documentation in zmq.h improved

3 files changed, 208 insertions, 116 deletions

diff --git a/bindings/c/zmq.h b/bindings/c/zmq.h
index 797d060..b65a771 100644
--- a/bindings/c/zmq.h
+++ b/bindings/c/zmq.h
@@ -26,83 +26,35 @@ extern "C" {
 
 #include <stddef.h>
 
+//  Microsoft Visual Studio uses non-standard way to export/import symbols.
 #if defined ZMQ_BUILDING_LIBZMQ_WITH_MSVC
 #define ZMQ_EXPORT __declspec(dllexport)
+#elif defined _MSC_VER
+#define ZMQ_EXPORT __declspec(dllimport)
 #else
 #define ZMQ_EXPORT
 #endif
 
+////////////////////////////////////////////////////////////////////////////////
+//  0MQ message definition.
+////////////////////////////////////////////////////////////////////////////////
+
 //  Maximal size of "Very Small Message". VSMs are passed by value
 //  to avoid excessive memory allocation/deallocation.
 //  If VMSs larger than 255 bytes are required, type of 'vsm_size'
 //  field in zmq_msg_t structure should be modified accordingly.
 #define ZMQ_MAX_VSM_SIZE 30
 
-//  Message & notification types.
-#define ZMQ_GAP 1
+//  Message types. These integers may be stored in 'content' member of the
+//  message instead of regular pointer to the data.
 #define ZMQ_DELIMITER 31
 #define ZMQ_VSM 32
 
-//  Socket options.
-#define ZMQ_HWM 1                  //  int64_t
-#define ZMQ_LWM 2                  //  int64_t
-#define ZMQ_SWAP 3                 //  int64_t
-#define ZMQ_AFFINITY 4             //  int64_t
-#define ZMQ_IDENTITY 5             //  string
-#define ZMQ_SUBSCRIBE 6            //  string
-#define ZMQ_UNSUBSCRIBE 7          //  string
-#define ZMQ_RATE 8                 //  int64_t
-#define ZMQ_RECOVERY_IVL 9         //  int64_t
-#define ZMQ_MCAST_LOOP 10          //  int64_t
-
-//  The operation should be performed in non-blocking mode. I.e. if it cannot
-//  be processed immediately, error should be returned with errno set to EAGAIN.
-#define ZMQ_NOBLOCK 1
-
-//  zmq_send should not flush the message downstream immediately. Instead, it
-//  should batch ZMQ_NOFLUSH messages and send them downstream only if zmq_flush
-//  is invoked. This is an optimisation for cases where several messages are
-//  sent in a single business transaction. However, the effect is measurable
-//  only in extremely high-perf scenarios (million messages a second or so).
-//  If that's not your case, use standard flushing send instead. See exchange
-//  example for illustration of ZMQ_NOFLUSH functionality.
-#define ZMQ_NOFLUSH 2
-
-//  Socket to communicate with a single peer. Allows for a singe connect or a
-//  single accept. There's no message routing or message filtering involved.
-#define ZMQ_P2P 0
-
-//  Socket to distribute data. Recv fuction is not implemented for this socket
-//  type. Messages are distributed in fanout fashion to all peers.
-#define ZMQ_PUB 1
-
-//  Socket to subscribe to distributed data. Send function is not implemented
-//  for this socket type. However, subscribe function can be used to modify the
-//  message filter.
-#define ZMQ_SUB 2
-
-//  Socket to send requests on and receive replies from. Requests are
-//  load-balanced among all the peers. This socket type doesn't allow for more
-//  recv's that there were send's.
-#define ZMQ_REQ 3
-
-//  Socket to receive requests from and send replies to. This socket type allows
-//  only an alternated sequence of recv's and send's. Each send is routed to
-//  the peer that the previous recv delivered message from.
-#define ZMQ_REP 4
-
-//  Option specifying that the sockets should be pollable. This may be a little
-//  less efficient that raw non-pollable sockets.
-#define ZMQ_POLL 1
-
-//  Prototype for the message body deallocation functions.
-//  It is deliberately defined in the way to comply with standard C free.
-typedef void (zmq_free_fn) (void *data);
-
 //  A message. If 'shared' is true, message content pointed to by 'content'
 //  is shared, i.e. reference counting is used to manage its lifetime
-//  rather than straighforward malloc/free. struct zmq_msg_content is
-//  not declared in the API.
+//  rather than straighforward malloc/free. Not that 'content' is not a pointer
+//  to the raw data. Rather it is pointer to zmq::msg_content_t structure
+//  (see src/msg_content.hpp for its definition).
 struct zmq_msg_t
 {
     void *content;
@@ -116,12 +68,15 @@ ZMQ_EXPORT int zmq_msg_init (struct zmq_msg_t *msg);
 
