From 2eb2dddb59b47fadffd5e2922021bac841eb3f2e Mon Sep 17 00:00:00 2001
From: Calvin Rose <calsrose@gmail.com>
Date: Sun, 26 Jul 2020 23:45:25 -0500
Subject: [PATCH] Begin work on channels.

---
 src/core/ev.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/src/core/ev.c b/src/core/ev.c
index 27f64e7c..652a56d1 100644
--- a/src/core/ev.c
+++ b/src/core/ev.c
@@ -326,6 +326,72 @@ void janet_addtimeout(double sec) {
     add_timeout(to);
 }
 
+/* Channels */
+
+typedef struct {
+    int32_t capacity;
+    int32_t head;
+    int32_t tail;
+    JanetFiber **fibers;
+} JanetFiberQueue;
+
+#define JANET_MAX_FQ_CAPACITY 0xFFFFFF
+
+static void janet_fq_init(JanetFiberQueue *fq) {
+    fq->fibers = NULL;
+    fq->head = 0;
+    fq->tail = 0;
+    fq->capacity = 0;
+}
+
+static int32_t janet_fq_count(JanetFiberQueue *fq) {
+    return (fq->head > fq->tail)
+        ? (fq->tail + fq->capacity - fq->head)
+        : (fq->tail - fq->head);
+}
+
+static int janet_fq_push(JanetFiberQueue *fq, JanetFiber *fiber) {
+    int32_t count = janet_fq_count(fq);
+    if (count + 1 == JANET_MAX_FQ_CAPACITY) return 1;
+    /* Resize if needed */
+    if (count + 1 > fq->capacity) {
+        int32_t newcap = (count + 1) * 2;
+        if (newcap > JANET_MAX_FQ_CAPACITY) newcap = JANET_MAX_FQ_CAPACITY;
+        if (fq->head > fq->tail) {
+            /* Two segments, we need to allocate and memcpy x2 */
+            JanetFiber **newfibers = malloc(sizeof(JanetFiber *) * newcap);
+            if (NULL == newfibers) {
+                JANET_OUT_OF_MEMORY;
+            }
+            int32_t seg1 = fq->capacity - fq->head;
+            int32_t seq2 = fq->tail;
+            memcpy(newfibers, fq->fibers + fq->head, seg1 * sizeof(JanetFiber *));
+            memcpy(newfibers + seg1, fq->fibers, seq2 * sizeof(JanetFiber *));
+            free(fq->fibers);
+            fq->fibers = newfibers;
+            fq->head = 0;
+            fq->tail = count;
+        } else {
+            /* One segment, we can just realloc */
+            fq->fibers = realloc(fq->fibers, sizeof(JanetFiber *) * newcap);
+            if (NULL == fq->fibers) {
+                JANET_OUT_OF_MEMORY;
+            }
+        }
+        fq->capacity = newcap;
+    }
+    fq->fibers[fq->tail++] = fiber;
+    if (fq->tail >= fq->capacity) fq->tail = 0;
+    return 0;
+}
+
+static int janet_fq_pop(JanetFiberQueue *fq, JanetFiber **out) {
+    if (fq->head == fq->tail) return 1;
+    *out = fq->fibers[fq->head++];
+    if (fq->head >= fq->capacity) fq->head = 0;
+    return 0;
+}
+
 /* Main event loop */
 
 void janet_loop1_impl(void);