1 files changed, 118 insertions, 0 deletions
diff --git a/lib/pullwr.h b/lib/pullwr.h
new file mode 100644
index 0000000..a0e89e0
--- /dev/null
+++ b/lib/pullwr.h
@@ -0,0 +1,118 @@
+/*
+ * Pull-driven write event handler
+ * Copyright (C) 2019  David Lamparter
+ *
+ * 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 2 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; see the file COPYING; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef _WRITEPOLL_H
+#define _WRITEPOLL_H
+
+#include <stdbool.h>
+#include <stdint.h>
+
+#include "thread.h"
+#include "stream.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct pullwr;
+
+/* This is a "pull-driven" write event handler.  Instead of having some buffer
+ * or being driven by the availability of data, it triggers on the space being
+ * available on the socket for data to be written on and then calls fill() to
+ * get data to be sent.
+ *
+ * pullwr_* maintains an "idle" vs. "active" state, going into idle when a
+ * fill() call completes without feeing more data into it.  The overall
+ * semantics are:
+ * - to put data out, call pullwr_write().  This is possible from both inside
+ *   fill() callbacks or anywhere else.  Doing so puts the pullwr into
+ *   active state.
+ * - in active state, the fill() callback will be called and should feed more
+ *   data in.  It should NOT loop to push out more than one "unit" of data;
+ *   the pullwr code handles this by calling fill() until it has enough data.
+ * - if there's nothing more to be sent, fill() returns without doing anything
+ *   and pullwr goes into idle state after flushing all buffered data out.
+ * - when new data becomes available, pullwr_bump() should be called to put
+ *   the pullwr back into active mode so it will collect data from fill(),
+ *   or you can directly call pullwr_write().
+ * - only calling pullwr_write() from within fill() is the cleanest way of
+ *   doing things.
+ *
+ * When the err() callback is called, the pullwr should be considered unusable
+ * and released with pullwr_del().  This can be done from inside the callback,
+ * the pullwr code holds no more references on it when calling err().
+ */
+extern struct pullwr *_pullwr_new(struct thread_master *tm, int fd,
+		void *arg,
+		void (*fill)(void *, struct pullwr *),
+		void (*err)(void *, struct pullwr *, bool eof));
+extern void pullwr_del(struct pullwr *pullwr);
+
+/* type-checking wrapper.  makes sure fill() and err() take a first argument
+ * whose type is identical to the type of arg.
+ * => use "void fill(struct mystruct *arg, ...)" - no "void *arg"
+ */
+#define pullwr_new(tm, fd, arg, fill, err) ({                                  \
+	void (*fill_typechk)(typeof(arg), struct pullwr *) = fill;          \
+	void (*err_typechk)(typeof(arg), struct pullwr *, bool) = err;      \
+	_pullwr_new(tm, fd, arg, (void *)fill_typechk, (void *)err_typechk);   \
+})
+
+/* max_spin_usec is the time after which the pullwr event handler will stop
+ *   trying to get more data from fill() and yield control back to the
+ *   thread_master.  It does reschedule itself to continue later; this is
+ *   only to make sure we don't freeze the entire process if we're piping a
+ *   lot of data to a local endpoint that reads quickly (i.e. no backpressure)
+ *
+ *   default: 2500 (2.5 ms)
+ *
+ * write_threshold is the amount of data buffered from fill() calls at which
+ *   the pullwr code starts calling write().  But this is not a "limit".
+ *   pullwr will keep poking fill() for more data until
+ *   (a) max_spin_usec is reached; fill() will be called again later after
+ *       returning to the thread_master to give other events a chance to run
+ *   (b) fill() returns without pushing any data onto the pullwr with
+ *       pullwr_write(), so fill() will NOT be called again until a call to
+ *       pullwr_bump() or pullwr_write() comes in.
+ *
+ *   default: 16384 (16 kB)
+ *
+ * passing 0 for either value (or not calling it at all) uses the default.
+ */
+extern void pullwr_cfg(struct pullwr *pullwr, int64_t max_spin_usec,
+		       size_t write_threshold);
+
+extern void pullwr_bump(struct pullwr *pullwr);
+extern void pullwr_write(struct pullwr *pullwr,
+		const void *data, size_t len);
+
+static inline void pullwr_write_stream(struct pullwr *pullwr,
+		struct stream *s)
+{
+	pullwr_write(pullwr, s->data, stream_get_endp(s));
+}
+
+extern void pullwr_stats(struct pullwr *pullwr, uint64_t *total_written,
+			 size_t *pending, size_t *kernel_pending);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* _WRITEPOLL_H */