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improve design of thread-start with explicit scheduling attributes

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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.
This commit is contained in:
Rich Felker 2018-05-09 00:14:13 -04:00
parent 1db9a35569
commit b8742f3260
2 changed files with 39 additions and 23 deletions
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2
src/internal/pthread_impl.h
View File

@ -47,8 +47,6 @@ struct pthread {
volatile int timer_id;
locale_t locale;
volatile int killlock[1];
volatile int startlock[1];
unsigned long sigmask[_NSIG/8/sizeof(long)];
char *dlerror_buf;
void *stdio_locks;

60
src/thread/pthread_create.c
View File

@ -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;