1 files changed, 146 insertions, 0 deletions
diff --git a/kern/llsync.h b/kern/llsync.h
new file mode 100644
index 00000000..32987a03
--- /dev/null
+++ b/kern/llsync.h
@@ -0,0 +1,146 @@
+/*
+ * Copyright (c) 2013 Richard Braun.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *
+ * Lockless synchronization.
+ */
+
+#ifndef _KERN_LLSYNC_H
+#define _KERN_LLSYNC_H
+
+#include <kern/list.h>
+#include <kern/macros.h>
+#include <kern/llsync_i.h>
+#include <kern/thread.h>
+#include <machine/mb.h>
+
+struct llsync_work;
+
+/*
+ * Type for work functions.
+ *
+ * Works are guaranteed to process in thread context and can block, but
+ * must not sleep for long durations.
+ */
+typedef void (*llsync_fn_t)(struct llsync_work *);
+
+/*
+ * Deferred work.
+ *
+ * This structure should be embedded in objects protected with lockless
+ * synchronization. It stores the work function and is passed to it as its
+ * only parameter. The function can then find the containing object with
+ * structof and release it.
+ */
+struct llsync_work {
+    struct list node;
+    llsync_fn_t fn;
+};
+
+/*
+ * Safely assign a pointer.
+ *
+ * This macro enforces memory ordering. It should be used to reference
+ * objects once they're completely built, so that readers accessing the
+ * pointer obtain consistent data.
+ */
+#define llsync_assign_ptr(ptr, value)   \
+MACRO_BEGIN                             \
+    mb_store();                         \
+    (ptr) = (value);                    \
+MACRO_END
+
+/*
+ * Safely access a pointer.
+ *
+ * No memory barrier, rely on data dependency to enforce ordering.
+ */
+#define llsync_read_ptr(ptr) (ptr)
+
+static inline void
+llsync_read_lock(void)
+{
+    thread_preempt_disable();
+}
+
+static inline void
+llsync_read_unlock(void)
+{
+    thread_preempt_enable();
+}
+
+/*
+ * Reset the checkpoint flag of a processor.
+ *
+ * Called from interrupt context.
+ */
+static inline void
+llsync_reset_checkpoint(unsigned int cpu)
+{
+    llsync_cpu_checkpoints[cpu].checked = 0;
+}
+
+/*
+ * Report that a processor has reached a checkpoint.
+ *
+ * Called during context switch.
+ */
+static inline void
+llsync_checkin(unsigned int cpu)
+{
+    llsync_cpu_checkpoints[cpu].checked = 1;
+}
+
+/*
+ * Initialize the llsync module.
+ */
+void llsync_setup(void);
+
+/*
+ * Report that a processor will be regularly checking in.
+ */
+void llsync_register_cpu(unsigned int cpu);
+
+/*
+ * Report that a processor has entered a state in which checking in becomes
+ * irrelevant (e.g. the idle loop).
+ */
+void llsync_unregister_cpu(unsigned int cpu);
+
+/*
+ * Commit a pending checkpoint.
+ *
+ * Checking in is a light processor-local operation. Committing a checkpoint
+ * is a heavier global one, and is performed less often, normally during the
+ * system timer interrupt.
+ */
+void llsync_commit_checkpoint(unsigned int cpu);
+
+/*
+ * Defer an operation until all existing read-side references are dropped,
+ * without blocking.
+ */
+void llsync_defer(struct llsync_work *work, llsync_fn_t fn);
+
+/*
+ * Wait for all existing read-side references to be dropped.
+ *
+ * This function sleeps, and may do so for a moderately long duration (a few
+ * system timer ticks).
+ */
+void llsync_wait(void);
+
+#endif /* _KERN_LLSYNC_H */