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.

diff --git a/src/internal/pthread_impl.h b/src/internal/pthread_impl.h
index fc2def63484922c9feadaca8b46b530c7195b293..69352ef24c22948863406c18ec11d06ffee3cbf2 100644 (file)
--- a/src/internal/pthread_impl.h
+++ b/src/internal/pthread_impl.h
@@ -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;
 

diff --git a/src/thread/pthread_create.c b/src/thread/pthread_create.c
index e07d29e30a41238d3ec4342256d7aaf977196e5e..5f07ab49ed2ea98fc04f4a9aefebf98425191427 100644 (file)
--- 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;