 //  Initialise a message 'size' bytes long.
 //
-//  Errors: ENOMEM - the size is too large to allocate.
+//  Errors: ENOMEM - message is too big to fit into memory.
 ZMQ_EXPORT int zmq_msg_init_size (struct zmq_msg_t *msg, size_t size);
 
 //  Initialise a message from an existing buffer. Message isn't copied,
-//  instead 0MQ infrastructure take ownership of the buffer and call
-//  deallocation functio (ffn) once it's not needed anymore.
+//  instead 0MQ infrastructure takes ownership of the buffer and
+//  deallocation function (ffn) will be called once the data are not
+//  needed anymore. Note that deallocation function prototype is designed
+//  so that it complies with standard C 'free' function.
+typedef void (zmq_free_fn) (void *data);
 ZMQ_EXPORT int zmq_msg_init_data (struct zmq_msg_t *msg, void *data,
     size_t size, zmq_free_fn *ffn);
 
@@ -145,35 +100,180 @@ ZMQ_EXPORT void *zmq_msg_data (struct zmq_msg_t *msg);
 //  Return size of message data (in bytes).
 ZMQ_EXPORT size_t zmq_msg_size (struct zmq_msg_t *msg);
 
-//  Returns type of the message.
-ZMQ_EXPORT int zmq_msg_type (struct zmq_msg_t *msg);
+////////////////////////////////////////////////////////////////////////////////
+//  0MQ infrastructure (a.k.a. context) initialisation & termination.
+////////////////////////////////////////////////////////////////////////////////
+
+//  Flag specifying that the sockets within this context should be pollable.
+//  This may be a little less efficient that raw non-pollable sockets.
+#define ZMQ_POLL 1
 
 //  Initialise 0MQ context. 'app_threads' specifies maximal number
-//  of application threads that can have open sockets at the same time.
+//  of application threads that can own open sockets at the same time.
 //  'io_threads' specifies the size of thread pool to handle I/O operations.
+//  'flags' argument is a bitmap composed of the flags defined above.
 //
 //  Errors: EINVAL - one of the arguments is less than zero or there are no
 //                   threads declared at all.
 ZMQ_EXPORT void *zmq_init (int app_threads, int io_threads, int flags);
 
-//  Deinitialise 0MQ context including all the open sockets. Closing
-//  sockets after zmq_term has been called will result in undefined behaviour.
+//  Deinitialise 0MQ context. If there are still open sockets, actual
+//  deinitialisation of the context is delayed till all the sockets are closed.
 ZMQ_EXPORT int zmq_term (void *context);
 
-//  Open a socket.
+////////////////////////////////////////////////////////////////////////////////
+//  0MQ socket definition.
+////////////////////////////////////////////////////////////////////////////////
+
+//  Creating a 0MQ socket.
+//  **********************
+
+//  Socket to communicate with a single peer. Allows for a singe connect or a
+//  single accept. There's no message routing or message filtering involved.
+#define ZMQ_P2P 0
+
+//  Socket to distribute data. Recv fuction is not implemented for this socket
+//  type. Messages are distributed in fanout fashion to all the peers.
+#define ZMQ_PUB 1
+
+//  Socket to subscribe for data. Send function is not implemented for this
+//  socket type. However, subscribe function can be used to modify the
+//  message filter (see ZMQ_SUBSCRIBE socket option).
+#define ZMQ_SUB 2
+
+//  Socket to send requests and receive replies. Requests are
+//  load-balanced among all the peers. This socket type allows
+//  only an alternated sequence of send's and recv's
+#define ZMQ_REQ 3
+
+//  Socket to receive requests and send replies. This socket type allows
+//  only an alternated sequence of recv's and send's. Each send is routed to
+//  the peer that issued the last received request.
+#define ZMQ_REP 4
+
+//  Open a socket. 'type' is one of the socket types defined above.
 //
 //  Errors: EINVAL - invalid socket type.
 //          EMFILE - the number of application threads entitled to hold open
 //                   sockets at the same time was exceeded.
 ZMQ_EXPORT void *zmq_socket (void *context, int type);
 
