1 files changed, 32 insertions, 0 deletions
diff --git a/research/experiments/021-memory/hold-surface.c b/research/experiments/021-memory/hold-surface.c
new file mode 100644
index 0000000..c1c2d4b
--- /dev/null
+++ b/research/experiments/021-memory/hold-surface.c
@@ -0,0 +1,32 @@
+/* A surface that holds a snapshot until the server stops: a reader that
+ * never lets go, for run.py's held case (research/experiments/021-memory).
+ * It holds the first snapshot whose number view VIEW is at least AT (the
+ * first snapshot at all without them), and lets every other one go.
+ *
+ *   pure-serve ... --surface hold-surface.so [-- VIEW AT] */
+#include "surface.h"
+#include <poll.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int pure_surface_run(const PureSurface *s, int argc, char **argv) {
+    static PureApp reader;
+    int view = argc > 2 ? pure_module_view(s->module, argv[1]) : -1;
+    double at = argc > 2 ? atof(argv[2]) : 0, value = 0;
+    PureSnapshot *held = NULL;
+    while (!s->stopping(s->host)) {
+        struct pollfd wait = {s->changes, POLLIN, 0};
+        if (poll(&wait, 1, 20) > 0 && (wait.revents & POLLIN)) {
+            uint64_t saves;
+            if (read(s->changes, &saves, sizeof(saves)) < 0) { /* cleared already */ }
+        }
+        if (held) continue;
+        PureSnapshot *read_now = s->read(s->host, &reader);
+        if (!read_now) continue;
+        if (view < 0 || (pure_app_view(&reader, (uint32_t)view, &value) && value >= at)) held = read_now;
+        else s->release(s->host, read_now);
+    }
+    if (held) s->release(s->host, held);
+    return 0;
+}