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authorgdamore <gdamore@users.noreply.github.com>2025-01-02 03:46:39 +0000
committergdamore <gdamore@users.noreply.github.com>2025-01-02 03:46:39 +0000
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+
+</style>
+<h1 id="contexts"><a class="header" href="#contexts">Contexts</a></h1>
+<p>Contexts <a name="a001"></a> in Scalability Protocols provide for isolation of protocol-specific
+state machines and associated data, allowing multiple <a name="a002"></a>concurrent <a name="a003"></a>state machines (or transactions)
+to coexist on a single <a href="/TODO.html">socket</a>.</p>
+<p>For example, a <a href="/proto/rep.html">REP</a> server may wish to allow many requests to be serviced concurrently,
+even though some jobs may take significant time to process. Contexts provide for this ability.</p>
+<p>Not all protocols have contexts, because many protocols simply have no state to manage.
+The following protocols support contexts:</p>
+<ul>
+<li><a href="/proto/rep.html">REP</a></li>
+<li><a href="/proto/req.html">REQ</a></li>
+<li><a href="/proto/respondent.html">RESPONDENT</a></li>
+<li><a href="/proto/surveyor.html">SURVEYOR</a></li>
+<li><a href="/proto/sub.html">SUB</a></li>
+</ul>
+<p>For these protocols, the socket will also have a single, default, context that is used when
+performing send or receive operations on the socket directly.</p>
+<p>Other protocols are stateless, at least with respect to message processing, and have no use for
+contexts. For the same reason, <a href="/api/sock.html#raw-mode-sockets">raw</a> mode sockets do not support contexts.</p>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>Developers with experience with [libnanomsg] may be used to using <a href="/api/sock.html#raw-mode-sockets">raw</a> sockets for concurrency.
+Contexts provide a superior solution, as they are much easier to use, less error prone, and allow
+for easy control of the amount of concurrency used on any given socket.</p>
+</div>
+<p>One drawback of contexts is that they cannot be used with file descriptor polling using
+<a href="/api/sock.html#polling-socket-events"><code>nng_socket_get_recv_poll_fd</code></a> or <a href="/api/sock.html#polling-socket-events"><code>nng_socket_get_send_poll_fd</code></a>.</p>
+<h2 id="context-structure"><a class="header" href="#context-structure">Context Structure</a></h2>
+<pre><code class="language-c">#define NNG_CTX_INITIALIZER // opaque value
+
+typedef struct nng_ctx_s nng_ctx;
+</code></pre>
+<p>The <a name="a004"></a><code>nng_ctx</code> structure represents context. This is a handle, and
+the members of it are opaque. However, unlike a pointer, it is passed by value.</p>
+<p>A context may be initialized statically with the <a name="a005"></a><code>NNG_CTX_INITIALIZER</code> macro,
+to ensure that it cannot be confused with a valid open context.</p>
+<h2 id="creating-a-context"><a class="header" href="#creating-a-context">Creating a Context</a></h2>
+<pre><code class="language-c">int nng_ctx_open(nng_ctx *ctxp, nng_socket s);
+</code></pre>
+<p>The <a name="a006"></a><code>nng_ctx_open</code> function creates a separate context to be used with the <a href="/TODO.html">socket</a> <em>s</em>,
+and returns it at the location pointed by <em>ctxp</em>.</p>
+<h2 id="context-identity"><a class="header" href="#context-identity">Context Identity</a></h2>
+<pre><code class="language-c">int nng_ctx_id(nng_ctx c);
+</code></pre>
+<p>The <a name="a007"></a><code>nng_ctx_id</code> function returns a positive identifier for the context <em>c</em> if it is valid.
+Otherwise it returns <code>-1</code>.</p>
+<p>A context is considered valid if it was ever opened with <a href="/api/ctx.html#creating-a-context"><code>nng_ctx_open</code></a> function.
