Problem: enormous memory increase due to zero copy decoding

The zero copy decoding strategy implemented for 4.2.0 can lead to a large
increase of main memory usage in some cases (I have seen one program go up to
40G from 10G after upgrading from 4.1.4). This commit adds a new option to
contexts, called ZMQ_ZERO_COPY_RECV, which allows one to switch to the old
decoding strategy.

doc/zmq_ctx_get.txt

@@ -39,6 +39,12 @@ The 'ZMQ_MAX_MSGSZ' argument returns the maximum size of a message
 allowed for this context. Default value is INT_MAX.
 
 
+ZMQ_ZERO_COPY_RCV: Get message decoding strategy
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_ZERO_COPY_RCV' argument return whether message decoder uses a zero copy
+strategy when receiving messages. Default value is 1.
+
+
 ZMQ_SOCKET_LIMIT: Get largest configurable number of sockets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_SOCKET_LIMIT' argument returns the largest number of sockets that

doc/zmq_ctx_set.txt

@@ -127,6 +127,18 @@ Default value:: INT_MAX
 Maximum value:: INT_MAX
 
 
+ZMQ_ZERO_COPY_RCV: Specify message decoding strategy
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_ZERO_COPY_RCV' argument specifies whether the message decoder should
+use a zero copy strategy when receiving messages. The zero copy strategy can
+lead to increased memory usage in some cases. This option allows you to use the
+older copying strategy. You can query the value of this option with
+linkzmq:zmq_ctx_get[3] using the 'ZMQ_ZERO_COPY_RECV' option.
+
+[horizontal]
+Default value:: 1
+
+
 ZMQ_MAX_SOCKETS: Set maximum number of sockets
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_MAX_SOCKETS' argument sets the maximum number of sockets allowed

include/zmq.h

@@ -628,6 +628,7 @@ ZMQ_EXPORT void zmq_threadclose (void *thread);
 #define ZMQ_THREAD_AFFINITY_CPU_ADD 7
 #define ZMQ_THREAD_AFFINITY_CPU_REMOVE 8
 #define ZMQ_THREAD_NAME_PREFIX 9
+#define ZMQ_ZERO_COPY_RECV 10
 
 /*  DRAFT Socket methods.                                                     */
 ZMQ_EXPORT int zmq_join (void *s, const char *group);

src/ctx.cpp

@@ -76,7 +76,8 @@ zmq::ctx_t::ctx_t () :
     max_msgsz (INT_MAX),
     io_thread_count (ZMQ_IO_THREADS_DFLT),
     blocky (true),
-    ipv6 (false)
+    ipv6 (false),
+    zero_copy (true)
 {
 #ifdef HAVE_FORK
     pid = getpid ();
@@ -245,6 +246,9 @@ int zmq::ctx_t::set (int option_, int optval_)
     } else if (option_ == ZMQ_MAX_MSGSZ && optval_ >= 0) {
         scoped_lock_t locker (opt_sync);
         max_msgsz = optval_ < INT_MAX ? optval_ : INT_MAX;
+    } else if (option_ == ZMQ_ZERO_COPY_RECV && optval_ >= 0) {
+        scoped_lock_t locker (opt_sync);
+        zero_copy = (optval_ != 0);
     } else {
         rc = thread_ctx_t::set (option_, optval_);
     }
@@ -268,7 +272,9 @@ int zmq::ctx_t::get (int option_)
         rc = max_msgsz;
     else if (option_ == ZMQ_MSG_T_SIZE)
         rc = sizeof (zmq_msg_t);
-    else {
+    else if (option_ == ZMQ_ZERO_COPY_RECV) {
+        rc = zero_copy;
+    } else {
         errno = EINVAL;
         rc = -1;
     }

src/ctx.hpp

@@ -234,6 +234,9 @@ class ctx_t : public thread_ctx_t
     //  Is IPv6 enabled on this context?
     bool ipv6;
 
+    // Should we use zero copy message decoding in this context?
+    bool zero_copy;
+
     ctx_t (const ctx_t &);
     const ctx_t &operator= (const ctx_t &);
 

src/norm_engine.cpp

@@ -405,8 +405,8 @@ void zmq::norm_engine_t::recv_data (NormObjectHandle object)
           (NormRxStreamState *) NormObjectGetUserData (object);
         if (NULL == rxState) {
             // This is a new stream, so create rxState with zmq decoder, etc
-            rxState =
-              new (std::nothrow) NormRxStreamState (object, options.maxmsgsize);
+            rxState = new (std::nothrow)
+              NormRxStreamState (object, options.maxmsgsize, options.zero_copy);
             errno_assert (rxState);
 
             if (!rxState->Init ()) {
@@ -547,9 +547,10 @@ void zmq::norm_engine_t::recv_data (NormObjectHandle object)
 } // end zmq::norm_engine_t::recv_data()
 
