Take the sending loop out of the links, for the wires to join it (017, 2b)

link/sending.c is the process's sending loop: a sender joins it with its
round and the socket it waits on, and is rounded when its socket is
ready, when pushed, and when its time comes. Links are its first
senders; nothing they do changed. Events of a sender that left while the
loop waited are let go (the epoll is level-triggered: the others' come
again).

1 files changed, 160 insertions, 0 deletions

diff --git a/link/sending.c b/link/sending.c
new file mode 100644
index 0000000..f14dfc2
--- /dev/null
+++ b/link/sending.c
@@ -0,0 +1,160 @@
+#define _GNU_SOURCE
+#include "sending.h"
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/epoll.h>
+#include <sys/eventfd.h>
+#include <time.h>
+#include <unistd.h>
+
+#define MS UINT64_C(1000000)
+
+uint64_t pure_sending_now(void) {
+    struct timespec t;
+    clock_gettime(CLOCK_MONOTONIC, &t);
+    return (uint64_t)t.tv_sec * 1000000000u + (uint64_t)t.tv_nsec;
+}
+
+/* The loop: its senders under the lock, which it holds over its rounds. A
+ * push wakes it only when it sleeps, once: pushed tells it a sender was
+ * (it then does not sleep), sleeping that it is about to, signaled that it
+ * was woken. A sender that left while it waited may be in the events it
+ * got: those are let go (left counts the leaves), and come again. */
+static struct {
+    pthread_mutex_t lock;
+    PureSending *first;
+    int epoll, wake;
+    pthread_t thread;
+    bool running, stopping;
+    uint64_t left;
+    _Atomic bool pushed, sleeping, signaled;
+} loop = {.lock = PTHREAD_MUTEX_INITIALIZER, .epoll = -1, .wake = -1};
+
+static void wake(void) {
+    uint64_t one = 1;
+    if (loop.wake >= 0 && write(loop.wake, &one, sizeof(one)) != sizeof(one)) { /* full: it is readable already */ }
+}
+
+void pure_sending_init(PureSending *s, uint64_t (*round)(PureSending *, uint32_t ready)) {
+    memset(s, 0, sizeof(*s));
+    s->round = round;
+    s->fd = -1;
+}
+
+void pure_sending_push(PureSending *s) {
+    atomic_store(&s->pushed, true);
+    atomic_store(&loop.pushed, true);
+    if (atomic_load(&loop.sleeping) && !atomic_exchange(&loop.signaled, true)) wake();
+}
+
+static void watch_now(PureSending *s, int fd, uint32_t events) {
+    if (s->watched && (fd != s->fd || !events)) {
+        epoll_ctl(loop.epoll, EPOLL_CTL_DEL, s->fd, NULL);
+        s->watched = false;
+    }
+    if (fd >= 0 && events) {
+        struct epoll_event event = {.events = events, .data.ptr = s};
+        s->watched = !epoll_ctl(loop.epoll, s->watched ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &event);
+    }
+}
+
+void pure_sending_watch(PureSending *s, int fd, uint32_t events) {
+    if (s->joined && (fd != s->fd || events != s->events || (fd >= 0 && events && !s->watched))) watch_now(s, fd, events);
+    s->fd = fd;
+    s->events = events;
+}
+
+static void *run(void *context) {
+    (void)context;
+    struct epoll_event events[64];
+    int timeout = 0;
+    pthread_mutex_lock(&loop.lock);
+    uint64_t left = loop.left;
+    pthread_mutex_unlock(&loop.lock);
+    for (;;) {
+        atomic_store(&loop.sleeping, true);
+        if (atomic_load(&loop.pushed)) timeout = 0; /* pushed since: no sleep */
+        int ready = epoll_wait(loop.epoll, events, 64, timeout);
+        atomic_store(&loop.sleeping, false);
+        atomic_store(&loop.signaled, false);
+        atomic_store(&loop.pushed, false);
+        pthread_mutex_lock(&loop.lock);
+        if (loop.stopping) {
+            pthread_mutex_unlock(&loop.lock);
+            break;
+        }
+        bool again = ready > 0 && left != loop.left; /* one may be gone: its events let go, the others' come again */
+        for (int e = 0; e < ready; ++e) {
+            PureSending *s = events[e].data.ptr;
+            if (!s) {
+                uint64_t signals;
+                if (read(loop.wake, &signals, sizeof(signals)) < 0) { /* cleared already */ }
+            } else if (!again) s->ready |= events[e].events;
+        }
+        uint64_t soonest = 0, now = pure_sending_now();
+        for (PureSending *s = loop.first; s; s = s->next) {
+            bool pushed = atomic_exchange(&s->pushed, false); /* pushed after: the next round's */
+            if (s->ready || pushed || (s->due && s->due <= now)) {
+                uint32_t was = s->ready;
+                s->ready = 0;
+                s->due = s->round(s, was);
+            }
+            if (s->due && (!soonest || s->due < soonest)) soonest = s->due;
+        }
+        left = loop.left;
+        pthread_mutex_unlock(&loop.lock);
+        timeout = again ? 0 : !soonest ? -1 : soonest <= now ? 0 : (int)((soonest - now) / MS) + 1;
+    }
+    return NULL;
+}
+
+bool pure_sending_join(PureSending *s, char *error, size_t size) {
+    pthread_mutex_lock(&loop.lock);
+    bool ok = loop.running;
+    if (!ok) { /* the first: the loop */
+        loop.stopping = false;
+        struct epoll_event event = {.events = EPOLLIN, .data.ptr = NULL};
+        ok = (loop.epoll >= 0 || (loop.epoll = epoll_create1(EPOLL_CLOEXEC)) >= 0) &&
+             (loop.wake >= 0 || ((loop.wake = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC)) >= 0 &&
+                                 !epoll_ctl(loop.epoll, EPOLL_CTL_ADD, loop.wake, &event))) &&
+             !pthread_create(&loop.thread, NULL, run, NULL);
+        if (ok) pthread_setname_np(loop.thread, "pure-send"); /* the sends' CPU, seen apart */
+        loop.running = ok;
+    }
+    if (ok) {
+        s->joined = true;
+        if (s->fd >= 0 && s->events) watch_now(s, s->fd, s->events);
+        s->next = loop.first;
+        loop.first = s;
+        atomic_store(&s->pushed, true); /* a first round */
+        atomic_store(&loop.pushed, true);
+    }
+    pthread_mutex_unlock(&loop.lock);
+    if (!ok) {
+        snprintf(error, size, "the sending loop cannot be made");
+        return false;
+    }
+    wake();
+    return true;
+}
+
+void pure_sending_leave(PureSending *s) {
+    if (!s->joined) return;
+    pthread_mutex_lock(&loop.lock);
+    for (PureSending **at = &loop.first; *at; at = &(*at)->next)
+        if (*at == s) {
+            *at = s->next;
+            break;
+        }
+    if (s->watched) epoll_ctl(loop.epoll, EPOLL_CTL_DEL, s->fd, NULL);
+    s->watched = s->joined = false;
+    ++loop.left;
+    bool last = !loop.first && loop.running;
+    if (last) loop.stopping = true, loop.running = false;
+    pthread_mutex_unlock(&loop.lock);
+    if (last) { /* the last: the loop stops */
+        wake();
+        pthread_join(loop.thread, NULL);
+    }
+}