+Contexts that are allocated on the stack or statically should be initialized with the macro <a href="/api/ctx.html#context-structure"><code>NNG_CTX_INITIALIZER</code></a>
+to ensure that they cannot be confused with a valid context before they are opened.</p>
+<h2 id="closing-a-context"><a class="header" href="#closing-a-context">Closing a Context</a></h2>
+<pre><code class="language-c">int nng_ctx_close(nng_ctx ctx);
+</code></pre>
+<p>The <a name="a008"></a><code>nng_ctx_close</code> function closes the context <em>ctx</em>.
+Messages that have been submitted for sending may be flushed or delivered,
+depending upon the transport.</p>
+<p>Further attempts to use the context after this call returns will result in <code>NNG_ECLOSED</code>.
+Threads waiting for operations on the context when this
+call is executed may also return with an <code>NNG_ECLOSED</code> result.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>Closing the socket associated with <em>ctx</em> using <code>nng_socket_close</code>] also closes this context.</p>
+</div>
+<h2 id="sending-messages"><a class="header" href="#sending-messages">Sending Messages</a></h2>
+<pre><code class="language-c">int nng_ctx_sendmsg(nng_ctx ctx, nng_msg *msg, int flags);
+void nng_ctx_send(nng_ctx ctx, nng_aio *aio);
+</code></pre>
+<p>These functions (<a name="a009"></a><code>nng_ctx_sendmsg</code> and <a name="a010"></a><code>nng_ctx_send</code>) send
+messages over the socket <em>s</em>. The differences in their behaviors are as follows.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>The semantics of what sending a message means varies from protocol to
+protocol, so examination of the protocol documentation is encouraged.
+Additionally, some protocols may not support sending at all or may require other pre-conditions first.
+(For example, <a href="/proto/rep.html">REP</a> sockets cannot normally send data until they have first received a request,
+while <a href="/proto/sub.html">SUB</a> sockets can only receive data and never send it.)</p>
+</div>
+<h3 id="nng_ctx_sendmsg"><a class="header" href="#nng_ctx_sendmsg">nng_ctx_sendmsg</a></h3>
+<p>The <code>nng_ctx_sendmsg</code> function sends the <em>msg</em> over the context <em>ctx</em>.</p>
+<p>If this function returns zero, then the socket will dispose of <em>msg</em> when the transmission is complete.
+If the function returns a non-zero status, then the call retains the responsibility for disposing of <em>msg</em>.</p>
+<p>The <em>flags</em> can contain the value <a href="/TODO.html"><code>NNG_FLAG_NONBLOCK</code></a>, indicating that the function should not wait if the socket
+cannot accept more data for sending. In such a case, it will return <a href="/api/errors.html#NNG_EAGAIN"><code>NNG_EAGAIN</code></a>.</p>
+<h3 id="nng_ctx_send"><a class="header" href="#nng_ctx_send">nng_ctx_send</a></h3>
+<p>The <code>nng_ctx_send</code> function sends a message asynchronously, using the <a href="/api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a> <em>aio</em>, over the context <em>ctx</em>.
+The message to send must have been set on <em>aio</em> using the <a href="/api/aio.html#messages"><code>nng_aio_set_msg</code></a> function.</p>
+<p>If the operation completes successfully, then the context will have disposed of the message.
+However, if it fails, then callback of <em>aio</em> should arrange for a final disposition of the message.
+(The message can be retrieved from <em>aio</em> with <a href="/api/aio.html#messages"><code>nng_aio_get_msg</code></a>.)</p>
+<p>Note that callback associated with <em>aio</em> may be called <em>before</em> the message is finally delivered to the recipient.
