os: Implement support for NotifyFd X_NOTIFY_WRITE

This adds the ability to be notified when a file descriptor is
available for writing.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

4 files changed, 59 insertions, 24 deletions

diff --git a/os/WaitFor.c b/os/WaitFor.c
index 12b21bb21..b579e1b01 100644
--- a/os/WaitFor.c
+++ b/os/WaitFor.c
@@ -156,6 +156,7 @@ WaitForSomething(int *pClientsReady)
     fd_set devicesReadable;
     CARD32 now = 0;
     Bool someReady = FALSE;
+    Bool someNotifyWriteReady = FALSE;
 
     FD_ZERO(&clientsReadable);
     FD_ZERO(&clientsWritable);
@@ -213,9 +214,10 @@ WaitForSomething(int *pClientsReady)
         /* keep this check close to select() call to minimize race */
         if (dispatchException)
             i = -1;
-        else if (AnyClientsWriteBlocked) {
-            XFD_COPYSET(&ClientsWriteBlocked, &clientsWritable);
-            i = Select(MaxClients, &LastSelectMask, &clientsWritable, NULL, wt);
+        else if (AnyWritesPending) {
+            XFD_COPYSET(&ClientsWriteBlocked, &LastSelectWriteMask);
+            XFD_ORSET(&LastSelectWriteMask, &NotifyWriteFds, &LastSelectWriteMask);
+            i = Select(MaxClients, &LastSelectMask, &LastSelectWriteMask, NULL, wt);
         }
         else {
             i = Select(MaxClients, &LastSelectMask, NULL, NULL, wt);
@@ -291,12 +293,20 @@ WaitForSomething(int *pClientsReady)
             }
             if (someReady)
                 XFD_ORSET(&LastSelectMask, &ClientsWithInput, &LastSelectMask);
-            if (AnyClientsWriteBlocked && XFD_ANYSET(&clientsWritable)) {
-                NewOutputPending = TRUE;
-                XFD_ORSET(&OutputPending, &clientsWritable, &OutputPending);
-                XFD_UNSET(&ClientsWriteBlocked, &clientsWritable);
-                if (!XFD_ANYSET(&ClientsWriteBlocked))
-                    AnyClientsWriteBlocked = FALSE;
+            if (AnyWritesPending) {
+                XFD_ANDSET(&clientsWritable, &LastSelectWriteMask, &ClientsWriteBlocked);
+                if (XFD_ANYSET(&clientsWritable)) {
+                    NewOutputPending = TRUE;
+                    XFD_ORSET(&OutputPending, &clientsWritable, &OutputPending);
+                    XFD_UNSET(&ClientsWriteBlocked, &clientsWritable);
+                    if (!XFD_ANYSET(&ClientsWriteBlocked) && NumNotifyWriteFd == 0)
+                        AnyWritesPending = FALSE;
+                }
+                if (NumNotifyWriteFd != 0) {
+                    XFD_ANDSET(&tmp_set, &LastSelectWriteMask, &NotifyWriteFds);
+                    if (XFD_ANYSET(&tmp_set))
+                        someNotifyWriteReady = TRUE;
+                }
             }
 
             XFD_ANDSET(&devicesReadable, &LastSelectMask, &EnabledDevices);
@@ -307,7 +317,7 @@ WaitForSomething(int *pClientsReady)
                               (void *) &LastSelectMask);
 
             XFD_ANDSET(&tmp_set, &LastSelectMask, &NotifyReadFds);
-            if (XFD_ANYSET(&tmp_set))
+            if (XFD_ANYSET(&tmp_set) || someNotifyWriteReady)
                 HandleNotifyFds();
 
             if (XFD_ANYSET(&devicesReadable) || XFD_ANYSET(&clientsReadable))
diff --git a/os/connection.c b/os/connection.c
index 0df439189..4da01a641 100644
--- a/os/connection.c
+++ b/os/connection.c
@@ -124,15 +124,18 @@ static int lastfdesc;           /* maximum file descriptor */
 fd_set WellKnownConnections;    /* Listener mask */
 fd_set EnabledDevices;          /* mask for input devices that are on */
 fd_set NotifyReadFds;           /* mask for other file descriptors */
+fd_set NotifyWriteFds;          /* mask for other write file descriptors */
 fd_set AllSockets;              /* select on this */
 fd_set AllClients;              /* available clients */
 fd_set LastSelectMask;          /* mask returned from last select call */
+fd_set LastSelectWriteMask;     /* mask returned from last select call */
 fd_set ClientsWithInput;        /* clients with FULL requests in buffer */
 fd_set ClientsWriteBlocked;     /* clients who cannot receive output */
 fd_set OutputPending;           /* clients with reply/event data ready to go */
 int MaxClients = 0;
+int NumNotifyWriteFd;           /* Number of NotifyFd members with write set */
 Bool NewOutputPending;          /* not yet attempted to write some new output */
-Bool AnyClientsWriteBlocked;    /* true if some client blocked on write */
+Bool AnyWritesPending;          /* true if some client blocked on write or NotifyFd with write */
 Bool NoListenAll;               /* Don't establish any listening sockets */
 
 static Bool RunFromSmartParent; /* send SIGUSR1 to parent process */
@@ -969,8 +972,8 @@ CloseDownFileDescriptor(OsCommPtr oc)
         FD_CLR(connection, &SavedClientsWithInput);
     }
     FD_CLR(connection, &ClientsWriteBlocked);
-    if (!XFD_ANYSET(&ClientsWriteBlocked))
-        AnyClientsWriteBlocked = FALSE;
+    if (!XFD_ANYSET(&ClientsWriteBlocked) && NumNotifyWriteFd == 0)
+        AnyWritesPending = FALSE;
     FD_CLR(connection, &OutputPending);
 }
 
