SerialScheduler: added a single-threaded scheduler

Added a new scheduler for ensuring single-threaded
operation. Additionally, added a static assert to (at least for now)
restrict the use of tagging to this single threaded scheduler.

2 files changed, 69 insertions, 0 deletions

diff --git a/include/framework/DynamicExtension.h b/include/framework/DynamicExtension.h
index a1f7c2b..3a4a7e1 100644
--- a/include/framework/DynamicExtension.h
+++ b/include/framework/DynamicExtension.h
@@ -26,6 +26,7 @@
 
 #include "framework/util/Configuration.h"
 #include "framework/scheduling/FIFOScheduler.h"
+#include "framework/scheduling/SerialScheduler.h"
 #include "framework/scheduling/Epoch.h"
 
 #include "psu-util/timer.h"
@@ -82,6 +83,7 @@ public:
         // FIXME: delete tagging will require a lot of extra work to get
         //        operating "correctly" in a concurrent environment.
         if constexpr (D == DeletePolicy::TAGGING) {
+            static_assert(std::same_as<SCHED, SerialScheduler>, "Tagging is only supported in single-threaded operation");
             BufView buffers = get_active_epoch()->get_buffer_view();
 
             if (get_active_epoch()->get_structure()->tagged_delete(rec)) {
diff --git a/include/framework/scheduling/SerialScheduler.h b/include/framework/scheduling/SerialScheduler.h
new file mode 100644
index 0000000..9c767e8
--- /dev/null
+++ b/include/framework/scheduling/SerialScheduler.h
@@ -0,0 +1,67 @@
+/*
+ * include/framework/scheduling/SerialScheduler.h
+ *
+ * Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu>
+ *
+ * All rights reserved. Published under the Modified BSD License.
+ *
+ * IMPORTANT: This "scheduler" is a shim implementation for allowing
+ * strictly serial, single-threaded operation of the framework. It should 
+ * never be used in multi-threaded contexts. A call to the schedule_job 
+ * function will immediately run the job and block on its completion before
+ * returning.
+ *
+ */
+#pragma once
+
+#include <vector>
+#include <memory>
+#include <queue>
+#include <thread>
+#include <condition_variable>
+#include <future>
+
+#include "util/types.h"
+#include "framework/interface/Shard.h"
+#include "framework/interface/Query.h"
+#include "framework/interface/Record.h"
+#include "framework/structure/MutableBuffer.h"
+#include "framework/util/Configuration.h"
+#include "framework/structure/ExtensionStructure.h"
+#include "framework/scheduling/Task.h"
+
+namespace de {
+
+class SerialScheduler {
+public:
+    SerialScheduler(size_t memory_budget, size_t thread_cnt) 
+      : m_memory_budget((memory_budget) ? memory_budget : UINT64_MAX)
+      , m_thrd_cnt((thread_cnt) ? thread_cnt: UINT64_MAX)
+      , m_used_memory(0)
+      , m_used_thrds(0)
+      , m_counter(0)
+    {}
+
+    ~SerialScheduler() = default;
+
+    void schedule_job(std::function<void(void*)> job, size_t size, void *args) {
+        size_t ts = m_counter++;
+        auto t = Task(size, ts, job, args);
+        t();
+    }
+
+    void shutdown() {
+        /* intentionally left blank */
+    }
+
+private:
+    size_t m_memory_budget;
+    size_t m_thrd_cnt;
+
+    size_t m_used_thrds;
+    size_t m_used_memory;
+
+    size_t m_counter;
+};
+
+}