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Get rid of kmalloc()

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This changes *NSYNC to allocate waiters on the stack so our locks don't
need to depend on dynamic memory. This make our runtiem simpler, and it
also fixes bugs with thread cancellation support.
This commit is contained in:
Justine Tunney 2023-09-11 21:34:53 -07:00
parent 77a7873057
commit a359de7893
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GPG key ID: BE714B4575D6E328
57 changed files with 405 additions and 472 deletions
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91
third_party/nsync/common.c vendored
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@ -16,10 +16,6 @@
│ limitations under the License. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/intrin/dll.h"
#include "libc/intrin/kmalloc.h"
#include "libc/mem/mem.h"
#include "libc/runtime/runtime.h"
#include "libc/thread/thread.h"
#include "libc/thread/tls.h"
#include "third_party/nsync/atomic.h"
#include "third_party/nsync/atomic.internal.h"
@ -147,78 +143,25 @@ waiter *nsync_dll_waiter_samecond_ (struct Dll *e) {
/* -------------------------------- */
static struct Dll *free_waiters = NULL;
/* free_waiters points to a doubly-linked list of free waiter structs. */
static nsync_atomic_uint32_ free_waiters_mu; /* spinlock; protects free_waiters */
#define waiter_for_thread __get_tls()->tib_nsync
static void waiter_destroy (void *v) {
waiter *w = (waiter *) v;
/* Reset waiter_for_thread in case another thread-local variable reuses
the waiter in its destructor while the waiter is taken by the other
thread from free_waiters. This can happen as the destruction order
of thread-local variables can be arbitrary in some platform e.g.
POSIX. */
waiter_for_thread = NULL;
IGNORE_RACES_START ();
ASSERT ((w->flags & (WAITER_RESERVED|WAITER_IN_USE)) == WAITER_RESERVED);
w->flags &= ~WAITER_RESERVED;
nsync_spin_test_and_set_ (&free_waiters_mu, 1, 1, 0);
dll_make_first (&free_waiters, &w->nw.q);
ATM_STORE_REL (&free_waiters_mu, 0); /* release store */
IGNORE_RACES_END ();
/* Initializes waiter struct. */
void nsync_waiter_init_ (waiter *w) {
w->tag = WAITER_TAG;
w->nw.tag = NSYNC_WAITER_TAG;
nsync_mu_semaphore_init (&w->sem);
w->nw.sem = &w->sem;
dll_init (&w->nw.q);
NSYNC_ATOMIC_UINT32_STORE_ (&w->nw.waiting, 0);
w->nw.flags = NSYNC_WAITER_FLAG_MUCV;
ATM_STORE (&w->remove_count, 0);
dll_init (&w->same_condition);
w->flags = WAITER_IN_USE;
}
/* Return a pointer to an unused waiter struct.
Ensures that the enclosed timer is stopped and its channel drained. */
waiter *nsync_waiter_new_ (void) {
struct Dll *q;
waiter *tw;
waiter *w;
tw = waiter_for_thread;
w = tw;
if (w == NULL || (w->flags & (WAITER_RESERVED|WAITER_IN_USE)) != WAITER_RESERVED) {
w = NULL;
nsync_spin_test_and_set_ (&free_waiters_mu, 1, 1, 0);
q = dll_first (free_waiters);
if (q != NULL) { /* If free list is non-empty, dequeue an item. */
dll_remove (&free_waiters, q);
w = DLL_WAITER (q);
}
ATM_STORE_REL (&free_waiters_mu, 0); /* release store */
if (w == NULL) { /* If free list was empty, allocate an item. */
w = (waiter *) kmalloc (sizeof (*w));
w->tag = WAITER_TAG;
w->nw.tag = NSYNC_WAITER_TAG;
nsync_mu_semaphore_init (&w->sem);
w->nw.sem = &w->sem;
dll_init (&w->nw.q);
NSYNC_ATOMIC_UINT32_STORE_ (&w->nw.waiting, 0);
w->nw.flags = NSYNC_WAITER_FLAG_MUCV;
ATM_STORE (&w->remove_count, 0);
dll_init (&w->same_condition);
w->flags = 0;
}
if (tw == NULL) {
w->flags |= WAITER_RESERVED;
nsync_set_per_thread_waiter_ (w, &waiter_destroy);
waiter_for_thread = w;
}
}
w->flags |= WAITER_IN_USE;
return (w);
}
/* Return an unused waiter struct *w to the free pool. */
void nsync_waiter_free_ (waiter *w) {
ASSERT ((w->flags & WAITER_IN_USE) != 0);
w->flags &= ~WAITER_IN_USE;
if ((w->flags & WAITER_RESERVED) == 0) {
nsync_spin_test_and_set_ (&free_waiters_mu, 1, 1, 0);
dll_make_first (&free_waiters, &w->nw.q);
ATM_STORE_REL (&free_waiters_mu, 0); /* release store */
/* Destroys waiter struct. */
void nsync_waiter_destroy_ (waiter *w) {
if (w->tag) {
nsync_mu_semaphore_destroy (&w->sem);
w->tag = 0;
}
}