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authorRich Felker <dalias@aerifal.cx>2018-05-09 00:14:13 -0400
committerRich Felker <dalias@aerifal.cx>2018-05-09 00:36:09 -0400
commitb8742f32602add243ee2ce74d804015463726899 (patch)
tree5a511e7d917a38bab0c2bb3aaa7457e6dd85e797 /src/thread/pthread_create.c
parent1db9a35569d51155eb7f2ccf26d420ae4e42e416 (diff)
downloadmusl-b8742f32602add243ee2ce74d804015463726899.tar.gz
improve design of thread-start with explicit scheduling attributes
eliminate the awkward startlock mechanism and corresponding fields of the pthread structure that were only used at startup. instead of having pthread_create perform the scheduling operations and having the new thread wait for them to be completed, start the new thread with a wrapper start function that performs its own scheduling, sending the result code back via a futex. this way the new thread can use storage from the calling thread's stack rather than permanent fields in the pthread structure.
Diffstat (limited to 'src/thread/pthread_create.c')
-rw-r--r--src/thread/pthread_create.c60
1 files changed, 39 insertions, 21 deletions
diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index e07d29e3..5f07ab49 100644
--- a/src/thread/pthread_create.c
+++ b/src/thread/pthread_create.c
@@ -132,22 +132,36 @@ void __do_cleanup_pop(struct __ptcb *cb)
__pthread_self()->cancelbuf = cb->__next;
}
+struct start_sched_args {
+ void *start_arg;
+ void *(*start_fn)(void *);
+ sigset_t mask;
+ pthread_attr_t *attr;
+ volatile int futex;
+};
+
+static void *start_sched(void *p)
+{
+ struct start_sched_args *ssa = p;
+ void *start_arg = ssa->start_arg;
+ void *(*start_fn)(void *) = ssa->start_fn;
+ pthread_t self = __pthread_self();
+
+ int ret = -__syscall(SYS_sched_setscheduler, self->tid,
+ ssa->attr->_a_policy, &ssa->attr->_a_prio);
+ if (!ret) __restore_sigs(&ssa->mask);
+ a_store(&ssa->futex, ret);
+ __wake(&ssa->futex, 1, 1);
+ if (ret) {
+ self->detach_state = DT_DYNAMIC;
+ return 0;
+ }
+ return start_fn(start_arg);
+}
+
static int start(void *p)
{
pthread_t self = p;
- /* States for startlock:
- * 0 = no need for start sync
- * 1 = waiting for parent to do work
- * 2 = failure in parent, child must abort
- * 3 = success in parent, child must restore sigmask */
- if (self->startlock[0]) {
- __wait(self->startlock, 0, 1, 1);
- if (self->startlock[0] == 2) {
- self->detach_state = DT_DYNAMIC;
- pthread_exit(0);
- }
- __restore_sigs(self->sigmask);
- }
if (self->unblock_cancel)
__syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
SIGPT_SET, 0, _NSIG/8);
@@ -198,6 +212,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
| CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID | CLONE_DETACHED;
int do_sched = 0;
pthread_attr_t attr = { 0 };
+ struct start_sched_args ssa;
if (!libc.can_do_threads) return ENOSYS;
self = __pthread_self();
@@ -282,8 +297,14 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
new->detach_state = DT_JOINABLE;
}
if (attr._a_sched) {
- do_sched = new->startlock[0] = 1;
- __block_app_sigs(new->sigmask);
+ do_sched = 1;
+ ssa.futex = -1;
+ ssa.start_fn = new->start;
+ ssa.start_arg = new->start_arg;
+ ssa.attr = &attr;
+ new->start = start_sched;
+ new->start_arg = &ssa;
+ __block_app_sigs(&ssa.mask);
}
new->robust_list.head = &new->robust_list.head;
new->unblock_cancel = self->cancel;
@@ -295,7 +316,7 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
__release_ptc();
if (do_sched) {
- __restore_sigs(new->sigmask);
+ __restore_sigs(&ssa.mask);
}
if (ret < 0) {
@@ -305,11 +326,8 @@ int __pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict att
}
if (do_sched) {
- ret = __syscall(SYS_sched_setscheduler, new->tid,
- attr._a_policy, &attr._a_prio);
- a_store(new->startlock, ret<0 ? 2 : 3);
- __wake(new->startlock, 1, 1);
- if (ret < 0) return -ret;
+ __futexwait(&ssa.futex, -1, 1);
+ if (ret) return ret;
}
*res = new;