Problem: linger values other than -1 or 0 are unsafe

Solution: set defaults back to infinity, and add new context
option, ZMQ_BLOCKY that the user can set to false to get a
less surprising behavior on context termination. Eg.

    zmq_ctx_set (ctx, ZMQ_BLOCKY, false);

doc/zmq_ctx_get.txt

@@ -40,6 +40,12 @@ ZMQ_IPV6: Set IPv6 option
 ~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_IPV6' argument returns the IPv6 option for the context.
 
+ZMQ_BLOCKY: Get blocky setting
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The 'ZMQ_BLOCKY' argument returns 1 if the context will block on terminate,
+zero if the "block forever on context termination" gambit was disabled by
+setting ZMQ_BLOCKY to false on all new contexts.
+
 
 RETURN VALUE
 ------------
@@ -63,6 +69,10 @@ zmq_ctx_set (context, ZMQ_MAX_SOCKETS, 256);
 int max_sockets = zmq_ctx_get (context, ZMQ_MAX_SOCKETS);
 assert (max_sockets == 256);
 ----
+.Switching off the context deadlock gambit
+----
+zmq_ctx_set (ctx, ZMQ_BLOCKY, false);
+----
 
 
 SEE ALSO

doc/zmq_ctx_set.txt

@@ -21,6 +21,21 @@ The _zmq_ctx_set()_ function shall set the option specified by the
 The _zmq_ctx_set()_ function accepts the following options:
 
 
+ZMQ_BLOCKY: Fix blocky behavior
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+By default the context will block, forever, on a zmq_ctx_term call. The
+assumption behind this behavior is that abrupt termination will cause
+message loss. Most real applications use some form of handshaking to ensure
+applications receive termination messages, and then terminate the context
+with 'ZMQ_LINGER' set to zero on all sockets. This setting is an easier way
+to get the same result. When 'ZMQ_BLOCKY' is set to false, all new sockets
+are given a linger timeout of zero. You must still close all sockets before
+calling zmq_term.
+
+[horizontal]
+Default value:: false (old behavior)
+
+
 ZMQ_IO_THREADS: Set number of I/O threads
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 The 'ZMQ_IO_THREADS' argument specifies the size of the 0MQ thread pool to

include/zmq.h

@@ -304,6 +304,7 @@ ZMQ_EXPORT const char *zmq_msg_gets (zmq_msg_t *msg, const char *property);
 #define ZMQ_IDENTITY_FD 67
 #define ZMQ_SOCKS_PROXY 68
 #define ZMQ_XPUB_NODROP 69
+#define ZMQ_BLOCKY 70
 
 /*  Message options                                                           */
 #define ZMQ_MORE 1

src/ctx.cpp

@@ -65,6 +65,7 @@ zmq::ctx_t::ctx_t () :
     slots (NULL),
     max_sockets (clipped_maxsocket (ZMQ_MAX_SOCKETS_DFLT)),
     io_thread_count (ZMQ_IO_THREADS_DFLT),
+    blocky (true),
     ipv6 (false),
     thread_priority (ZMQ_THREAD_PRIORITY_DFLT),
     thread_sched_policy (ZMQ_THREAD_SCHED_POLICY_DFLT)
@@ -222,6 +223,12 @@ int zmq::ctx_t::set (int option_, int optval_)
         thread_sched_policy = optval_;
         opt_sync.unlock();
     }
+    else
+    if (option_ == ZMQ_BLOCKY && optval_ >= 0) {
+        opt_sync.lock ();
+        blocky = (optval_ != 0);
+        opt_sync.unlock ();
+    }
     else {
         errno = EINVAL;
         rc = -1;
@@ -243,6 +250,9 @@ int zmq::ctx_t::get (int option_)
     else
     if (option_ == ZMQ_IPV6)
         rc = ipv6;
+    else
+    if (option_ == ZMQ_BLOCKY)
+        rc = blocky;
     else {
         errno = EINVAL;
         rc = -1;

src/ctx.hpp

@@ -187,6 +187,9 @@ namespace zmq
         //  Number of I/O threads to launch.
         int io_thread_count;
 
+        //  Does context wait (possibly forever) on termination?
+        bool blocky;
+
         //  Is IPv6 enabled on this context?
         bool ipv6;
 

src/options.cpp

@@ -35,7 +35,7 @@ zmq::options_t::options_t () :
     rcvbuf (0),
     tos (0),
     type (-1),
-    linger (30000),
+    linger (-1),
     reconnect_ivl (100),
     reconnect_ivl_max (0),
     backlog (100),

src/socket_base.cpp

@@ -143,6 +143,7 @@ zmq::socket_base_t::socket_base_t (ctx_t *parent_, uint32_t tid_, int sid_) :
 {
     options.socket_id = sid_;
     options.ipv6 = (parent_->get (ZMQ_IPV6) != 0);
+    options.linger = parent_->get (ZMQ_BLOCKY)? -1: 0;
 }
 
 zmq::socket_base_t::~socket_base_t ()

tests/test_ctx_options.cpp

@@ -43,12 +43,23 @@ int main (void)
     assert (zmq_ctx_get (ctx, ZMQ_IPV6) == 1);
     
     void *router = zmq_socket (ctx, ZMQ_ROUTER);
-    int ipv6;
+    int value;
     size_t optsize = sizeof (int);
-    rc = zmq_getsockopt (router, ZMQ_IPV6, &ipv6, &optsize);
+    rc = zmq_getsockopt (router, ZMQ_IPV6, &value, &optsize);
+    assert (rc == 0);
+    assert (value == 1);
+    rc = zmq_getsockopt (router, ZMQ_LINGER, &value, &optsize);
+    assert (rc == 0);
+    assert (value == -1);
+    rc = zmq_close (router);
     assert (rc == 0);
-    assert (ipv6);
     
+    rc = zmq_ctx_set (ctx, ZMQ_BLOCKY, false);
+    assert (zmq_ctx_get (ctx, ZMQ_BLOCKY) == 0);
+    router = zmq_socket (ctx, ZMQ_ROUTER);
+    rc = zmq_getsockopt (router, ZMQ_LINGER, &value, &optsize);
+    assert (rc == 0);
+    assert (value == 0);
     rc = zmq_close (router);
     assert (rc == 0);