feat: further lay groundwork for worker threads

include/lnm/loop.h

@@ -1,6 +1,7 @@
 #ifndef LNM_LOOP
 #define LNM_LOOP
 
+#include <pthread.h>
 #include <stdatomic.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -9,12 +10,17 @@
 
 #define LNM_LOOP_BUF_SIZE 2048
 
-typedef enum {
+typedef enum lnm_loop_state {
   lnm_loop_state_req = 0,
   lnm_loop_state_res,
   lnm_loop_state_end,
+  lnm_loop_state_req_blocking,
+  lnm_loop_state_res_blocking,
 } lnm_loop_state;
 
+/**
+ * State for a currently active connection
+ */
 typedef struct lnm_loop_conn {
   int fd;
   lnm_loop_state state;
@@ -30,6 +36,37 @@ typedef struct lnm_loop_conn {
   } w;
 } lnm_loop_conn;
 
+/**
+ * Concurrent fixed-size queue used to distribute work among worker threads
+ */
+typedef struct lnm_loop_queue {
+  struct {
+    lnm_loop_conn **arr;
+    size_t len;
+  } buf;
+  size_t head;
+  size_t tail;
+  pthread_mutex_t mutex;
+  pthread_cond_t cond;
+} lnm_loop_queue;
+
+/**
+ * Initialize a new queue with the specified fixed capacity
+ */
+lnm_err lnm_loop_queue_init(lnm_loop_queue **out, size_t cap);
+
+/**
+ * Queue the given connection. If the queue is currently full, this action
+ * blocks until there is space available.
+ */
+void lnm_loop_queue_push(lnm_loop_queue *q, lnm_loop_conn *conn);
+
+/**
+ * Pop a connection from the queue. This action blocks until a connection is
+ * available.
+ */
+lnm_loop_conn *lnm_loop_queue_pop(lnm_loop_queue *q);
+
 typedef struct lnm_loop {
   int listen_fd;
   int epoll_fd;
@@ -39,6 +76,7 @@ typedef struct lnm_loop {
   void (*ctx_free)(void *ctx);
   void (*data_read)(lnm_loop_conn *conn);
   void (*data_write)(lnm_loop_conn *conn);
+  lnm_loop_queue *wq;
 } lnm_loop;
 
 lnm_err lnm_loop_init(lnm_loop **out, void *gctx,
@@ -51,4 +89,15 @@ lnm_err lnm_loop_setup(lnm_loop *l, uint16_t port);
 
 lnm_err lnm_loop_run(lnm_loop *l, int thread_count);
 
+/**
+ * Reschedule the given connection, either on the event loop for network IO or
+ * on a worker thread for blocking work. Connections are terminated as needed.
+ */
+void lnm_loop_conn_schedule(lnm_loop *l, lnm_loop_conn *conn);
+
+/**
+ * Main loop executed on the worker threads.
+ */
+void lnm_loop_worker_run(void *arg);
+
 #endif

src/loop/lnm_loop.c

@@ -62,6 +62,10 @@ lnm_err lnm_loop_accept(lnm_loop *l) {
 
   l->open++;
 
+  // Make sure to re-arm the listening socket after accepting
+  event.data.ptr = NULL;
+  epoll_ctl(l->epoll_fd, EPOLL_CTL_MOD, l->listen_fd, &event);
+
   lnm_ldebug(section, "connection opened with fd %i", conn_fd);
 
   return lnm_err_ok;
@@ -123,6 +127,36 @@ lnm_err lnm_loop_setup(lnm_loop *l, uint16_t port) {
   return lnm_err_ok;
 }
 
+void lnm_loop_conn_schedule(lnm_loop *l, lnm_loop_conn *conn) {
+  switch (conn->state) {
+  // IO states get rescheduled in the epoll loop
+  case lnm_loop_state_req:
+  case lnm_loop_state_res: {
+    struct epoll_event event = {
+        .data.ptr = conn,
+        .events = (conn->state == lnm_loop_state_req ? EPOLLIN : EPOLLOUT) |
+                  EPOLLET | EPOLLONESHOT};
+
+    epoll_ctl(l->epoll_fd, EPOLL_CTL_MOD, conn->fd, &event);
+  } break;
+  case lnm_loop_state_req_blocking:
+  case lnm_loop_state_res_blocking:
+    lnm_loop_queue_push(l->wq, conn);
+    break;
+  case lnm_loop_state_end: {
+    int conn_fd = conn->fd;
+
+    lnm_loop_conn_free(l, conn);
+    close(conn_fd);
+    l->open--;
+
+    epoll_ctl(l->epoll_fd, EPOLL_CTL_DEL, conn_fd, NULL);
+
+    lnm_ldebug(section, "connection closed with fd %i", conn_fd);
+  } break;
+  }
+}
+
 typedef struct lnm_loop_thread_args {
   lnm_loop *l;
   int id;
@@ -143,9 +177,6 @@ lnm_err lnm_loop_run_thread(lnm_loop_thread_args *args) {
 
   lnm_linfo(section, "thread %i started", thread_id);
 
