Don't futex_wait spin when setting properties. Wait for socket close.
Depends on init change I8dd685ea
Bug: 4185486
Change-Id: I5a2dbc3b7be1759212d4a3988d9033b9b947a1db
diff --git a/libc/bionic/system_properties.c b/libc/bionic/system_properties.c
index c40950f..3bdc9bf 100644
--- a/libc/bionic/system_properties.c
+++ b/libc/bionic/system_properties.c
@@ -30,6 +30,7 @@
#include <unistd.h>
#include <stddef.h>
#include <errno.h>
+#include <poll.h>
#include <sys/mman.h>
@@ -156,15 +157,17 @@
static int send_prop_msg(prop_msg *msg)
{
+ struct pollfd pollfds[1];
struct sockaddr_un addr;
socklen_t alen;
size_t namelen;
int s;
int r;
+ int result = -1;
s = socket(AF_LOCAL, SOCK_STREAM, 0);
if(s < 0) {
- return -1;
+ return result;
}
memset(&addr, 0, sizeof(addr));
@@ -175,30 +178,37 @@
if(TEMP_FAILURE_RETRY(connect(s, (struct sockaddr *) &addr, alen) < 0)) {
close(s);
- return -1;
+ return result;
}
r = TEMP_FAILURE_RETRY(send(s, msg, sizeof(prop_msg), 0));
if(r == sizeof(prop_msg)) {
- r = 0;
- } else {
- r = -1;
+ // We successfully wrote to the property server but now we
+ // wait for the property server to finish its work. It
+ // acknowledges its completion by closing the socket so we
+ // poll here (on nothing), waiting for the socket to close.
+ // If you 'adb shell setprop foo bar' you'll see the POLLHUP
+ // once the socket closes. Out of paranoia we cap our poll
+ // at 250 ms.
+ pollfds[0].fd = s;
+ pollfds[0].events = 0;
+ r = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
+ if (r == 1 && (pollfds[0].revents & POLLHUP) != 0) {
+ result = 0;
+ }
}
close(s);
- return r;
+ return result;
}
int __system_property_set(const char *key, const char *value)
{
- unsigned old_serial;
- volatile unsigned *serial;
- prop_msg msg;
int err;
- prop_area *pa = __system_property_area__;
int tries = 0;
int update_seen = 0;
+ prop_msg msg;
if(key == 0) return -1;
if(value == 0) value = "";
@@ -210,54 +220,11 @@
strlcpy(msg.name, key, sizeof msg.name);
strlcpy(msg.value, value, sizeof msg.value);
- /* Note the system properties serial number before we do our update. */
- const prop_info *pi = __system_property_find(key);
- if(pi != NULL) {
- serial = &pi->serial;
- } else {
- serial = &pa->serial;
- }
- old_serial = *serial;
-
err = send_prop_msg(&msg);
if(err < 0) {
return err;
}
- /**
- * Wait for the shared memory page to be written back and be
- * visible in our address space before returning to the caller
- * who might reasonably expect subsequent reads to match what was
- * just written.
- *
- * Sleep 5 ms after failed checks and only wait up to a 500 ms
- * total, just in case the system property server fails to update
- * for whatever reason.
- */
- do {
- struct timespec timeout;
- timeout.tv_sec = 0;
- timeout.tv_nsec = 2500000; // 2.5 ms
-
- if(tries++ > 0) {
- usleep(2500); // 2.5 ms
- }
- __futex_wait(serial, old_serial, &timeout);
- if(pi != NULL) {
- unsigned new_serial = *serial;
- /* Waiting on a specific prop_info to be updated. */
- if (old_serial != new_serial && !SERIAL_DIRTY(new_serial)) {
- update_seen = 1;
- }
- } else {
- /* Waiting for a prop_info to be created. */
- const prop_info *new_pi = __system_property_find(key);
- if(new_pi != NULL && !SERIAL_DIRTY(new_pi->serial)) {
- update_seen = 1;
- }
- }
- } while (!update_seen && tries < 100);
-
return 0;
}