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xs: fixes to watch thread creation

PATCH In review Simon Rowe 2 participants 4 messages Jun 6, 2012 – Jun 7, 2012

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Simon Rowe

author
#0 lore raw

PATCH v3 1/1 xs: fixes to watch thread creation

A pair of patches to the xenstore library that:

1) blocks signal delivery before creating the watch wakeup thread

2) reduces the stack size of the watch wakeup thread.

author
#1 lore raw

PATCH v3 1/1 xs: block signals in watch wakeup thread

The thread created to wakeup watchers is not intended to handle signals (and a later patch will reduce it's stack size which makes it unsuitable for doing so).

Signed-off-by Simon Rowe <[email protected]>
tools/xenstore/xs.c +7 -0
diff -r 6bea63e6c780 -r 711a707dc776 tools/xenstore/xs.c
@@ -705,11 +705,18 @@ bool xs_watch(struct xs_handle *h, const
 	/* We dynamically create a reader thread on demand. */
 	mutex_lock(&h->request_mutex);
 	if (!h->read_thr_exists) {
+		sigset_t set, old_set;
+
+		sigfillset(&set);
+		pthread_sigmask(SIG_SETMASK, &set, &old_set);
+
 		if (pthread_create(&h->read_thr, NULL, read_thread, h) != 0) {
+			pthread_sigmask(SIG_SETMASK, &old_set, NULL);
 			mutex_unlock(&h->request_mutex);
 			return false;
 		}
 		h->read_thr_exists = 1;
+		pthread_sigmask(SIG_SETMASK, &old_set, NULL);
 	}
 	mutex_unlock(&h->request_mutex);
 #endif
author
#2 lore raw

PATCH v3 1/1 xs: set read_thread stacksize

In reply to Simon Rowe

xs_watch() creates a thread to wake watchers using default attributes. The stacksize can be quite large (8 MB on Linux), applications that link against xenstore end up having a larger memory footprint than necessary.

Signed-off-by Simon Rowe <[email protected]>

---
Changed since v1:
* remove test for _POSIX_THREAD_ATTR_STACKSIZE
* use define for constant

tools/xenstore/xs.c +16 -1
diff -r 711a707dc776 -r ae3a05009962 tools/xenstore/xs.c
@@ -702,21 +702,36 @@ bool xs_watch(struct xs_handle *h, const
 	struct iovec iov[2];
 
 #ifdef USE_PTHREAD
+#define READ_THREAD_STACKSIZE (16 * 1024)
+
 	/* We dynamically create a reader thread on demand. */
 	mutex_lock(&h->request_mutex);
 	if (!h->read_thr_exists) {
 		sigset_t set, old_set;
+		pthread_attr_t attr;
+
+		if (pthread_attr_init(&attr) != 0) {
+			mutex_unlock(&h->request_mutex);
+			return false;
+		}
+		if (pthread_attr_setstacksize(&attr, READ_THREAD_STACKSIZE) != 0) {
+			pthread_attr_destroy(&attr);
+			mutex_unlock(&h->request_mutex);
+			return false;
+		}
 
 		sigfillset(&set);
 		pthread_sigmask(SIG_SETMASK, &set, &old_set);
 
-		if (pthread_create(&h->read_thr, NULL, read_thread, h) != 0) {
+		if (pthread_create(&h->read_thr, &attr, read_thread, h) != 0) {
 			pthread_sigmask(SIG_SETMASK, &old_set, NULL);
+			pthread_attr_destroy(&attr);
 			mutex_unlock(&h->request_mutex);
 			return false;
 		}
 		h->read_thr_exists = 1;
 		pthread_sigmask(SIG_SETMASK, &old_set, NULL);
+		pthread_attr_destroy(&attr);
 	}
 	mutex_unlock(&h->request_mutex);
 #endif