 zmq::norm_engine_t::NormRxStreamState::NormRxStreamState (
-  NormObjectHandle normStream, int64_t maxMsgSize) :
+  NormObjectHandle normStream, int64_t maxMsgSize, bool zeroCopy) :
     norm_stream (normStream),
     max_msg_size (maxMsgSize),
+    zero_copy (zeroCopy),
     in_sync (false),
     rx_ready (false),
     zmq_decoder (NULL),
@@ -582,7 +583,8 @@ bool zmq::norm_engine_t::NormRxStreamState::Init ()
     if (NULL != zmq_decoder)
         delete zmq_decoder;
     // Note "in_batch_size" comes from config.h
-    zmq_decoder = new (std::nothrow) v2_decoder_t (in_batch_size, max_msg_size);
+    zmq_decoder =
+      new (std::nothrow) v2_decoder_t (in_batch_size, max_msg_size, zero_copy);
     alloc_assert (zmq_decoder);
     if (NULL != zmq_decoder) {
         buffer_count = 0;

src/norm_engine.hpp

@@ -68,7 +68,9 @@ class norm_engine_t : public io_object_t, public i_engine
     class NormRxStreamState
     {
       public:
-        NormRxStreamState (NormObjectHandle normStream, int64_t maxMsgSize);
+        NormRxStreamState (NormObjectHandle normStream,
+                           int64_t maxMsgSize,
+                           bool zeroCopy);
         ~NormRxStreamState ();
 
         NormObjectHandle GetStreamHandle () const { return norm_stream; }
@@ -132,6 +134,7 @@ class norm_engine_t : public io_object_t, public i_engine
       private:
         NormObjectHandle norm_stream;
         int64_t max_msg_size;
+        bool zero_copy;
         bool in_sync;
         bool rx_ready;
         v2_decoder_t *zmq_decoder;

src/options.cpp

@@ -91,7 +91,8 @@ zmq::options_t::options_t () :
     heartbeat_timeout (-1),
     use_fd (-1),
     zap_enforce_domain (false),
-    loopback_fastpath (false)
+    loopback_fastpath (false),
+    zero_copy (true)
 {
     memset (curve_public_key, 0, CURVE_KEYSIZE);
     memset (curve_secret_key, 0, CURVE_KEYSIZE);

src/options.hpp

@@ -251,6 +251,9 @@ struct options_t
 
     // Use of loopback fastpath.
     bool loopback_fastpath;
+
+    // Use zero copy strategy for storing message content when decoding.
+    bool zero_copy;
 };
 }
 

src/socket_base.cpp

@@ -206,6 +206,7 @@ zmq::socket_base_t::socket_base_t (ctx_t *parent_,
     options.socket_id = sid_;
     options.ipv6 = (parent_->get (ZMQ_IPV6) != 0);
     options.linger.store (parent_->get (ZMQ_BLOCKY) ? -1 : 0);
+    options.zero_copy = parent_->get (ZMQ_ZERO_COPY_RECV);
 
     if (thread_safe) {
         mailbox = new (std::nothrow) mailbox_safe_t (&sync);

src/stream_engine.cpp

@@ -636,15 +636,15 @@ bool zmq::stream_engine_t::handshake ()
         encoder = new (std::nothrow) v2_encoder_t (out_batch_size);
         alloc_assert (encoder);
 
-        decoder =
-          new (std::nothrow) v2_decoder_t (in_batch_size, options.maxmsgsize);
+        decoder = new (std::nothrow)
+          v2_decoder_t (in_batch_size, options.maxmsgsize, options.zero_copy);
         alloc_assert (decoder);
     } else {
         encoder = new (std::nothrow) v2_encoder_t (out_batch_size);
         alloc_assert (encoder);
 
-        decoder =
-          new (std::nothrow) v2_decoder_t (in_batch_size, options.maxmsgsize);
+        decoder = new (std::nothrow)
+          v2_decoder_t (in_batch_size, options.maxmsgsize, options.zero_copy);
         alloc_assert (decoder);
 
         if (options.mechanism == ZMQ_NULL

src/v2_decoder.cpp

@@ -38,10 +38,13 @@
 #include "wire.hpp"
 #include "err.hpp"
 
-zmq::v2_decoder_t::v2_decoder_t (size_t bufsize_, int64_t maxmsgsize_) :
+zmq::v2_decoder_t::v2_decoder_t (size_t bufsize_,
+                                 int64_t maxmsgsize_,
+                                 bool zero_copy_) :
     shared_message_memory_allocator (bufsize_),
     decoder_base_t<v2_decoder_t, shared_message_memory_allocator> (this),
     msg_flags (0),
+    zero_copy (zero_copy_),
     maxmsgsize (maxmsgsize_)
 {
     int rc = in_progress.init ();
@@ -111,8 +114,9 @@ int zmq::v2_decoder_t::size_ready (uint64_t msg_size,
     // the current message can exceed the current buffer. We have to copy the buffer
     // data into a new message and complete it in the next receive.
 
