Merge remote-tracking branch 'fancycode/buffer_references'

Conflicts:
	buffer.c

buffer.c

@@ -150,7 +150,7 @@ static struct evbuffer_chain *evbuffer_expand_singlechain(struct evbuffer *buf,
 static int evbuffer_ptr_subtract(struct evbuffer *buf, struct evbuffer_ptr *pos,
     size_t howfar);
 static int evbuffer_file_segment_materialize(struct evbuffer_file_segment *seg);
-
+static inline void evbuffer_chain_incref(struct evbuffer_chain *chain);
 
 static struct evbuffer_chain *
 evbuffer_chain_new(size_t size)
@@ -178,17 +178,29 @@ evbuffer_chain_new(size_t size)
 	 */
 	chain->buffer = EVBUFFER_CHAIN_EXTRA(u_char, chain);
 
+	chain->refcnt = 1;
+
 	return (chain);
 }
 
 static inline void
 evbuffer_chain_free(struct evbuffer_chain *chain)
 {
+	EVUTIL_ASSERT(chain->refcnt > 0);
+	if (--chain->refcnt > 0) {
+		// chain is still referenced by other chains
+		return;
+	}
+	
 	if (CHAIN_PINNED(chain)) {
+		// will get freed once no longer dangling
+		chain->refcnt++;
 		chain->flags |= EVBUFFER_DANGLING;
 		return;
 	}
-
+	
+	// safe to release chain, it's either a referencing
+	// chain or all references to it have been freed
 	if (chain->flags & EVBUFFER_REFERENCE) {
 		struct evbuffer_chain_reference *info =
 		    EVBUFFER_CHAIN_EXTRA(
@@ -212,6 +224,21 @@ evbuffer_chain_free(struct evbuffer_chain *chain)
 			evbuffer_file_segment_free(info->segment);
 		}
 	}
+	if (chain->flags & EVBUFFER_MULTICAST) {
+		struct evbuffer_multicast_parent *info =
+		    EVBUFFER_CHAIN_EXTRA(
+			    struct evbuffer_multicast_parent,
+			    chain);
+		// referencing chain is being freed, decrease
+		// refcounts of source chain and associated
+		// evbuffer (which get freed once both reach
+		// zero)
+		EVUTIL_ASSERT(info->source != NULL);
+		EVUTIL_ASSERT(info->parent != NULL);
+		EVBUFFER_LOCK(info->source);
+		evbuffer_chain_free(info->parent);
+		_evbuffer_decref_and_unlock(info->source);
+	}
 
 	mm_free(chain);
 }
@@ -316,6 +343,12 @@ _evbuffer_chain_unpin(struct evbuffer_chain *chain, unsigned flag)
 		evbuffer_chain_free(chain);
 }
 
+static inline void
+evbuffer_chain_incref(struct evbuffer_chain *chain)
+{
+    ++chain->refcnt;
+}
+
 struct evbuffer *
 evbuffer_new(void)
 {
@@ -853,6 +886,46 @@ APPEND_CHAIN(struct evbuffer *dst, struct evbuffer *src)
 	dst->total_len += src->total_len;
 }
 
+static inline void
+APPEND_CHAIN_MULTICAST(struct evbuffer *dst, struct evbuffer *src)
+{
+	struct evbuffer_chain *tmp;
+	struct evbuffer_chain *chain = src->first;
+	struct evbuffer_multicast_parent *extra;
+
+	ASSERT_EVBUFFER_LOCKED(dst);
+	ASSERT_EVBUFFER_LOCKED(src);
+
+	for (; chain; chain = chain->next) {
+		if (!chain->off || chain->flags & EVBUFFER_DANGLING) {
+			// skip empty chains
+			continue;
+		}
+
+		tmp = evbuffer_chain_new(sizeof(struct evbuffer_multicast_parent));
+		if (!tmp) {
+			event_warn("%s: out of memory", __func__);
+			return;
+		}
+		extra = EVBUFFER_CHAIN_EXTRA(struct evbuffer_multicast_parent, tmp);
+		// reference evbuffer containing source chain so it
+		// doesn't get released while the chain is still
+		// being referenced to
+		_evbuffer_incref(src);
+		extra->source = src;
+		// reference source chain which now becomes immutable
+		evbuffer_chain_incref(chain);
+		extra->parent = chain;
+		chain->flags |= EVBUFFER_IMMUTABLE;
+		tmp->buffer_len = chain->buffer_len;
+		tmp->misalign = chain->misalign;
+		tmp->off = chain->off;
+		tmp->flags |= EVBUFFER_MULTICAST|EVBUFFER_IMMUTABLE;
+		tmp->buffer = chain->buffer;
+		evbuffer_chain_insert(dst, tmp);
+	}
+}
+
 static void
 PREPEND_CHAIN(struct evbuffer *dst, struct evbuffer *src)
 {
@@ -917,6 +990,49 @@ done:
 	return result;
 }
 