-  struct epoll_event listen_event = {
-      .data.ptr = NULL, .events = EPOLLIN | EPOLLET | EPOLLONESHOT};
-
   while (1) {
     int polled = epoll_wait(l->epoll_fd, events, events_cap, -1);
     lnm_ldebug(section, "polled (thread %i): %i", thread_id, polled);
@@ -157,30 +188,12 @@ lnm_err lnm_loop_run_thread(lnm_loop_thread_args *args) {
     for (int i = 0; i < polled; i++) {
       if (events[i].data.ptr == NULL) {
         lnm_loop_accept(l);
-
-        epoll_ctl(l->epoll_fd, EPOLL_CTL_MOD, l->listen_fd, &listen_event);
       } else {
         lnm_loop_conn *conn = events[i].data.ptr;
+
+        // At this point, state is always an IO state
         lnm_loop_conn_io(l, conn);
-
-        if (conn->state == lnm_loop_state_end) {
-          int conn_fd = conn->fd;
-
-          lnm_loop_conn_free(l, conn);
-          close(conn_fd);
-          l->open--;
-
-          epoll_ctl(l->epoll_fd, EPOLL_CTL_DEL, conn_fd, NULL);
-
-          lnm_ldebug(section, "connection closed with fd %i", conn_fd);
-        } else {
-          struct epoll_event event = {
-              .data.ptr = conn,
-              .events =
-                  (conn->state == lnm_loop_state_req ? EPOLLIN : EPOLLOUT) |
-                  EPOLLET | EPOLLONESHOT};
-          epoll_ctl(l->epoll_fd, EPOLL_CTL_MOD, conn->fd, &event);
-        }
+        lnm_loop_conn_schedule(l, conn);
       }
     }
 

src/loop/lnm_loop_worker.c

@@ -0,0 +1,84 @@
+#include <sys/epoll.h>
+
+#include "lnm/loop.h"
+
+lnm_err lnm_loop_queue_init(lnm_loop_queue **out, size_t cap) {
+  lnm_loop_conn **arr = malloc(cap * sizeof(lnm_loop_conn *));
+
+  if (arr == NULL) {
+    return lnm_err_failed_alloc;
+  }
+
+  lnm_loop_queue *q = calloc(1, sizeof(lnm_loop_queue));
+
+  if (q == NULL) {
+    free(arr);
+
+    return lnm_err_failed_alloc;
+  }
+
+  q->buf.arr = arr;
+  q->buf.len = cap;
+
+  pthread_mutex_init(&q->mutex, NULL);
+  pthread_cond_init(&q->cond, NULL);
+
+  *out = q;
+
+  return lnm_err_ok;
+}
+
+void lnm_loop_queue_push(lnm_loop_queue *q, lnm_loop_conn *conn) {
+  pthread_mutex_lock(&q->mutex);
+
+  while (q->tail == q->head) {
+    pthread_cond_wait(&q->cond, &q->mutex);
+  }
+
+  q->buf.arr[q->tail] = conn;
+
+  // Make sure the index wraps around
+  q->tail = (q->tail + 1) % q->buf.len;
+
+  // Unlock mutex and signal to waiting threads
+  pthread_mutex_unlock(&q->mutex);
+  pthread_cond_signal(&q->cond);
+}
+
+lnm_loop_conn *lnm_loop_queue_pop(lnm_loop_queue *q) {
+  pthread_mutex_lock(&q->mutex);
+
+  while (q->tail == q->head) {
+    pthread_cond_wait(&q->cond, &q->mutex);
+  }
+
+  lnm_loop_conn *out = q->buf.arr[q->head];
+  q->head = (q->head + 1) % q->buf.len;
+
+  // Unlock mutex and signal to waiting threads
+  pthread_mutex_unlock(&q->mutex);
+  pthread_cond_signal(&q->cond);
+
+  return out;
+}
+
+void lnm_loop_worker_run(void *arg) {
+  lnm_loop *l = arg;
+  lnm_loop_queue *q = l->wq;
+
+  while (1) {
+    lnm_loop_conn *conn = lnm_loop_queue_pop(q);
+
+    switch (conn->state) {
+    case lnm_loop_state_req_blocking:
+      l->data_read(conn);
+      break;
+    case lnm_loop_state_res_blocking:
+      l->data_write(conn);
+    // Other states shouldn't even end up here, so we ignore them
+    default:;
+    }
+
+    lnm_loop_conn_schedule(l, conn);
+  }
+}