[musl] / src / thread / pthread_create.c

#include "pthread_impl.h"
#include "stdio_impl.h"
#include <sys/mman.h>

static void dummy_0()
{
}
weak_alias(dummy_0, __acquire_ptc);
weak_alias(dummy_0, __release_ptc);
weak_alias(dummy_0, __pthread_tsd_run_dtors);

_Noreturn void pthread_exit(void *result)
{
        pthread_t self = pthread_self();
        sigset_t set;

        self->result = result;

        while (self->cancelbuf) {
                void (*f)(void *) = self->cancelbuf->__f;
                void *x = self->cancelbuf->__x;
                self->cancelbuf = self->cancelbuf->__next;
                f(x);
        }

        __pthread_tsd_run_dtors();

        __lock(self->exitlock);

        /* Mark this thread dead before decrementing count */
        __lock(self->killlock);
        self->dead = 1;
        __unlock(self->killlock);

        /* Block all signals before decrementing the live thread count.
         * This is important to ensure that dynamically allocated TLS
         * is not under-allocated/over-committed, and possibly for other
         * reasons as well. */
        __syscall(SYS_rt_sigprocmask, SIG_BLOCK, SIGALL_SET, &set, _NSIG/8);

        /* It's impossible to determine whether this is "the last thread"
         * until performing the atomic decrement, since multiple threads
         * could exit at the same time. For the last thread, revert the
         * decrement and unblock signals to give the atexit handlers and
         * stdio cleanup code a consistent state. */
        if (a_fetch_add(&libc.threads_minus_1, -1)==0) {
                libc.threads_minus_1 = 0;
                __syscall(SYS_rt_sigprocmask, SIG_SETMASK, &set, 0, _NSIG/8);
                exit(0);
        }

        if (self->detached && self->map_base) {
                /* Detached threads must avoid the kernel clear_child_tid
                 * feature, since the virtual address will have been
                 * unmapped and possibly already reused by a new mapping
                 * at the time the kernel would perform the write. In
                 * the case of threads that started out detached, the
                 * initial clone flags are correct, but if the thread was
                 * detached later (== 2), we need to clear it here. */
                if (self->detached == 2) __syscall(SYS_set_tid_address, 0);

                /* The following call unmaps the thread's stack mapping
                 * and then exits without touching the stack. */
                __unmapself(self->map_base, self->map_size);
        }

        for (;;) __syscall(SYS_exit, 0);
}

void __do_cleanup_push(struct __ptcb *cb)
{
        struct pthread *self = pthread_self();
        cb->__next = self->cancelbuf;
        self->cancelbuf = cb;
}

void __do_cleanup_pop(struct __ptcb *cb)
{
        __pthread_self()->cancelbuf = cb->__next;
}

static int start(void *p)
{
        pthread_t self = p;
        if (self->startlock[0]) {
                __wait(self->startlock, 0, 1, 1);
                if (self->startlock[0]) {
                        self->detached = 2;
                        pthread_exit(0);
                }
                __syscall(SYS_rt_sigprocmask, SIG_SETMASK,
                        self->sigmask, 0, _NSIG/8);
        }
        if (self->unblock_cancel)
                __syscall(SYS_rt_sigprocmask, SIG_UNBLOCK,
                        SIGPT_SET, 0, _NSIG/8);
        pthread_exit(self->start(self->start_arg));
        return 0;
}

#define ROUND(x) (((x)+PAGE_SIZE-1)&-PAGE_SIZE)

