Switch sequence comparisons to handle 32-bit sequence number wrap.

Create a macro, XCB_SEQUENCE_COMPARE, that accepts two sequence numbers and
a comparison operator and correctly handles 32-bit wrap around.
Rewrite all ordered sequence number comparisons to use this macro.
Also, caught one error where a sequence was stored in a signed int variable.
Push out a GetInputFocus request when the sequence number does wrap at 32
bits so that applications cannot see sequence 0 (as that is an error
indicator).

3 files changed, 39 insertions, 15 deletions

diff --git a/src/xcb_in.c b/src/xcb_in.c
index 3bf54f3..6433f0e 100644
--- a/src/xcb_in.c
+++ b/src/xcb_in.c
@@ -91,11 +91,11 @@ static int read_packet(XCBConnection *c)
     /* Compute 32-bit sequence number of this packet. */
     if((genrep.response_type & 0x7f) != XCBKeymapNotify)
     {
-        int lastread = c->in.request_read;
+        unsigned int lastread = c->in.request_read;
         c->in.request_read = (lastread & 0xffff0000) | genrep.sequence;
-        if(c->in.request_read < lastread)
+        if(XCB_SEQUENCE_COMPARE(c->in.request_read, <, lastread))
             c->in.request_read += 0x10000;
-        if(c->in.request_read > c->in.request_expected)
+        if(XCB_SEQUENCE_COMPARE(c->in.request_read, >, c->in.request_expected))
             c->in.request_expected = c->in.request_read;
 
         if(c->in.request_read != lastread)
@@ -111,7 +111,8 @@ static int read_packet(XCBConnection *c)
         if(genrep.response_type != XCBReply) /* error or event */
             c->in.request_completed = c->in.request_read; /* XXX: does event/error imply no more replies? */
 
-        while(c->in.pending_replies && c->in.pending_replies->request <= c->in.request_completed)
+        while(c->in.pending_replies && 
+	      XCB_SEQUENCE_COMPARE (c->in.pending_replies->request, <=, c->in.request_completed))
         {
             pending_reply *oldpend = c->in.pending_replies;
             c->in.pending_replies = oldpend->next;
@@ -168,12 +169,17 @@ static int read_packet(XCBConnection *c)
         cur->next = 0;
         *c->in.current_reply_tail = cur;
         c->in.current_reply_tail = &cur->next;
-        for(reader = c->in.readers; reader && reader->request <= c->in.request_read; reader = reader->next)
+        for(reader = c->in.readers; 
+	    reader && 
+	    XCB_SEQUENCE_COMPARE(reader->request, <=, c->in.request_read);
+	    reader = reader->next)
+	{
             if(reader->request == c->in.request_read)
             {
                 pthread_cond_signal(reader->data);
                 break;
             }
+	}
         return 1;
     }
 
@@ -249,7 +255,7 @@ static int poll_for_reply(XCBConnection *c, unsigned int request, void **reply,
         head = 0;
     /* We've read requests past the one we want, so if it has replies we have
      * them all and they're in the replies map. */
-    else if(request < c->in.request_read)
+    else if(XCB_SEQUENCE_COMPARE(request, <, c->in.request_read))
     {
         head = _xcb_map_remove(c->in.replies, request);
         if(head && head->next)
@@ -312,8 +318,13 @@ void *XCBWaitForReply(XCBConnection *c, unsigned int request, XCBGenericError **
         reader_list reader;
         reader_list **prev_reader;
 
-        for(prev_reader = &c->in.readers; *prev_reader && (*prev_reader)->request <= request; prev_reader = &(*prev_reader)->next)
+        for(prev_reader = &c->in.readers; 
+	    *prev_reader && 
+	    XCB_SEQUENCE_COMPARE ((*prev_reader)->request, <=, request);
+	    prev_reader = &(*prev_reader)->next)
+	{
             /* empty */;
+	}
         reader.request = request;
         reader.data = &cond;
         reader.next = *prev_reader;
@@ -323,12 +334,17 @@ void *XCBWaitForReply(XCBConnection *c, unsigned int request, XCBGenericError **
             if(!_xcb_conn_wait(c, &cond, 0, 0))
                 break;
 
-        for(prev_reader = &c->in.readers; *prev_reader && (*prev_reader)->request <= request; prev_reader = &(*prev_reader)->next)
+        for(prev_reader = &c->in.readers;
+	    *prev_reader && 
+	    XCB_SEQUENCE_COMPARE((*prev_reader)->request, <=, request);
+	    prev_reader = &(*prev_reader)->next)
+	{
             if(*prev_reader == &reader)
             {
                 *prev_reader = (*prev_reader)->next;
                 break;
             }
+	}
         pthread_cond_destroy(&cond);
     }
 
diff --git a/src/xcb_out.c b/src/xcb_out.c
index f12a071..9a67ad2 100644
--- a/src/xcb_out.c
+++ b/src/xcb_out.c
@@ -157,16 +157,22 @@ unsigned int XCBSendRequest(XCBConnection *c, int flags, struct iovec *vector, c
     while(c->out.writing)
         pthread_cond_wait(&c->out.cond, &c->iolock);
 
-    if(req->isvoid && c->out.request == c->in.request_expected + (1 << 16) - 2)
+    request = ++c->out.request;
+    /* send GetInputFocus (sync) when 64k-2 requests have been sent without
+     * a reply.
+     * Also send sync (could use NoOp) at 32-bit wrap to avoid having
+     * applications see sequence 0 as that is used to indicate
+     * an error in sending the request */
+    if((req->isvoid &&
+	c->out.request == c->in.request_expected + (1 << 16) - 2) ||
+       request == 0)
     {
         prefix[0] = sync.packet;
-        request = ++c->out.request;
         _xcb_in_expect_reply(c, request, WORKAROUND_NONE, XCB_REQUEST_DISCARD_REPLY);
         c->in.request_expected = c->out.request;
+	request = ++c->out.request;
     }
 
-    request = ++c->out.request;
-    assert(request != 0);
     if(workaround != WORKAROUND_NONE || flags != 0)
         _xcb_in_expect_reply(c, request, workaround, flags);
     if(!req->isvoid)
@@ -238,8 +244,8 @@ int _xcb_out_send(XCBConnection *c, struct iovec **vector, int *count)
 
 int _xcb_out_flush_to(XCBConnection *c, unsigned int request)
 {
-    assert(request <= c->out.request);
-    if(c->out.request_written >= request)
+    assert(XCB_SEQUENCE_COMPARE(request, <=, c->out.request));
+    if(XCB_SEQUENCE_COMPARE(c->out.request_written, >=, request))
         return 1;
     if(c->out.queue_len)
     {
@@ -252,6 +258,6 @@ int _xcb_out_flush_to(XCBConnection *c, unsigned int request)
     }
     while(c->out.writing)
         pthread_cond_wait(&c->out.cond, &c->iolock);
-    assert(c->out.request_written >= request);
+    assert(XCB_SEQUENCE_COMPARE(c->out.request_written, >=, request));
     return 1;
 }
diff --git a/src/xcbint.h b/src/xcbint.h
index a6d92aa..9048e9d 100644
--- a/src/xcbint.h
+++ b/src/xcbint.h
@@ -43,6 +43,8 @@ enum workarounds {
 
 #define XCB_PAD(i) (-(i) & 3)
 
+#define XCB_SEQUENCE_COMPARE(a,op,b)	((int) ((a) - (b)) op 0)
+
 /* xcb_list.c */
 
 typedef void (*XCBListFreeFunc)(void *);