Multiple pipelines and limiting the number of connections.

Introducing a number of options to the multi interface that
allows for multiple pipelines to the same host, in order to
optimize the balance between the penalty for opening new
connections and the potential pipelining latency.

Two new options for limiting the number of connections:

CURLMOPT_MAX_HOST_CONNECTIONS - Limits the number of running connections
to the same host. When adding a handle that exceeds this limit,
that handle will be put in a pending state until another handle is
finished, so we can reuse the connection.

CURLMOPT_MAX_TOTAL_CONNECTIONS - Limits the number of connections in total.
When adding a handle that exceeds this limit,
that handle will be put in a pending state until another handle is
finished. The free connection will then be reused, if possible, or
closed if the pending handle can't reuse it.

Several new options for pipelining:

CURLMOPT_MAX_PIPELINE_LENGTH - Limits the pipeling length. If a
pipeline is "full" when a connection is to be reused, a new connection
will be opened if the CURLMOPT_MAX_xxx_CONNECTIONS limits allow it.
If not, the handle will be put in a pending state until a connection is
ready (either free or a pipe got shorter).

CURLMOPT_CONTENT_LENGTH_PENALTY_SIZE - A pipelined connection will not
be reused if it is currently processing a transfer with a content
length that is larger than this.

CURLMOPT_CHUNK_LENGTH_PENALTY_SIZE - A pipelined connection will not
be reused if it is currently processing a chunk larger than this.

CURLMOPT_PIPELINING_SITE_BL - A blacklist of hosts that don't allow
pipelining.

CURLMOPT_PIPELINING_SERVER_BL - A blacklist of server types that don't allow
pipelining.

See the curl_multi_setopt() man page for details.

1 files changed, 44 insertions, 19 deletions

diff --git a/lib/multihandle.h b/lib/multihandle.h
index 941835941..3fcd9c0e6 100644
--- a/lib/multihandle.h
+++ b/lib/multihandle.h
@@ -31,25 +31,26 @@ struct Curl_message {
    well!
 */
 typedef enum {
-  CURLM_STATE_INIT,        /* 0 - start in this state */
-  CURLM_STATE_CONNECT,     /* 1 - resolve/connect has been sent off */
-  CURLM_STATE_WAITRESOLVE, /* 2 - awaiting the resolve to finalize */
-  CURLM_STATE_WAITCONNECT, /* 3 - awaiting the connect to finalize */
-  CURLM_STATE_WAITPROXYCONNECT, /* 4 - awaiting proxy CONNECT to finalize */
-  CURLM_STATE_PROTOCONNECT, /* 5 - completing the protocol-specific connect
-                               phase */
-  CURLM_STATE_WAITDO,      /* 6 - wait for our turn to send the request */
-  CURLM_STATE_DO,          /* 7 - start send off the request (part 1) */
-  CURLM_STATE_DOING,       /* 8 - sending off the request (part 1) */
-  CURLM_STATE_DO_MORE,     /* 9 - send off the request (part 2) */
-  CURLM_STATE_DO_DONE,     /* 10 - done sending off request */
-  CURLM_STATE_WAITPERFORM, /* 11 - wait for our turn to read the response */
-  CURLM_STATE_PERFORM,     /* 12 - transfer data */
-  CURLM_STATE_TOOFAST,     /* 13 - wait because limit-rate exceeded */
-  CURLM_STATE_DONE,        /* 14 - post data transfer operation */
-  CURLM_STATE_COMPLETED,   /* 15 - operation complete */
-  CURLM_STATE_MSGSENT,     /* 16 - the operation complete message is sent */
-  CURLM_STATE_LAST         /* 17 - not a true state, never use this */
+  CURLM_STATE_INIT,         /* 0 - start in this state */
+  CURLM_STATE_CONNECT_PEND, /* 1 - no connections, waiting for one */
+  CURLM_STATE_CONNECT,      /* 2 - resolve/connect has been sent off */
+  CURLM_STATE_WAITRESOLVE,  /* 3 - awaiting the resolve to finalize */
+  CURLM_STATE_WAITCONNECT,  /* 4 - awaiting the connect to finalize */
+  CURLM_STATE_WAITPROXYCONNECT, /* 5 - awaiting proxy CONNECT to finalize */
+  CURLM_STATE_PROTOCONNECT, /* 6 - completing the protocol-specific connect
+                                   phase */
+  CURLM_STATE_WAITDO,       /* 7 - wait for our turn to send the request */
+  CURLM_STATE_DO,           /* 8 - start send off the request (part 1) */
+  CURLM_STATE_DOING,        /* 9 - sending off the request (part 1) */
+  CURLM_STATE_DO_MORE,      /* 10 - send off the request (part 2) */
+  CURLM_STATE_DO_DONE,      /* 11 - done sending off request */
+  CURLM_STATE_WAITPERFORM,  /* 12 - wait for our turn to read the response */
+  CURLM_STATE_PERFORM,      /* 13 - transfer data */
+  CURLM_STATE_TOOFAST,      /* 14 - wait because limit-rate exceeded */
+  CURLM_STATE_DONE,         /* 15 - post data transfer operation */
+  CURLM_STATE_COMPLETED,    /* 16 - operation complete */
+  CURLM_STATE_MSGSENT,      /* 17 - the operation complete message is sent */
+  CURLM_STATE_LAST          /* 18 - not a true state, never use this */
 } CURLMstate;
 
 /* we support N sockets per easy handle. Set the corresponding bit to what
@@ -123,6 +124,30 @@ struct Curl_multi {
   long maxconnects; /* if >0, a fixed limit of the maximum number of entries
                        we're allowed to grow the connection cache to */
 
+  long max_host_connections; /* if >0, a fixed limit of the maximum number
+                                of connections per host */
+
+  long max_total_connections; /* if >0, a fixed limit of the maximum number
+                                 of connections in total */
+
+  long max_pipeline_length; /* if >0, maximum number of requests in a
+                               pipeline */
+
+  long content_length_penalty_size; /* a connection with a
+                                       content-length bigger than
+                                       this is not considered
+                                       for pipelining */
+
+  long chunk_length_penalty_size; /* a connection with a chunk length
+                                     bigger than this is not
+                                     considered for pipelining */
+
+  struct curl_llist *pipelining_site_bl; /* List of sites that are blacklisted
+                                            from pipelining */
+
+  struct curl_llist *pipelining_server_bl; /* List of server types that are
+                                              blacklisted from pipelining */
+
   /* timer callback and user data pointer for the *socket() API */
   curl_multi_timer_callback timer_cb;
   void *timer_userp;