@@ -1112,6 +1115,7 @@ InitNotifyFds(void)
             RemoveNotifyFd(s->fd);
 
     xorg_list_init(&notify_fds);
+    NumNotifyWriteFd = 0;
     been_here = 1;
 }
 
@@ -1153,6 +1157,20 @@ SetNotifyFd(int fd, NotifyFdProcPtr notify, int mask, void *data)
             FD_CLR(fd, &NotifyReadFds);
         }
     }
+
+    if (changes & X_NOTIFY_WRITE) {
+        if (mask & X_NOTIFY_WRITE) {
+            FD_SET(fd, &NotifyWriteFds);
+            if (!NumNotifyWriteFd++)
+                AnyWritesPending = TRUE;
+        } else {
+            FD_CLR(fd, &NotifyWriteFds);
+            if (!--NumNotifyWriteFd)
+                if (!XFD_ANYSET(&ClientsWriteBlocked))
+                    AnyWritesPending = FALSE;
+        }
+    }
+
     if (mask == 0) {
         xorg_list_del(&n->list);
         free(n);
@@ -1174,12 +1192,16 @@ SetNotifyFd(int fd, NotifyFdProcPtr notify, int mask, void *data)
 void
 HandleNotifyFds(void)
 {
-    struct notify_fd *s, *next;
-
-    xorg_list_for_each_entry_safe(s, next, &notify_fds, list) {
-        if (FD_ISSET(s->fd, &LastSelectMask)) {
-            s->notify(s->fd, X_NOTIFY_READ, s->data);
-        }
+    struct notify_fd *n, *next;
+
+    xorg_list_for_each_entry_safe(n, next, &notify_fds, list) {
+        int ready = 0;
+        if ((n->mask & X_NOTIFY_READ) && FD_ISSET(n->fd, &LastSelectMask))
+            ready |= X_NOTIFY_READ;
+        if ((n->mask & X_NOTIFY_WRITE) & FD_ISSET(n->fd, &LastSelectWriteMask))
+            ready |= X_NOTIFY_WRITE;
+        if (ready != 0)
+            n->notify(n->fd, ready, n->data);
     }
 }
 
diff --git a/os/io.c b/os/io.c
index 971fdc951..19a449ad8 100644
--- a/os/io.c
+++ b/os/io.c
@@ -946,7 +946,7 @@ FlushClient(ClientPtr who, OsCommPtr oc, const void *__extraBuf, int extraCount)
                and not ready to accept more.  Make a note of it and buffer
                the rest. */
             FD_SET(connection, &ClientsWriteBlocked);
-            AnyClientsWriteBlocked = TRUE;
+            AnyWritesPending = TRUE;
 
             if (written < oco->count) {
                 if (written > 0) {
@@ -1009,10 +1009,10 @@ FlushClient(ClientPtr who, OsCommPtr oc, const void *__extraBuf, int extraCount)
     /* everything was flushed out */
     oco->count = 0;
     /* check to see if this client was write blocked */
-    if (AnyClientsWriteBlocked) {
+    if (AnyWritesPending) {
         FD_CLR(oc->fd, &ClientsWriteBlocked);
-        if (!XFD_ANYSET(&ClientsWriteBlocked))
-            AnyClientsWriteBlocked = FALSE;
+        if (!XFD_ANYSET(&ClientsWriteBlocked) && NumNotifyWriteFd == 0)
+            AnyWritesPending = FALSE;
     }
     if (oco->size > BUFWATERMARK) {
         free(oco->buf);
diff --git a/os/osdep.h b/os/osdep.h
index 2bfc783f0..2fbfc48f6 100644
--- a/os/osdep.h
+++ b/os/osdep.h
@@ -168,9 +168,11 @@ extern void HandleNotifyFds(void);
 extern fd_set AllSockets;
 extern fd_set AllClients;
 extern fd_set LastSelectMask;
+extern fd_set LastSelectWriteMask;
 extern fd_set WellKnownConnections;
 extern fd_set EnabledDevices;
 extern fd_set NotifyReadFds;
+extern fd_set NotifyWriteFds;
 extern fd_set ClientsWithInput;
 extern fd_set ClientsWriteBlocked;
 extern fd_set OutputPending;
@@ -185,7 +187,8 @@ extern void ClearConnectionTranslation(void);
 #endif
 
 extern Bool NewOutputPending;
-extern Bool AnyClientsWriteBlocked;
+extern Bool AnyWritesPending;
+extern Bool NumNotifyWriteFd;
 
 extern WorkQueuePtr workQueue;