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Fix hang in xcb_request_check() 

This fixes https://gitlab.freedesktop.org/xorg/lib/libxcb/-/issues/53

The issue was that libxcb expected to get a reply based on the request_expected
variable, but a reply would never arrive because the request was never actually
written.  To resolve this, a separate request_expected_written variable is
added.
This commit is contained in:
Thomas Anderson 2020-12-02 00:25:42 +00:00
parent dc28118747
commit 233d7b7f1f
3 changed files with 12 additions and 4 deletions
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13
src/xcb_in.c
View File

@ -736,11 +736,16 @@ xcb_generic_error_t *xcb_request_check(xcb_connection_t *c, xcb_void_cookie_t co
return 0; return 0;
pthread_mutex_lock(&c->iolock); pthread_mutex_lock(&c->iolock);
request = widen(c, cookie.sequence); request = widen(c, cookie.sequence);
if(XCB_SEQUENCE_COMPARE(request, >=, c->in.request_expected) if (XCB_SEQUENCE_COMPARE(request, >, c->in.request_completed))
&& XCB_SEQUENCE_COMPARE(request, >, c->in.request_completed))
{ {
_xcb_out_send_sync(c); if(XCB_SEQUENCE_COMPARE(request, >=, c->in.request_expected))
_xcb_out_flush_to(c, c->out.request); {
_xcb_out_send_sync(c);
}
if (XCB_SEQUENCE_COMPARE(request, >=, c->out.request_expected_written))
{
_xcb_out_flush_to(c, c->out.request);
}
} }
reply = wait_for_reply(c, request, &ret); reply = wait_for_reply(c, request, &ret);
assert(!reply); assert(!reply);

2
src/xcb_out.c
View File

@ -447,6 +447,7 @@ int _xcb_out_init(_xcb_out *out)
out->request = 0; out->request = 0;
out->request_written = 0; out->request_written = 0;
out->request_expected_written = 0;
if(pthread_mutex_init(&out->reqlenlock, 0)) if(pthread_mutex_init(&out->reqlenlock, 0))
return 0; return 0;
@ -467,6 +468,7 @@ int _xcb_out_send(xcb_connection_t *c, struct iovec *vector, int count)
while(ret && count) while(ret && count)
ret = _xcb_conn_wait(c, &c->out.cond, &vector, &count); ret = _xcb_conn_wait(c, &c->out.cond, &vector, &count);
c->out.request_written = c->out.request; c->out.request_written = c->out.request;
c->out.request_expected_written = c->in.request_expected;
pthread_cond_broadcast(&c->out.cond); pthread_cond_broadcast(&c->out.cond);
_xcb_in_wake_up_next_reader(c); _xcb_in_wake_up_next_reader(c);
return ret; return ret;

1
src/xcbint.h
View File

@ -113,6 +113,7 @@ typedef struct _xcb_out {
uint64_t request; uint64_t request;
uint64_t request_written; uint64_t request_written;
uint64_t request_expected_written;
uint64_t total_written; uint64_t total_written;
pthread_mutex_t reqlenlock; pthread_mutex_t reqlenlock;