+//  Destroying the socket.
+//  **********************
+
 //  Close the socket.
 ZMQ_EXPORT int zmq_close (void *s);
 
-//  Sets an option on the socket.
-//  EINVAL - unknown option, a value with incorrect length or an invalid value.
-ZMQ_EXPORT int zmq_setsockopt (void *s, int option_, const void *optval_,
-    size_t optvallen_); 
+//  Manipulating socket options.
+//  ****************************
+
+//  Available socket options, their types and default values.
+
+//  High watermark for the message pipes associated with the socket. The water
+//  mark cannot be exceeded. If the messages don't fit into the pipe emergency
+//  mechanisms of the particular socket type are used (block, drop etc.) If HWM
+//  is set to zero, there are no limits for the content of the pipe.
+//  Type: int64_t  Unit: bytes  Default: 0
+#define ZMQ_HWM 1
+
+//  Low watermark makes sense only if high watermark is defined (is non-zero).
+//  When the emergency state is reached when messages overflow the pipe, the
+//  emergency lasts till the size of the pipe decreases to low watermark.
+//  At that point normal state is resumed.
+//  Type: int64_t  Unit: bytes  Default: 0
+#define ZMQ_LWM 2
+
+//  Swap allows the pipe to exceed high watermark. However, the data are written
+//  to the disk rather than held in the memory. While the high watermark is not
+//  exceeded there is no disk activity involved though. The value of the option
+//  defines maximal size of the swap file.
+//  Type: int64_t  Unit: bytes  Default: 0
+#define ZMQ_SWAP 3
+
+//  Affinity defines which threads in the thread pool will be used to handle
+//  newly created sockets. This way you can dedicate some of the threads (CPUs)
+//  to a specific work. Value of 0 means no affinity, work is distributed
+//  fairly among the threads in the thread pool. For non-zero values, the lowest
+//  bit corresponds to the thread 1, second lowest bit to the thread 2 etc.
+//  Thus, value of 3 means that from now on newly created sockets will handle
+//  I/O activity exclusively using threads no. 1 and 2.
+//  Type: int64_t  Unit: N/A (bitmap)  Default: 0
+#define ZMQ_AFFINITY 4
+
+//  Identity of the socket. Identity is important when restarting applications.
+//  If the socket has no identity, each run of the application is completely
+//  separated from other runs. However, with identity application reconnects to
+//  existing infrastructure left by the previous run. Thus it may receive
+//  messages that were sent in the meantime, it shares pipe limits with the
+//  previous run etc.
+//  Type: string  Unit: N/A  Default: NULL
+#define ZMQ_IDENTITY 5
+
+//  Applicable only to 'sub' socket type. Eastablishes new message filter.
+//  When 'sub' socket is created all the incoming messages are filtered out.
+//  This option allows you to subscribe for all messages ("*"), messages with
+//  specific topic ("x.y.z") and/or messages with specific topic prefix
+//  ("x.y.*"). Topic is one-byte-size-prefixed string located at
+//  the very beginning of the message. Multiple filters can be attached to
+//  a single 'sub' socket. In that case message passes if it matches at least
+//  one of the filters.
+//  Type: string  Unit: N/A  Default: N/A
+#define ZMQ_SUBSCRIBE 6
+
+//  Applicable only to 'sub' socket type. Removes existing message filter.
+//  The filter specified must match the string passed to ZMQ_SUBSCRIBE options
+//  exactly. If there were several instances of the same filter created,
+//  this options removes only one of them, leaving the rest in place
+//  and functional.
+//  Type: string  Unit: N/A  Default: N/A
+#define ZMQ_UNSUBSCRIBE 7
+
+//  This option applies only to multicast transports (pgm & udp). It specifies
+//  maximal outgoing data rate that an individual sender socket can send.
+//  Type: uint64_t  Unit: kilobits/second  Default: 100
+#define ZMQ_RATE 8
+
+//  This option applies only to multicast transports (pgm & udp). It specifies
+//  how long can the receiver socket survive when the sender is inaccessible.
+//  Keep in mind that large recovery intervals at high data rates result in
+//  very large recovery buffers, meaning that you can easily overload your box
+//  by setting say 1 minute recovery interval at 1Gb/s rate (requires
+//  7GB in-memory buffer).
+//  Type: uint64_t Unit: seconds Default: 10 
+#define ZMQ_RECOVERY_IVL 9
+
+//  This option applies only to multicast transports (pgm & udp). Value of 1
+//  means that the mutlicast packets can be received on the box they were sent
+//  from. Setting the value to 0 disables the loopback functionality which
+//  can have negative impact on the performance. if possible, disable
+//  the loopback in production environments.
+//  Type: uint64_t Unit: N/A (boolean value) Default: 1
+#define ZMQ_MCAST_LOOP 10
+
+//  Sets an option on the socket. 'option' argument specifies the option (see
+//  the option list above). 'optval' is a pointer to the value to set,
+//  'optvallen' is the size of the value in bytes.
+//
+//  Errors: EINVAL - unknown option, a value with incorrect length
+//                   or invalid value.
+ZMQ_EXPORT int zmq_setsockopt (void *s, int option, const void *optval,
+    size_t optvallen); 
+
+//  Creating connections.
+//  *********************
+
+//  Addresses are composed of the name of the protocol to use followed by ://
+//  and a protocol-specific address. Available protocols:
+//
+//  tcp - the address is composed of IP address and port delimited by colon
+//        sign (:). The IP address can be a hostname (with 'connect') or
+//        a network interface name (with 'bind'). Examples "tcp://eth0:5555",
+//        "tcp://192.168.0.1:20000", "tcp://hq.mycompany.com:80".
+//
+//  pgm & udp - both protocols have same address format. It's network interface
+//              to use, semicolon (;), multicast group IP address, colon (:) and
+//              port. Examples: "pgm://eth2;224.0.0.1:8000",
+//              "udp://192.168.0.111;224.1.1.1:5555".
 
