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Agent.html
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Agent.html
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<!DOCTYPE html>
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Class: Concurrent::Agent
— Concurrent Ruby
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<div id="content"><h1>Class: Concurrent::Agent
</h1>
<div class="box_info">
<dl>
<dt>Inherits:</dt>
<dd>
<span class="inheritName"><span class='object_link'>Synchronization::LockableObject</span></span>
<ul class="fullTree">
<li>Object</li>
<li class="next"><span class='object_link'>Synchronization::LockableObject</span></li>
<li class="next">Concurrent::Agent</li>
</ul>
<a href="#" class="inheritanceTree">show all</a>
</dd>
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<dl>
<dt>Includes:</dt>
<dd><span class='object_link'><a href="Concern/Observable.html" title="Concurrent::Concern::Observable (module)">Concern::Observable</a></span></dd>
</dl>
<dl>
<dt>Defined in:</dt>
<dd>lib/concurrent/agent.rb</dd>
</dl>
</div>
<h2>Overview</h2><div class="docstring">
<div class="discussion">
<p><code>Agent</code> is inspired by Clojure's <a href="http://clojure.org/agents">agent</a>
function. An agent is a shared, mutable variable providing independent,
uncoordinated, <em>asynchronous</em> change of individual values. Best used when
the value will undergo frequent, complex updates. Suitable when the result
of an update does not need to be known immediately. <code>Agent</code> is (mostly)
functionally equivalent to Clojure's agent, except where the runtime
prevents parity.</p>
<p>Agents are reactive, not autonomous - there is no imperative message loop
and no blocking receive. The state of an Agent should be itself immutable
and the <code>#value</code> of an Agent is always immediately available for reading by
any thread without any messages, i.e. observation does not require
cooperation or coordination.</p>
<p>Agent action dispatches are made using the various <code>#send</code> methods. These
methods always return immediately. At some point later, in another thread,
the following will happen:</p>
<ol>
<li>The given <code>action</code> will be applied to the state of the Agent and the
<code>args</code>, if any were supplied.</li>
<li>The return value of <code>action</code> will be passed to the validator lambda,
if one has been set on the Agent.</li>
<li>If the validator succeeds or if no validator was given, the return value
of the given <code>action</code> will become the new <code>#value</code> of the Agent. See
<code>#initialize</code> for details.</li>
<li>If any observers were added to the Agent, they will be notified. See
<code>#add_observer</code> for details.</li>
<li>If during the <code>action</code> execution any other dispatches are made (directly
or indirectly), they will be held until after the <code>#value</code> of the Agent
has been changed.</li>
</ol>
<p>If any exceptions are thrown by an action function, no nested dispatches
will occur, and the exception will be cached in the Agent itself. When an
Agent has errors cached, any subsequent interactions will immediately throw
an exception, until the agent's errors are cleared. Agent errors can be
examined with <code>#error</code> and the agent restarted with <code>#restart</code>.</p>
<p>The actions of all Agents get interleaved amongst threads in a thread pool.
At any point in time, at most one action for each Agent is being executed.
Actions dispatched to an agent from another single agent or thread will
occur in the order they were sent, potentially interleaved with actions
dispatched to the same agent from other sources. The <code>#send</code> method should
be used for actions that are CPU limited, while the <code>#send_off</code> method is
appropriate for actions that may block on IO.</p>
<p>Unlike in Clojure, <code>Agent</code> cannot participate in <code>Concurrent::TVar</code> transactions.</p>
<h2>Example</h2>
<pre class="code ruby"><code class="ruby"><span class='kw'>def</span> <span class='id identifier rubyid_next_fibonacci'>next_fibonacci</span><span class='lparen'>(</span><span class='id identifier rubyid_set'>set</span> <span class='op'>=</span> <span class='kw'>nil</span><span class='rparen'>)</span>
<span class='kw'>return</span> <span class='lbracket'>[</span><span class='int'>0</span><span class='comma'>,</span> <span class='int'>1</span><span class='rbracket'>]</span> <span class='kw'>if</span> <span class='id identifier rubyid_set'>set</span><span class='period'>.</span><span class='id identifier rubyid_nil?'>nil?</span>
<span class='id identifier rubyid_set'>set</span> <span class='op'>+</span> <span class='lbracket'>[</span><span class='id identifier rubyid_set'>set</span><span class='lbracket'>[</span><span class='op'>-</span><span class='int'>2</span><span class='op'>..</span><span class='op'>-</span><span class='int'>1</span><span class='rbracket'>]</span><span class='period'>.</span><span class='id identifier rubyid_reduce'>reduce</span><span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_sum'>sum</span><span class='comma'>,</span><span class='id identifier rubyid_x'>x</span><span class='op'>|</span> <span class='id identifier rubyid_sum'>sum</span> <span class='op'>+</span> <span class='id identifier rubyid_x'>x</span> <span class='rbrace'>}</span><span class='rbracket'>]</span>
<span class='kw'>end</span>
<span class='comment'># create an agent with an initial value
</span><span class='id identifier rubyid_agent'>agent</span> <span class='op'>=</span> <span class='const'><span class='object_link'><a href="../Concurrent.html" title="Concurrent (module)">Concurrent</a></span></span><span class='op'>::</span><span class='const'>Agent</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Agent#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='id identifier rubyid_next_fibonacci'>next_fibonacci</span><span class='rparen'>)</span>
<span class='comment'># send a few update requests
</span><span class='int'>5</span><span class='period'>.</span><span class='id identifier rubyid_times'>times</span> <span class='kw'>do</span>
<span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_send'>send</span><span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_set'>set</span><span class='op'>|</span> <span class='id identifier rubyid_next_fibonacci'>next_fibonacci</span><span class='lparen'>(</span><span class='id identifier rubyid_set'>set</span><span class='rparen'>)</span> <span class='rbrace'>}</span>
<span class='kw'>end</span>
<span class='comment'># wait for them to complete
</span><span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_await'>await</span>
<span class='comment'># get the current value
</span><span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span> <span class='comment'>#=> [0, 1, 1, 2, 3, 5, 8]
</span></code></pre>
<h2>Observation</h2>
<p>Agents support observers through the Observable mixin module.
