1 files changed, 148 insertions, 0 deletions
diff --git a/web/server/web_client_cache.c b/web/server/web_client_cache.c
new file mode 100644
index 00000000..364fc76b
--- /dev/null
+++ b/web/server/web_client_cache.c
@@ -0,0 +1,148 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#define WEB_SERVER_INTERNALS 1
+#include "web_client_cache.h"
+
+// ----------------------------------------------------------------------------
+// allocate and free web_clients
+
+// ----------------------------------------------------------------------------
+// web clients caching
+
+// When clients connect and disconnect, avoid allocating and releasing memory.
+// Instead, when new clients get connected, reuse any memory previously allocated
+// for serving web clients that are now disconnected.
+
+// The size of the cache is adaptive. It caches the structures of 2x
+// the number of currently connected clients.
+
+static struct clients_cache {
+    struct {
+        SPINLOCK spinlock;
+        struct web_client *head;    // the structures of the currently connected clients
+        size_t count;               // the count the currently connected clients
+
+        size_t allocated;           // the number of allocations
+        size_t reused;              // the number of re-uses
+    } used;
+
+    struct {
+        SPINLOCK spinlock;
+        struct web_client *head;    // the cached structures, available for future clients
+        size_t count;               // the number of cached structures
+    } avail;
+} web_clients_cache = {
+        .used = {
+                .spinlock = NETDATA_SPINLOCK_INITIALIZER,
+                .head = NULL,
+                .count = 0,
+                .reused = 0,
+                .allocated = 0,
+        },
+        .avail = {
+                .spinlock = NETDATA_SPINLOCK_INITIALIZER,
+                .head = NULL,
+                .count = 0,
+        },
+};
+
+// destroy the cache and free all the memory it uses
+void web_client_cache_destroy(void) {
+    internal_error(true, "web_client_cache has %zu used and %zu available clients, allocated %zu, reused %zu (hit %zu%%)."
+        , web_clients_cache.used.count
+        , web_clients_cache.avail.count
+        , web_clients_cache.used.allocated
+        , web_clients_cache.used.reused
+        , (web_clients_cache.used.allocated + web_clients_cache.used.reused)?(web_clients_cache.used.reused * 100 / (web_clients_cache.used.allocated + web_clients_cache.used.reused)):0
+        );
+
+    struct web_client *w, *t;
+
+    spinlock_lock(&web_clients_cache.avail.spinlock);
+    w = web_clients_cache.avail.head;
+    while(w) {
+        t = w;
+        w = w->cache.next;
+        web_client_free(t);
+    }
+    web_clients_cache.avail.head = NULL;
+    web_clients_cache.avail.count = 0;
+    spinlock_unlock(&web_clients_cache.avail.spinlock);
+
+// DO NOT FREE THEM IF THEY ARE USED
+//    spinlock_lock(&web_clients_cache.used.spinlock);
+//    w = web_clients_cache.used.head;
+//    while(w) {
+//        t = w;
+//        w = w->next;
+//        web_client_free(t);
+//    }
+//    web_clients_cache.used.head = NULL;
+//    web_clients_cache.used.count = 0;
+//    web_clients_cache.used.reused = 0;
+//    web_clients_cache.used.allocated = 0;
+//    spinlock_unlock(&web_clients_cache.used.spinlock);
+}
+
+struct web_client *web_client_get_from_cache(void) {
+    spinlock_lock(&web_clients_cache.avail.spinlock);
+    struct web_client *w = web_clients_cache.avail.head;
+    if(w) {
+        // get it from avail
+        DOUBLE_LINKED_LIST_REMOVE_ITEM_UNSAFE(web_clients_cache.avail.head, w, cache.prev, cache.next);
+        web_clients_cache.avail.count--;
+
+        spinlock_unlock(&web_clients_cache.avail.spinlock);
+        web_client_reuse_from_cache(w);
+        spinlock_lock(&web_clients_cache.used.spinlock);
+
+        web_clients_cache.used.reused++;
+    }
+    else {
+        spinlock_unlock(&web_clients_cache.avail.spinlock);
+        w = web_client_create(&netdata_buffers_statistics.buffers_web);
+        spinlock_lock(&web_clients_cache.used.spinlock);
+
+        w->id = global_statistics_web_client_connected();
+        web_clients_cache.used.allocated++;
+    }
+
+    // link it to used web clients
+    DOUBLE_LINKED_LIST_PREPEND_ITEM_UNSAFE(web_clients_cache.used.head, w, cache.prev, cache.next);
+    web_clients_cache.used.count++;
+    spinlock_unlock(&web_clients_cache.used.spinlock);
+
+    // initialize it
+    w->use_count++;
+    w->mode = WEB_CLIENT_MODE_GET;
+    memset(w->transaction, 0, sizeof(w->transaction));
+
+    return w;
+}
+
+void web_client_release_to_cache(struct web_client *w) {
+
+#ifdef ENABLE_HTTPS
+    netdata_ssl_close(&w->ssl);
+#endif
+
+    // unlink it from the used
+    spinlock_lock(&web_clients_cache.used.spinlock);
+    DOUBLE_LINKED_LIST_REMOVE_ITEM_UNSAFE(web_clients_cache.used.head, w, cache.prev, cache.next);
+    ssize_t used_count = (ssize_t)--web_clients_cache.used.count;
+    spinlock_unlock(&web_clients_cache.used.spinlock);
+
+    spinlock_lock(&web_clients_cache.avail.spinlock);
+    if(w->use_count > 100 || (used_count > 0 && web_clients_cache.avail.count >= 2 * (size_t)used_count) || (used_count <= 10 && web_clients_cache.avail.count >= 20)) {
+        spinlock_unlock(&web_clients_cache.avail.spinlock);
+
+        // we have too many of them - free it
+        web_client_free(w);
+    }
+    else {
+        // link it to the avail
+        DOUBLE_LINKED_LIST_PREPEND_ITEM_UNSAFE(web_clients_cache.avail.head, w, cache.prev, cache.next);
+        web_clients_cache.avail.count++;
+        spinlock_unlock(&web_clients_cache.avail.spinlock);
+    }
+}