 //  Bind the socket to a particular address.
 ZMQ_EXPORT int zmq_bind (void *s, const char *addr);
@@ -181,12 +281,25 @@ ZMQ_EXPORT int zmq_bind (void *s, const char *addr);
 //  Connect the socket to a particular address.
 ZMQ_EXPORT int zmq_connect (void *s, const char *addr);
 
+//  Sending and receiving messages.
+//  *******************************
+
+//  The flag specifying that the operation should be performed in
+//  non-blocking mode. I.e. if it cannot be processed immediately,
+//  error should be returned with errno set to EAGAIN.
+#define ZMQ_NOBLOCK 1
+
+//  The flag specifying that zmq_send should not flush the message downstream
+//  immediately. Instead, it should batch ZMQ_NOFLUSH messages and send them
+//  downstream only if zmq_flush is invoked. This is an optimisation for cases
+//  where several messages are sent in a single business transaction. However,
+//  the effect is measurable only in extremely high-perf scenarios
+//  (million messages a second or so). If that's not your case, use standard
+//  flushing send instead.
+#define ZMQ_NOFLUSH 2
+
 //  Send the message 'msg' to the socket 's'. 'flags' argument can be
-//  combination of following values:
-//  ZMQ_NOBLOCK - if message cannot be sent, return immediately.
-//  ZMQ_NOFLUSH - message won't be sent immediately. It'll be sent with either
-//                subsequent flushing send or explicit call to zmq_flush
-//                function.
+//  combination the flags described above.
 //
 //  Errors: EAGAIN - message cannot be sent at the moment (applies only to
 //                   non-blocking send).
@@ -199,18 +312,28 @@ ZMQ_EXPORT int zmq_send (void *s, struct zmq_msg_t *msg, int flags);
 ZMQ_EXPORT int zmq_flush (void *s);
 
 //  Send a message from the socket 's'. 'flags' argument can be combination
-//  of following values:
-//  ZMQ_NOBLOCK - if message cannot be received, return immediately.
+//  of the flags described above.
 //
 //  Errors: EAGAIN - message cannot be received at the moment (applies only to
 //                   non-blocking receive).
 //          EFAULT - function isn't supported by particular socket type.
 ZMQ_EXPORT int zmq_recv (void *s, struct zmq_msg_t *msg, int flags);
 
+////////////////////////////////////////////////////////////////////////////////
+//  Helper functions.
+////////////////////////////////////////////////////////////////////////////////
+
 //  Helper functions used by perf tests so that they don't have to care
 //  about minutiae of time-related functions on different OS platforms.
+
+//  Starts the stopwatch. Returns the handle to the watch.
 ZMQ_EXPORT void *zmq_stopwatch_start ();
+
+//  Stops the stopwatch. Returns the number of microseconds elapsed since
+//  the stopwatch was started.
 ZMQ_EXPORT unsigned long zmq_stopwatch_stop (void *watch_);
+
+//  Sleeps for specified number of seconds.
 ZMQ_EXPORT void zmq_sleep (int seconds_);
 