+For example, the message may be sitting in queue, or located in TCP buffers, or even in flight.</p>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>This is the preferred function to use for sending data on a context. While it does require a few extra
+steps on the part of the application, the lowest latencies and highest performance will be achieved by using
+this function instead of <a href="/api/ctx.html#nng_ctx_sendmsg"><code>nng_ctx_sendmsg</code></a>.</p>
+</div>
+<h2 id="receiving-messages"><a class="header" href="#receiving-messages">Receiving Messages</a></h2>
+<pre><code class="language-c">int nng_ctx_recvmsg(nng_ctx ctx, nng_msg **msgp, int flags);
+void nng_ctx_recv(nng_ctx ctx, nng_aio *aio);
+</code></pre>
+<p>These functions (, <a name="a011"></a><code>nng_ctx_recvmsg</code> and <a name="a012"></a><code>nng_ctx_recv</code>) receive
+messages over the context <em>ctx</em>. The differences in their behaviors are as follows.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>The semantics of what receving a message means varies from protocol to
+protocol, so examination of the protocol documentation is encouraged.
+Additionally, some protocols may not support receiving at all or may require other pre-conditions first.
+(For example, <a href="/proto/req.html">REQ</a> sockets cannot normally receive data until they have first sent a request.)</p>
+</div>
+<h3 id="nng_recvmsg"><a class="header" href="#nng_recvmsg">nng_recvmsg</a></h3>
+<p>The <code>nng_ctx_recvmsg</code> function receives a message and stores a pointer to the <a href="/api/msg.html#message-structure"><code>nng_msg</code></a> for that message in <em>msgp</em>.</p>
+<p>The <em>flags</em> can contain the value <a href="/TODO.html"><code>NNG_FLAG_NONBLOCK</code></a>, indicating that the function should not wait if the socket
+has no messages available to receive. In such a case, it will return <a href="/api/errors.html#NNG_EAGAIN"><code>NNG_EAGAIN</code></a>.</p>
+<h3 id="nng_recv_aio"><a class="header" href="#nng_recv_aio">nng_recv_aio</a></h3>
+<p>The <code>nng_ctx_send</code> function receives a message asynchronously, using the <a href="/api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a> <em>aio</em>, over the context <em>ctx</em>.
+On success, the received message can be retrieved from the <em>aio</em> using the <a href="/api/aio.html#messages"><code>nng_aio_get_msg</code></a> function.</p>
+<div class="mdbook-alerts mdbook-alerts-note">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ note
+</p>
+<p>It is important that the application retrieves the message, and disposes of it accordingly.
+Failure to do so will leak the memory.</p>
+</div>
+<div class="mdbook-alerts mdbook-alerts-tip">
+<p class="mdbook-alerts-title">
+ <span class="mdbook-alerts-icon"></span>
+ tip
+</p>
+<p>This is the preferred function to use for receiving data on a context. While it does require a few extra
+steps on the part of the application, the lowest latencies and highest performance will be achieved by using
+this function instead of <a href="/api/ctx.html#nng_ctx_recvmsg"><code>nng_ctx_recvmsg</code></a>.</p>
+</div>
+<h2 id="context-options"><a class="header" href="#context-options">Context Options</a></h2>
+<pre><code class="language-c">int nng_ctx_get_bool(nng_ctx ctx, const char *opt, bool *valp);
+int nng_ctx_get_int(nng_ctx ctx, const char *opt, int *valp);
+int nng_ctx_get_ms(nng_ctx ctx, const char *opt, nng_duration *valp);
+int nng_ctx_get_size(nng_ctx ctx, const char *opt, size_t *valp);
+int nng_ctx_get_uint64(nng_ctx ctx, const char *opt, uint64_t *valp);
+
+int nng_ctx_set_bool(nng_ctx ctx, const char *opt, int val);
+int nng_ctx_set_int(nng_ctx ctx, const char *opt, int val);
+int nng_ctx_set_ms(nng_ctx ctx, const char *opt, nng_duration val);
+int nng_ctx_set_size(nng_ctx ctx, const char *opt, size_t val);
+int nng_ctx_set_uint64(nng_ctx ctx, const char *opt, uint64_t val);
+</code></pre>
+<p>These functions are used to retrieve or change the value of an option named <em>opt</em> from the context <em>ctx</em>.
+The <code>nng_ctx_get_</code> functions retrieve the value, and store it in the location <em>valp</em> references.