/* pthread_key_create.c overrides this */
static const size_t dummy = 0;
weak_alias(dummy, __pthread_tsd_size);

static FILE *const dummy_file = 0;
weak_alias(dummy_file, __stdin_used);
weak_alias(dummy_file, __stdout_used);
weak_alias(dummy_file, __stderr_used);

static void init_file_lock(FILE *f)
{
        if (f && f->lock<0) f->lock = 0;
}

void *__copy_tls(unsigned char *);

int pthread_create(pthread_t *restrict res, const pthread_attr_t *restrict attrp, void *(*entry)(void *), void *restrict arg)
{
        int ret;
        size_t size, guard;
        struct pthread *self = pthread_self(), *new;
        unsigned char *map = 0, *stack = 0, *tsd = 0, *stack_limit;
        unsigned flags = 0x7d8f00;
        int do_sched = 0;
        pthread_attr_t attr = {0};

        if (!self) return ENOSYS;
        if (!libc.threaded) {
                for (FILE *f=libc.ofl_head; f; f=f->next)
                        init_file_lock(f);
                init_file_lock(__stdin_used);
                init_file_lock(__stdout_used);
                init_file_lock(__stderr_used);
                libc.threaded = 1;
        }
        if (attrp) attr = *attrp;

        __acquire_ptc();

        if (attr._a_stackaddr) {
                size_t need = libc.tls_size + __pthread_tsd_size;
                size = attr._a_stacksize + DEFAULT_STACK_SIZE;
                stack = (void *)(attr._a_stackaddr & -16);
                stack_limit = (void *)(attr._a_stackaddr - size);
                /* Use application-provided stack for TLS only when
                 * it does not take more than ~12% or 2k of the
                 * application's stack space. */
                if (need < size/8 && need < 2048) {
                        tsd = stack - __pthread_tsd_size;
                        stack = tsd - libc.tls_size;
                } else {
                        size = ROUND(need);
                        guard = 0;
                }
        } else {
                guard = ROUND(DEFAULT_GUARD_SIZE + attr._a_guardsize);
                size = guard + ROUND(DEFAULT_STACK_SIZE + attr._a_stacksize
                        + libc.tls_size +  __pthread_tsd_size);
        }

        if (!tsd) {
                if (guard) {
                        map = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANON, -1, 0);
                        if (map == MAP_FAILED) goto fail;
                        if (mprotect(map+guard, size-guard, PROT_READ|PROT_WRITE)) {
                                munmap(map, size);
                                goto fail;
                        }
                } else {
                        map = mmap(0, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 0);
                        if (map == MAP_FAILED) goto fail;
                }
                tsd = map + size - __pthread_tsd_size;
                if (!stack) {
                        stack = tsd - libc.tls_size;
                        stack_limit = map + guard;
                }
        }

        new = __copy_tls(tsd - libc.tls_size);
        new->map_base = map;
        new->map_size = size;
        new->stack = stack;
        new->stack_size = stack - stack_limit;
        new->pid = self->pid;
        new->errno_ptr = &new->errno_val;
        new->start = entry;
        new->start_arg = arg;
        new->self = new;
        new->tsd = (void *)tsd;
        if (attr._a_detach) {
                new->detached = 1;
                flags -= 0x200000;
        }
        if (attr._a_sched) {
                do_sched = new->startlock[0] = 1;
                __syscall(SYS_rt_sigprocmask, SIG_BLOCK,
                        SIGALL_SET, new->sigmask, _NSIG/8);
        }
        new->unblock_cancel = self->cancel;
        new->canary = self->canary;

        a_inc(&libc.threads_minus_1);
        ret = __clone(start, stack, flags, new, &new->tid, TP_ADJ(new), &new->tid);

        __release_ptc();

        if (do_sched) {
                __syscall(SYS_rt_sigprocmask, SIG_SETMASK,
                        new->sigmask, 0, _NSIG/8);
        }

        if (ret < 0) {
                a_dec(&libc.threads_minus_1);
                if (map) munmap(map, size);
                return EAGAIN;
        }

        if (do_sched) {
                ret = __syscall(SYS_sched_setscheduler, new->tid,
                        attr._a_policy, &attr._a_prio);
                a_store(new->startlock, ret<0 ? 2 : 0);
                __wake(new->startlock, 1, 1);
                if (ret < 0) return -ret;
        }

        *res = new;
        return 0;
fail:
        __release_ptc();
        return EAGAIN;
}