f1aba59081d2947ab3 Mon Sep 17 00:00:00 2001
From: "Eric S. Raymond" <esr@thyrsus.com>
Date: Mon, 3 Oct 2011 10:45:29 -0400
Subject: First cut at implementing waiting test for shm export.

Timeout argument is presently ignored.
---
 libgps.h      |  6 +++---
 libgps.xml    |  2 +-
 libgps_core.c |  8 +++++++-
 libgps_shm.c  | 14 ++++++++++++++
 shmexport.c   |  5 +++--
 5 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/libgps.h b/libgps.h
index 5901ea89..cc5b5e70 100644
--- a/libgps.h
+++ b/libgps.h
@@ -37,12 +37,12 @@ extern int gps_sock_stream(struct gps_data_t *, unsigned int, /*@null@*/void *);
 extern const char /*@observer@*/ *gps_sock_data(const struct gps_data_t *);
 extern int gps_sock_mainloop(struct gps_data_t *, int,
 			      void (*)(struct gps_data_t *));
-extern int gps_shm_mainloop(struct gps_data_t *, int,
-			      void (*)(struct gps_data_t *));
-
 extern int gps_shm_open(/*@out@*/struct gps_data_t *);
 extern void gps_shm_close(struct gps_data_t *);
+extern bool gps_shm_waiting(const struct gps_data_t *, int);
 extern int gps_shm_read(struct gps_data_t *);
+extern int gps_shm_mainloop(struct gps_data_t *, int,
+			      void (*)(struct gps_data_t *));
 
 extern int gps_dbus_open(struct gps_data_t *);
 extern int gps_dbus_mainloop(struct gps_data_t *, int,
diff --git a/libgps.xml b/libgps.xml
index 059c7d01..2f5d09d5 100644
--- a/libgps.xml
+++ b/libgps.xml
@@ -150,7 +150,7 @@ error condition. This function is a convenience wrapper around a
 <citerefentry><refentrytitle>select</refentrytitle><manvolnum>2</manvolnum></citerefentry>
 call, and zeros <varname>errno</varname> on entry; you can test
 <varname>errno</varname> after exit to get more information about
-error conditions.</para>
+error conditions. The timeout value is in nanoseconds.</para>
 
 <para><function>gps_unpack()</function> parses JSON from the argument
 buffer into the target of the session structure pointer argument.
diff --git a/libgps_core.c b/libgps_core.c
index 1759e6a5..687b8b82 100644
--- a/libgps_core.c
+++ b/libgps_core.c
@@ -205,8 +205,14 @@ bool gps_waiting(const struct gps_data_t *gpsdata CONDITIONALLY_UNUSED, int time
     /* this is bogus, but I can't think of a better solution yet */
     bool waiting = true;
 
+#ifdef SHM_EXPORT_ENABLE
+    if ((intptr_t)(gpsdata->gps_fd) == SHM_PSEUDO_FD)
+	waiting = gps_shm_waiting(gpsdata, timeout);
+#endif /* SHM_EXPORT_ENABLE */
+
 #ifdef SOCKET_EXPORT_ENABLE
-    waiting = gps_sock_waiting(gpsdata, timeout);
+    if ((intptr_t)(gpsdata->gps_fd) >= 0)
+	waiting = gps_sock_waiting(gpsdata, timeout);
 #endif /* SOCKET_EXPORT_ENABLE */
 
     return waiting;
diff --git a/libgps_shm.c b/libgps_shm.c
index b28b13a7..1ea25c67 100644
--- a/libgps_shm.c
+++ b/libgps_shm.c
@@ -31,6 +31,7 @@ PERMISSIONS
 struct privdata_t
 {
     void *shmseg;
+    int tick;
 };
 /*@+matchfields@*/
 
@@ -65,6 +66,18 @@ int gps_shm_open(/*@out@*/struct gps_data_t *gpsdata)
     return 0;
 }
 
+bool gps_shm_waiting(const struct gps_data_t *gpsdata, int timeout UNUSED)
+/* check to see if new dayta has been written */
+{
+    volatile struct shmexport_t *shared = (struct shmexport_t *)PRIVATE(gpsdata)->shmseg;
+    bool newdata;
+
+    barrier();
+    newdata = (shared->bookend1 == shared->bookend2 && shared->bookend1 > PRIVATE(gpsdata)->tick + timeout);
+    barrier();
+    return newdata;
+}
+
 int gps_shm_read(struct gps_data_t *gpsdata)
 /* read an update from the shared-memory segment */
 {
@@ -104,6 +117,7 @@ int gps_shm_read(struct gps_data_t *gpsdata)
 			 (void *)&noclobber, 
 			 sizeof(struct gps_data_t));
 	    /*@i1@*/gpsdata->privdata = private_save;
+	    PRIVATE(gpsdata)->tick = after;
 	    if ((gpsdata->set & REPORT_IS)!=0) {
 		if (gpsdata->fix.mode >= 2)
 		    gpsdata->status = STATUS_FIX;
diff --git a/shmexport.c b/shmexport.c
index 8e2cf190..5959b581 100644
--- a/shmexport.c
+++ b/shmexport.c
@@ -22,6 +22,7 @@ PERMISSIONS
 #include <sys/shm.h>
 
 #include "gpsd.h"
+#include "libgps.h" /* for SHM_PSEUDO_FD */
 
 #ifdef SHM_EXPORT_ENABLE
 
@@ -84,9 +85,9 @@ void shm_update(struct gps_context_t *context, struct gps_data_t *gpsdata)
 	       sizeof(struct gps_data_t)); 
 	barrier();
 #ifndef USE_QT
-	shared->gpsdata.gps_fd = -1;
+	shared->gpsdata.gps_fd = SHM_PSEUDO_FD;
 #else
-	shared->gpsdata.gps_fd = (void *)(intptr_t)-1;
+	shared->gpsdata.gps_fd = (void *)(intptr_t)SHM_PSEUDO_FD;
 #endif /* USE_QT */
 	barrier();
 	shared->bookend1 = tick;
-- 
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