+The <code>nng_ctx_set_</code> functions change the value for the <em>ctx</em>, taking it from <em>val</em>.</p>
+<p>These functions access an option as a specific type. The protocol will have details about which options
+are available for contexts, and which type they may be accessed using.</p>
+<h2 id="examples"><a class="header" href="#examples">Examples</a></h2>
+<p>These examples show building blocks for a concurrent service based on contexts.</p>
+<h3 id="example-1-context-echo-server"><a class="header" href="#example-1-context-echo-server">Example 1: Context Echo Server</a></h3>
+<p>The following program fragment demonstrates the use of contexts to implement
+a concurrent <a href="/proto/rep.html">REP</a> service that simply echos messages back
+to the sender.</p>
+<pre><code class="language-c">struct echo_context {
+ nng_ctx ctx;
+ nng_aio *aio;
+ enum { INIT, RECV, SEND } state;
+};
+
+void
+echo(void *arg)
+{
+ struct echo_context *ec = arg;
+
+ switch (ec-&gt;state) {
+ case INIT:
+ ec-&gt;state = RECV;
+ nng_ctx_recv(ec-&gt;ctx, ec-&gt;aio);
+ return;
+ case RECV:
+ if (nng_aio_result(ec-&gt;aio) != 0) {
+ // ... handle error
+ }
+ // We reuse the message on the ec-&gt;aio
+ ec-&gt;state = SEND;
+ nng_ctx_send(ec-&gt;ctx, ec-&gt;aio);
+ return;
+ case SEND:
+ if (nng_aio_result(ec-&gt;aio) != 0) {
+ // ... handle error
+ }
+ ec-&gt;state = RECV;
+ nng_ctx_recv(ec-&gt;ctx, ec-&gt;aio);
+ return;
+ }
+}
+</code></pre>
+<h3 id="example-2-starting-the-echo-service"><a class="header" href="#example-2-starting-the-echo-service">Example 2: Starting the Echo Service</a></h3>
+<p>Given the above fragment, the following example shows setting up the service.
+It assumes that the <a href="/TODO.html">socket</a> has already been
+created and any transports set up as well with functions such as <a href="/TODO.html"><code>nng_dial</code></a> or <a href="/TODO.html"><code>nng_listen</code></a>.</p>
+<pre><code class="language-c">
+#define CONCURRENCY 1024
+
+static struct echo_context ecs[CONCURRENCY];
+
+void
+start_echo_service(nng_socket rep_socket)
+{
+ for (int i = 0; i &lt; CONCURRENCY; i++) {
+ // error checks elided for clarity
+ nng_ctx_open(&amp;ecs[i].ctx, rep_socket);
+ nng_aio_alloc(&amp;ecs[i].aio, echo, ecs+i);
+ ecs[i].state = INIT;
+ echo(ecs+i); // start it running
+ }
+}
+</code></pre>
+<!-- Symbol cross reference -->
+<!-- Macros -->
+<!-- Protocols -->
+<!-- Transports -->
+<!-- Concept index -->
+
+ </main>
+
+ <nav class="nav-wrapper" aria-label="Page navigation">
+ <!-- Mobile navigation buttons -->
+ <a rel="prev" href="../api/sock.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
+ <i class="fa fa-angle-left"></i>
+ </a>
+
+ <a rel="next prefetch" href="../api/memory.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
+ <i class="fa fa-angle-right"></i>
+ </a>
+
+ <div style="clear: both"></div>
+ </nav>
+ </div>
+ </div>
+
+ <nav class="nav-wide-wrapper" aria-label="Page navigation">
+ <a rel="prev" href="../api/sock.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
+ <i class="fa fa-angle-left"></i>
+ </a>
+
+ <a rel="next prefetch" href="../api/memory.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
+ <i class="fa fa-angle-right"></i>
+ </a>
+ </nav>
+
+ </div>
+
+
+
+
+ <script>
+ window.playground_copyable = true;
+ </script>
+
+
+ <script src="../elasticlunr.min.js"></script>
+ <script src="../mark.min.js"></script>
+ <script src="../searcher.js"></script>
+
+ <script src="../clipboard.min.js"></script>
+ <script src="../highlight.js"></script>
+ <script src="../book.js"></script>
+
+ <!-- Custom JS scripts -->
