Implement pthread_attr_getinheritsched/pthread_attr_setinheritsched.
Historically, Android defaulted to EXPLICIT but with a special case
because SCHED_NORMAL/priority 0 was awkward. Because the code couldn't
actually tell whether SCHED_NORMAL/priority 0 was a genuine attempt to
explicitly set those attributes (because the parent thread is SCHED_FIFO,
say) or just because the pthread_attr_t was left at its defaults.
Now we support INHERIT, we could call sched_getscheduler to see whether
we actually need to call sched_setscheduler, but since the major cost
is the fixed syscall overhead, we may as well just conservatively
call sched_setscheduler and let the kernel decide whether it's a
no-op. (Especially because we'd then have to add both sched_getscheduler
and sched_setscheduler to any seccomp filter.)
Platform code (or app code that only needs to support >= P) can actually
add a call to pthread_attr_setinheritsched to say that they just want
to inherit (if they know that none of their threads actually mess with
scheduler attributes at all), which will save them a sched_setscheduler
call except in the doubly-special case of SCHED_RESET_ON_FORK (which we
do handle).
An alternative would be "make pthread_attr_setschedparams and
pthread_attr_setschedprio set EXPLICIT and change the platform default
to INHERIT", but even though I can only think of weird pathological
examples where anyone would notice that change, that behavior -- of
pthread_attr_setschedparams/pthread_attr_setschedprio overriding an
earlier call to pthread_attr_setinheritsched -- isn't allowed by POSIX
(whereas defaulting to EXPLICIT is).
If we have a lot of trouble with this change in the app compatibility
testing phase, though, we'll want to reconsider this decision!
-*-
This change also removes a comment about setting the scheduler attributes
in main_thread because we'd have to actually keep them up to date,
and it's not clear that doing so would be worth the trouble.
Also make async_safe_format_log preserve errno so we don't have to be
so careful around it.
Bug: http://b/67471710
Test: ran tests
Change-Id: Idd026c4ce78a536656adcb57aa2e7b2c616eeddf
diff --git a/libc/bionic/pthread_attr.cpp b/libc/bionic/pthread_attr.cpp
index fc9e74a..0d79374 100644
--- a/libc/bionic/pthread_attr.cpp
+++ b/libc/bionic/pthread_attr.cpp
@@ -54,6 +54,23 @@
return 0;
}
+int pthread_attr_setinheritsched(pthread_attr_t* attr, int flag) {
+ if (flag == PTHREAD_EXPLICIT_SCHED) {
+ attr->flags &= ~PTHREAD_ATTR_FLAG_INHERIT;
+ } else if (flag == PTHREAD_INHERIT_SCHED) {
+ attr->flags |= PTHREAD_ATTR_FLAG_INHERIT;
+ } else {
+ return EINVAL;
+ }
+ return 0;
+}
+
+int pthread_attr_getinheritsched(const pthread_attr_t* attr, int* flag) {
+ *flag = (attr->flags & PTHREAD_ATTR_FLAG_INHERIT) ? PTHREAD_INHERIT_SCHED
+ : PTHREAD_EXPLICIT_SCHED;
+ return 0;
+}
+
int pthread_attr_setdetachstate(pthread_attr_t* attr, int state) {
if (state == PTHREAD_CREATE_DETACHED) {
attr->flags |= PTHREAD_ATTR_FLAG_DETACHED;