Keith Packard escreveu:
The input thread will block before enqueuing while the X server pulls
events out of the queue, causing it to stop reading events and updating
the cursor.
Indeed.
The following patch assert the order of events enqueued with a mutex
protecting writes to the tail pointer in mieqEnqueue. If the main thread
blocks somehow, the input thread continues doing its job. All
mieqEnqueue users must be safe now.
The X server also reads the input queue pointers from DIX before calling
into ProcessInputEvents, so you aren't safe against memory write races
(where writes to one location are visible across CPUs before writes to
another location).
I think this can be easily changed by nonblocking pipes. If someone
wants to wakeup PIE, then just write on the pipe in which this function
is listening. I have to think a little more about this but it may be
easy to address.
So, we either need to fix the users of checkForInput along with all
users of miEventQueue, or we need to assert that we're running on a
sensible CPU that doesn't require a mutex to make memory changes visible
across processors, in which case we don't need any mutex at all.
I really don't know how to check if a CPU is visible to the other CPU.
Thanks,
--
Tiago Vignatti
C3SL - Centro de Computação Científica e Software Livre
www.c3sl.ufpr.br
diff --git a/mi/mieq.c b/mi/mieq.c
index 0a1b740..d96c545 100644
--- a/mi/mieq.c
+++ b/mi/mieq.c
@@ -53,6 +53,10 @@ in this Software without prior written authorization from The Open Group.
# include "extinit.h"
# include "exglobals.h"
+#ifdef INPUT_THREAD
+#include <pthread.h>
+#endif
+
#ifdef DPMSExtension
# include "dpmsproc.h"
# define DPMS_SERVER
@@ -81,6 +85,10 @@ typedef struct _EventQueue {
static EventQueueRec miEventQueue;
+#ifdef INPUT_THREAD
+pthread_mutex_t miTailQueueMutex = PTHREAD_MUTEX_INITIALIZER;
+#endif
+
Bool
mieqInit(void)
{
@@ -122,6 +130,9 @@ mieqResizeEvents(int min_size)
void
mieqEnqueue(DeviceIntPtr pDev, xEvent *e)
{
+#ifdef INPUT_THREAD
+ pthread_mutex_lock(&miTailQueueMutex);
+#endif
unsigned int oldtail = miEventQueue.tail, newtail;
EventListPtr evt;
int isMotion = 0;
@@ -146,6 +157,9 @@ mieqEnqueue(DeviceIntPtr pDev, xEvent *e)
if (laste->nevents > 6) {
ErrorF("[mi] mieqEnqueue: more than six valuator events; dropping.\n");
+#ifdef INPUT_THREAD
+ pthread_mutex_unlock(&miTailQueueMutex);
+#endif
return;
}
if (oldtail == miEventQueue.head ||
@@ -157,10 +171,16 @@ mieqEnqueue(DeviceIntPtr pDev, xEvent *e)
((lastkbp->deviceid & DEVICE_BITS) !=
(v->deviceid & DEVICE_BITS))) {
ErrorF("[mi] mieqEnequeue: out-of-order valuator event; dropping.\n");
+#ifdef INPUT_THREAD
+ pthread_mutex_unlock(&miTailQueueMutex);
+#endif
return;
}
memcpy((laste->events[laste->nevents++].event), e, sizeof(xEvent));
+#ifdef INPUT_THREAD
+ pthread_mutex_unlock(&miTailQueueMutex);
+#endif
return;
}
@@ -176,6 +196,9 @@ mieqEnqueue(DeviceIntPtr pDev, xEvent *e)
if (newtail == miEventQueue.head) {
ErrorF("[mi] EQ overflowing. The server is probably stuck "
"in an infinite loop.\n");
+#ifdef INPUT_THREAD
+ pthread_mutex_unlock(&miTailQueueMutex);
+#endif
return;
}
miEventQueue.tail = newtail;
@@ -193,6 +216,9 @@ mieqEnqueue(DeviceIntPtr pDev, xEvent *e)
if (!evt->event)
{
ErrorF("[mi] Running out of memory. Tossing event.\n");
+#ifdef INPUT_THREAD
+ pthread_mutex_unlock(&miTailQueueMutex);
+#endif
return;
}
}
@@ -212,6 +238,9 @@ mieqEnqueue(DeviceIntPtr pDev, xEvent *e)
miEventQueue.events[oldtail].pDev = pDev;
miEventQueue.lastMotion = isMotion;
+#ifdef INPUT_THREAD
+ pthread_mutex_unlock(&miTailQueueMutex);
+#endif
}
void
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