+ <script src="../theme/pagetoc.js"></script>
+
+
+ </div>
+ </body>
+</html>
diff --git a/ref/api/index.html b/ref/api/index.html
index db3f30c3..5372ced4 100644
--- a/ref/api/index.html
+++ b/ref/api/index.html
@@ -233,6 +233,7 @@ include the <code>nng/nng.h</code> header file like so:</p>
<li><a href="init.html">Initialization</a></li>
<li><a href="msg.html">Messages</a></li>
<li><a href="sock.html">Sockets</a></li>
+<li><a href="ctx.html">Contexts</a></li>
<li><a href="memory.html">Memory</a></li>
<li><a href="time.html">Time</a></li>
<li><a href="url.html">URLs</a></li>
diff --git a/ref/api/memory.html b/ref/api/memory.html
index 32319564..ddacea19 100644
--- a/ref/api/memory.html
+++ b/ref/api/memory.html
@@ -278,7 +278,7 @@ can be used to deallocate strings allocated with <a href="/api/memory.html#dupli
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
- <a rel="prev" href="../api/sock.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
+ <a rel="prev" href="../api/ctx.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
@@ -292,7 +292,7 @@ can be used to deallocate strings allocated with <a href="/api/memory.html#dupli
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
- <a rel="prev" href="../api/sock.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
+ <a rel="prev" href="../api/ctx.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
diff --git a/ref/api/sock.html b/ref/api/sock.html
index 215726e0..cdb4b824 100644
--- a/ref/api/sock.html
+++ b/ref/api/sock.html
@@ -485,7 +485,7 @@ Failure to do so will leak the memory.</p>
</p>
<p>This is the preferred function to use for receiving data on a socket. While it does require a few extra
steps on the part of the application, the lowest latencies and highest performance will be achieved by using
-this function instead of <a href="/TODO.html"><code>nng_recv</code></a> or <a href="/TODO.html"><code>nng_recvmsg</code></a>.</p>
+this function instead of <a href="/TODO.html"><code>nng_recv</code></a> or <a href="/api/sock.html#nng_recvmsg"><code>nng_recvmsg</code></a>.</p>
</div>
<h2 id="polling-socket-events"><a class="header" href="#polling-socket-events">Polling Socket Events</a></h2>
<pre><code class="language-c">int nng_socket_get_recv_poll_fd(nng_socket s, int *fdp);
@@ -586,7 +586,7 @@ int main(int argc, char **argv) {
}
</code></pre>
<h3 id="example-3-watching-a-periodic-timestamp"><a class="header" href="#example-3-watching-a-periodic-timestamp">Example 3: Watching a Periodic Timestamp</a></h3>
-<p>This example demonstrates the use of <a href="/api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a>, [<code>nng_recv_aio</code>], to build a client to
+<p>This example demonstrates the use of <a href="/api/aio.html#asynchronous-io-handle"><code>nng_aio</code></a>, <a href="/api/sock.html#nng_recv_aio"><code>nng_recv_aio</code></a>, to build a client to
watch for messages received from the service created in Example 2.
Error handling is elided for the sake of clarity.</p>
<pre><code class="language-c">#include &lt;stdlib.h&gt;
@@ -645,7 +645,7 @@ int main(int argc, char **argv) {
<i class="fa fa-angle-left"></i>
</a>
- <a rel="next prefetch" href="../api/memory.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
+ <a rel="next prefetch" href="../api/ctx.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
@@ -659,7 +659,7 @@ int main(int argc, char **argv) {
<i class="fa fa-angle-left"></i>
</a>
- <a rel="next prefetch" href="../api/memory.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
+ <a rel="next prefetch" href="../api/ctx.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2026-01-18 10:23:20 +0000