+int
+evbuffer_add_buffer_reference(struct evbuffer *outbuf, struct evbuffer *inbuf)
+{
+	size_t in_total_len, out_total_len;
+	struct evbuffer_chain *chain;
+	int result = 0;
+
+	EVBUFFER_LOCK2(inbuf, outbuf);
+	in_total_len = inbuf->total_len;
+	out_total_len = outbuf->total_len;
+	chain = inbuf->first;
+
+	if (in_total_len == 0)
+		goto done;
+
+	if (outbuf->freeze_end || outbuf == inbuf) {
+		result = -1;
+		goto done;
+	}
+
+	for (; chain; chain = chain->next) {
+		if ((chain->flags & (EVBUFFER_FILESEGMENT|EVBUFFER_SENDFILE|EVBUFFER_MULTICAST)) != 0) {
+			// chain type can not be referenced
+			result = -1;
+			goto done;
+		}
+	}
+
+	if (out_total_len == 0) {
+		/* There might be an empty chain at the start of outbuf; free
+		 * it. */
+		evbuffer_free_all_chains(outbuf->first);
+	}
+	APPEND_CHAIN_MULTICAST(outbuf, inbuf);
+
+	outbuf->n_add_for_cb += in_total_len;
+	evbuffer_invoke_callbacks(outbuf);
+
+done:
+	EVBUFFER_UNLOCK2(inbuf, outbuf);
+	return result;
+}
+
 int
 evbuffer_prepend_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf)
 {

evbuffer-internal.h

@@ -185,6 +185,11 @@ struct evbuffer_chain {
 	/** a chain that should be freed, but can't be freed until it is
 	 * un-pinned. */
 #define EVBUFFER_DANGLING	0x0040
+	/** a chain that is a referenced copy of another chain */
+#define EVBUFFER_MULTICAST	0x0080
+
+	/** number of references to this chain */
+	int refcnt;
 
 	/** Usually points to the read-write memory belonging to this
 	 * buffer allocated as part of the evbuffer_chain allocation.
@@ -243,6 +248,15 @@ struct evbuffer_file_segment {
 	ev_off_t length;
 };
 
+/** Information about the multicast parent of a chain.  Lives at the
+ * end of an evbuffer_chain with the EVBUFFER_MULTICAST flag set.  */
+struct evbuffer_multicast_parent {
+	/** source buffer the multicast parent belongs to */
+	struct evbuffer *source;
+	/** multicast parent for this chain */
+	struct evbuffer_chain *parent;
+};
+
 #define EVBUFFER_CHAIN_SIZE sizeof(struct evbuffer_chain)
 /** Return a pointer to extra data allocated along with an evbuffer. */
 #define EVBUFFER_CHAIN_EXTRA(t, c) (t *)((struct evbuffer_chain *)(c) + 1)

include/event2/buffer.h

@@ -437,6 +437,22 @@ char *evbuffer_readln(struct evbuffer *buffer, size_t *n_read_out,
  */
 int evbuffer_add_buffer(struct evbuffer *outbuf, struct evbuffer *inbuf);
 
+/**
+  Copy data from one evbuffer into another evbuffer.
+  
+  This is a non-destructive add.  The data from one buffer is copied
+  into the other buffer.  However, no unnecessary memory copies occur.
+  
+  Note that buffers already containing buffer references can't be added
+  to other buffers.
+  
+  @param outbuf the output buffer
+  @param inbuf the input buffer
+  @return 0 if successful, or -1 if an error occurred
+ */
+int evbuffer_add_buffer_reference(struct evbuffer *outbuf,
+    struct evbuffer *inbuf);
+
 /**
    A cleanup function for a piece of memory added to an evbuffer by
    reference.