-    if (unlikely ((unsigned char *) read_pos + msg_size
-                  > (data () + size ()))) {
+    if (unlikely (
+          !zero_copy
+          || ((unsigned char *) read_pos + msg_size > (data () + size ())))) {
         // a new message has started, but the size would exceed the pre-allocated arena
         // this happens every time when a message does not fit completely into the buffer
         rc = in_progress.init_size (static_cast<size_t> (msg_size));

src/v2_decoder.hpp

@@ -44,7 +44,7 @@ class v2_decoder_t :
   public decoder_base_t<v2_decoder_t, shared_message_memory_allocator>
 {
   public:
-    v2_decoder_t (size_t bufsize_, int64_t maxmsgsize_);
+    v2_decoder_t (size_t bufsize_, int64_t maxmsgsize_, bool zero_copy_);
     virtual ~v2_decoder_t ();
 
     //  i_decoder interface.
@@ -62,6 +62,7 @@ class v2_decoder_t :
     unsigned char msg_flags;
     msg_t in_progress;
 
+    const bool zero_copy;
     const int64_t maxmsgsize;
 
     v2_decoder_t (const v2_decoder_t &);

src/zmq_draft.h

@@ -99,6 +99,7 @@ unsigned long zmq_stopwatch_intermediate (void *watch_);
 #define ZMQ_THREAD_AFFINITY_CPU_ADD 7
 #define ZMQ_THREAD_AFFINITY_CPU_REMOVE 8
 #define ZMQ_THREAD_NAME_PREFIX 9
+#define ZMQ_ZERO_COPY_RECV 10
 
 /*  DRAFT Socket methods.                                                     */
 int zmq_join (void *s, const char *group);

tests/test_ctx_options.cpp

@@ -146,6 +146,56 @@ void test_ctx_thread_opts (void *ctx)
 #endif
 }
 
+void test_ctx_zero_copy (void *ctx)
+{
+#ifdef ZMQ_ZERO_COPY_RECV
+    int zero_copy;
+    // Default value is 1.
+    zero_copy = zmq_ctx_get (ctx, ZMQ_ZERO_COPY_RECV);
+    assert (zero_copy == 1);
+
+    // Test we can set it to 0.
+    assert (0 == zmq_ctx_set (ctx, ZMQ_ZERO_COPY_RECV, 0));
+    zero_copy = zmq_ctx_get (ctx, ZMQ_ZERO_COPY_RECV);
+    assert (zero_copy == 0);
+
+    // Create a TCP socket pair using the context and test that messages can be
+    // received. Note that inproc sockets cannot be used for this test.
+    void *pull = zmq_socket (ctx, ZMQ_PULL);
+    assert (0 == zmq_bind (pull, "tcp://127.0.0.1:*"));
+
+    void *push = zmq_socket (ctx, ZMQ_PUSH);
+    size_t endpoint_len = MAX_SOCKET_STRING;
+    char endpoint[MAX_SOCKET_STRING];
+    assert (
+      0 == zmq_getsockopt (pull, ZMQ_LAST_ENDPOINT, endpoint, &endpoint_len));
+    assert (0 == zmq_connect (push, endpoint));
+
+    const char *small_str = "abcd";
+    const char *large_str =
+      "01234567890123456789012345678901234567890123456789";
+
+    assert (4 == zmq_send (push, (void *) small_str, 4, 0));
+    assert (40 == zmq_send (push, (void *) large_str, 40, 0));
+
+    zmq_msg_t small_msg, large_msg;
+    zmq_msg_init (&small_msg);
+    zmq_msg_init (&large_msg);
+    assert (4 == zmq_msg_recv (&small_msg, pull, 0));
+    assert (40 == zmq_msg_recv (&large_msg, pull, 0));
+    assert (!strncmp (small_str, (const char *) zmq_msg_data (&small_msg), 4));
+    assert (!strncmp (large_str, (const char *) zmq_msg_data (&large_msg), 40));
+
+    // Clean up.
+    assert (0 == zmq_close (push));
+    assert (0 == zmq_close (pull));
+    assert (0 == zmq_msg_close (&small_msg));
+    assert (0 == zmq_msg_close (&large_msg));
+    assert (0 == zmq_ctx_set (ctx, ZMQ_ZERO_COPY_RECV, 1));
+    zero_copy = zmq_ctx_get (ctx, ZMQ_ZERO_COPY_RECV);
+    assert (zero_copy == 1);
+#endif
+}
 
 int main (void)
 {
@@ -173,6 +223,7 @@ int main (void)
     assert (zmq_ctx_get (ctx, ZMQ_IPV6) == 1);
 
     test_ctx_thread_opts (ctx);
+    test_ctx_zero_copy (ctx);
 
     void *router = zmq_socket (ctx, ZMQ_ROUTER);
     int value;

tests/testutil.hpp

@@ -43,7 +43,7 @@
 //  settled. Tested to work reliably at 1 msec on a fast PC.
 #define SETTLE_TIME 300 //  In msec
 //  Commonly used buffer size for ZMQ_LAST_ENDPOINT
-#define MAX_SOCKET_STRING sizeof ("tcp://127.0.0.1:65536")
+#define MAX_SOCKET_STRING sizeof ("tcp://[::ffff:127.127.127.127]:65536")
 
 //  We need to test codepaths with non-random bind ports. List them here to
 //  keep them unique, to allow parallel test runs.