 #ifdef __cplusplus
diff --git a/bindings/cpp/zmq.hpp b/bindings/cpp/zmq.hpp
index a9e63b5..cf7d347 100644
--- a/bindings/cpp/zmq.hpp
+++ b/bindings/cpp/zmq.hpp
@@ -32,13 +32,6 @@ namespace zmq
 
     typedef zmq_free_fn free_fn;
 
-    enum message_type_t
-    {
-        message_data = 1 << 0,
-        message_gap = 1 << ZMQ_GAP,
-        message_delimiter = 1 << ZMQ_DELIMITER
-    };
-
     //  The class masquerades POSIX-style errno error as a C++ exception.
     class error_t : public std::exception
     {
@@ -148,12 +141,6 @@ namespace zmq
                 throw error_t ();
         }
 
-        //  Returns message type.
-        inline message_type_t type ()
-        {
-            return (message_type_t) (1 << zmq_msg_type (this));
-        }
-
         //  Returns pointer to message's data buffer.
         inline void *data ()
         {
diff --git a/src/zmq.cpp b/src/zmq.cpp
index 36f30eb..e831046 100644
--- a/src/zmq.cpp
+++ b/src/zmq.cpp
@@ -84,8 +84,7 @@ int zmq_msg_close (zmq_msg_t *msg_)
 {
     //  For VSMs and delimiters there are no resources to free.
     if (msg_->content == (zmq::msg_content_t*) ZMQ_DELIMITER ||
-          msg_->content == (zmq::msg_content_t*) ZMQ_VSM ||
-          msg_->content == (zmq::msg_content_t*) ZMQ_GAP)
+          msg_->content == (zmq::msg_content_t*) ZMQ_VSM)
         return 0;
 
     //  If the content is not shared, or if it is shared and the reference.
@@ -118,10 +117,8 @@ int zmq_msg_copy (zmq_msg_t *dest_, zmq_msg_t *src_)
     zmq_msg_close (dest_);
 
     //  VSMs and delimiters require no special handling.
-    if (src_->content !=
-          (zmq::msg_content_t*) ZMQ_DELIMITER &&
-          src_->content != (zmq::msg_content_t*) ZMQ_VSM &&
-          src_->content != (zmq::msg_content_t*) ZMQ_GAP) {
+    if (src_->content != (zmq::msg_content_t*) ZMQ_DELIMITER &&
+          src_->content != (zmq::msg_content_t*) ZMQ_VSM) {
 
         //  One reference is added to shared messages. Non-shared messages
         //  are turned into shared messages and reference count is set to 2.
@@ -142,9 +139,7 @@ void *zmq_msg_data (zmq_msg_t *msg_)
 {
     if (msg_->content == (zmq::msg_content_t*) ZMQ_VSM)
         return msg_->vsm_data;
-    if (msg_->content ==
-          (zmq::msg_content_t*) ZMQ_DELIMITER ||
-          msg_->content == (zmq::msg_content_t*) ZMQ_GAP)
+    if (msg_->content == (zmq::msg_content_t*) ZMQ_DELIMITER)
         return NULL;
 
     return ((zmq::msg_content_t*) msg_->content)->data;
@@ -154,25 +149,12 @@ size_t zmq_msg_size (zmq_msg_t *msg_)
 {
     if (msg_->content == (zmq::msg_content_t*) ZMQ_VSM)
         return msg_->vsm_size;
-    if (msg_->content ==
-          (zmq::msg_content_t*) ZMQ_DELIMITER ||
-          msg_->content == (zmq::msg_content_t*) ZMQ_GAP)
+    if (msg_->content == (zmq::msg_content_t*) ZMQ_DELIMITER)
         return 0;
 
     return ((zmq::msg_content_t*) msg_->content)->size;
 }
 
-int zmq_msg_type (zmq_msg_t *msg_)
-{
-    //  If it's a genuine message, return 0.
-    if (msg_->content >= (zmq::msg_content_t*) ZMQ_VSM)
-            return 0;
-
-    //   Trick the compiler to believe that content is an integer.
-    unsigned char *offset = 0;
-    return (((const unsigned char*) msg_->content) - offset);
-}
-
 void *zmq_init (int app_threads_, int io_threads_, int flags_)
 {
     //  There should be at least a single thread managed by the dispatcher.