test/regress_buffer.c

@@ -1596,6 +1596,111 @@ end:
 		evbuffer_free(buf2);
 }
 
+static void
+test_evbuffer_multicast(void *ptr)
+{
+	const char chunk1[] = "If you have found the answer to such a problem";
+	const char chunk2[] = "you ought to write it up for publication";
+			  /* -- Knuth's "Notes on the Exercises" from TAOCP */
+	char tmp[16];
+	size_t len1 = strlen(chunk1), len2=strlen(chunk2);
+
+	struct evbuffer *buf1 = NULL, *buf2 = NULL;
+
+	buf1 = evbuffer_new();
+	tt_assert(buf1);
+
+	evbuffer_add(buf1, chunk1, len1);
+	evbuffer_add(buf1, ", ", 2);
+	evbuffer_add(buf1, chunk2, len2);
+	tt_int_op(evbuffer_get_length(buf1), ==, len1+len2+2);
+
+	buf2 = evbuffer_new();
+	tt_assert(buf2);
+
+    tt_int_op(evbuffer_add_buffer_reference(buf2, buf1), ==, 0);
+    // nested references are not allowed
+    tt_int_op(evbuffer_add_buffer_reference(buf2, buf2), ==, -1);
+    tt_int_op(evbuffer_add_buffer_reference(buf1, buf2), ==, -1);
+
+    // both buffers contain the same amount of data
+    tt_int_op(evbuffer_get_length(buf1), ==, evbuffer_get_length(buf1));
+
+	/* Make sure we can drain a little from the first buffer. */
+	tt_int_op(evbuffer_remove(buf1, tmp, 6), ==, 6);
+	tt_int_op(memcmp(tmp, "If you", 6), ==, 0);
+	tt_int_op(evbuffer_remove(buf1, tmp, 5), ==, 5);
+	tt_int_op(memcmp(tmp, " have", 5), ==, 0);
+
+	/* Make sure that prepending does not meddle with immutable data */
+	tt_int_op(evbuffer_prepend(buf1, "I have ", 7), ==, 0);
+	tt_int_op(memcmp(chunk1, "If you", 6), ==, 0);
+	evbuffer_validate(buf1);
+
+	/* Make sure we can drain a little from the second buffer. */
+	tt_int_op(evbuffer_remove(buf2, tmp, 6), ==, 6);
+	tt_int_op(memcmp(tmp, "If you", 6), ==, 0);
+	tt_int_op(evbuffer_remove(buf2, tmp, 5), ==, 5);
+	tt_int_op(memcmp(tmp, " have", 5), ==, 0);
+
+	/* Make sure that prepending does not meddle with immutable data */
+	tt_int_op(evbuffer_prepend(buf2, "I have ", 7), ==, 0);
+	tt_int_op(memcmp(chunk1, "If you", 6), ==, 0);
+	evbuffer_validate(buf2);
+
+    /* Make sure the data can be read from the second buffer when the first is freed */
+	evbuffer_free(buf1);
+	buf1 = NULL;
+    
+	tt_int_op(evbuffer_remove(buf2, tmp, 6), ==, 6);
+	tt_int_op(memcmp(tmp, "I have", 6), ==, 0);
+
+	tt_int_op(evbuffer_remove(buf2, tmp, 6), ==, 6);
+	tt_int_op(memcmp(tmp, "  foun", 6), ==, 0);
+
+end:
+	if (buf1)
+		evbuffer_free(buf1);
+	if (buf2)
+		evbuffer_free(buf2);
+}
+
+static void
+test_evbuffer_multicast_drain(void *ptr)
+{
+	const char chunk1[] = "If you have found the answer to such a problem";
+	const char chunk2[] = "you ought to write it up for publication";
+			  /* -- Knuth's "Notes on the Exercises" from TAOCP */
+	size_t len1 = strlen(chunk1), len2=strlen(chunk2);
+
+	struct evbuffer *buf1 = NULL, *buf2 = NULL;
+
+	buf1 = evbuffer_new();
+	tt_assert(buf1);
+
+	evbuffer_add(buf1, chunk1, len1);
+	evbuffer_add(buf1, ", ", 2);
+	evbuffer_add(buf1, chunk2, len2);
+	tt_int_op(evbuffer_get_length(buf1), ==, len1+len2+2);
+
+	buf2 = evbuffer_new();
+	tt_assert(buf2);
+
+    tt_int_op(evbuffer_add_buffer_reference(buf2, buf1), ==, 0);
+	tt_int_op(evbuffer_get_length(buf2), ==, len1+len2+2);
+    tt_int_op(evbuffer_drain(buf1, evbuffer_get_length(buf1)), ==, 0);
+	tt_int_op(evbuffer_get_length(buf2), ==, len1+len2+2);
+    tt_int_op(evbuffer_drain(buf2, evbuffer_get_length(buf2)), ==, 0);
+	evbuffer_validate(buf1);
+	evbuffer_validate(buf2);
+
+end:
+	if (buf1)
+		evbuffer_free(buf1);
+	if (buf2)
+		evbuffer_free(buf2);
+}
+
 /* Some cases that we didn't get in test_evbuffer() above, for more coverage. */
 static void
 test_evbuffer_prepend(void *ptr)
@@ -2012,6 +2117,8 @@ struct testcase_t evbuffer_testcases[] = {
 	{ "search", test_evbuffer_search, 0, NULL, NULL },
 	{ "callbacks", test_evbuffer_callbacks, 0, NULL, NULL },
 	{ "add_reference", test_evbuffer_add_reference, 0, NULL, NULL },
+	{ "multicast", test_evbuffer_multicast, 0, NULL, NULL },
+	{ "multicast_drain", test_evbuffer_multicast_drain, 0, NULL, NULL },
 	{ "prepend", test_evbuffer_prepend, TT_FORK, NULL, NULL },
 	{ "peek", test_evbuffer_peek, 0, NULL, NULL },
 	{ "freeze_start", test_evbuffer_freeze, 0, &nil_setup, (void*)"start" },