Notification of observers occurs every time an action dispatch returns and
the new value is successfully validated. Observation will <em>not</em> occur if the
action raises an exception, if validation fails, or when a <span class='object_link'><a href="#restart-instance_method" title="Concurrent::Agent#restart (method)">#restart</a></span> occurs.</p>
<p>When notified the observer will receive three arguments: <code>time</code>, <code>old_value</code>,
and <code>new_value</code>. The <code>time</code> argument is the time at which the value change
occurred. The <code>old_value</code> is the value of the Agent when the action began
processing. The <code>new_value</code> is the value to which the Agent was set when the
action completed. Note that <code>old_value</code> and <code>new_value</code> may be the same.
This is not an error. It simply means that the action returned the same
value.</p>
<h2>Nested Actions</h2>
<p>It is possible for an Agent action to post further actions back to itself.
The nested actions will be enqueued normally then processed <em>after</em> the
outer action completes, in the order they were sent, possibly interleaved
with action dispatches from other threads. Nested actions never deadlock
with one another and a failure in a nested action will never affect the
outer action.</p>
<p>Nested actions can be called using the Agent reference from the enclosing
scope or by passing the reference in as a "send" argument. Nested actions
cannot be post using <code>self</code> from within the action block/proc/lambda; <code>self</code>
in this context will not reference the Agent. The preferred method for
dispatching nested actions is to pass the Agent as an argument. This allows
Ruby to more effectively manage the closing scope.</p>
<p>Prefer this:</p>
<pre class="code ruby"><code class="ruby"><span class='id identifier rubyid_agent'>agent</span> <span class='op'>=</span> <span class='const'><span class='object_link'><a href="../Concurrent.html" title="Concurrent (module)">Concurrent</a></span></span><span class='op'>::</span><span class='const'>Agent</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Agent#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='int'>0</span><span class='rparen'>)</span>
<span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_send'>send</span><span class='lparen'>(</span><span class='id identifier rubyid_agent'>agent</span><span class='rparen'>)</span> <span class='kw'>do</span> <span class='op'>|</span><span class='id identifier rubyid_value'>value</span><span class='comma'>,</span> <span class='id identifier rubyid_this'>this</span><span class='op'>|</span>
<span class='id identifier rubyid_this'>this</span><span class='period'>.</span><span class='id identifier rubyid_send'>send</span> <span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_v'>v</span><span class='op'>|</span> <span class='id identifier rubyid_v'>v</span> <span class='op'>+</span> <span class='int'>42</span> <span class='rbrace'>}</span>
<span class='float'>3.14</span>
<span class='kw'>end</span>
<span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_value'>value</span> <span class='comment'>#=> 45.14
</span></code></pre>
<p>Over this:</p>
<pre class="code ruby"><code class="ruby"><span class='id identifier rubyid_agent'>agent</span> <span class='op'>=</span> <span class='const'><span class='object_link'><a href="../Concurrent.html" title="Concurrent (module)">Concurrent</a></span></span><span class='op'>::</span><span class='const'>Agent</span><span class='period'>.</span><span class='id identifier rubyid_new'><span class='object_link'><a href="#initialize-instance_method" title="Concurrent::Agent#initialize (method)">new</a></span></span><span class='lparen'>(</span><span class='int'>0</span><span class='rparen'>)</span>
<span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_send'>send</span> <span class='kw'>do</span> <span class='op'>|</span><span class='id identifier rubyid_value'>value</span><span class='op'>|</span>
<span class='id identifier rubyid_agent'>agent</span><span class='period'>.</span><span class='id identifier rubyid_send'>send</span> <span class='lbrace'>{</span><span class='op'>|</span><span class='id identifier rubyid_v'>v</span><span class='op'>|</span> <span class='id identifier rubyid_v'>v</span> <span class='op'>+</span> <span class='int'>42</span> <span class='rbrace'>}</span>
<span class='float'>3.14</span>
<span class='kw'>end</span>
</code></pre>
<p><strong>NOTE</strong> Never, <em>under any circumstances</em>, call any of the "await" methods
(<span class='object_link'><a href="#await-instance_method" title="Concurrent::Agent#await (method)">#await</a></span>, <span class='object_link'><a href="#await_for-instance_method" title="Concurrent::Agent#await_for (method)">#await_for</a></span>, <span class='object_link'><a href="#await_for!-instance_method" title="Concurrent::Agent#await_for! (method)">#await_for!</a></span>, and <span class='object_link'><a href="#wait-instance_method" title="Concurrent::Agent#wait (method)">#wait</a></span>) from within an action
block/proc/lambda. The call will block the Agent and will always fail.
Calling either <span class='object_link'><a href="#await-instance_method" title="Concurrent::Agent#await (method)">#await</a></span> or <span class='object_link'><a href="#wait-instance_method" title="Concurrent::Agent#wait (method)">#wait</a></span> (with a timeout of <code>nil</code>) will
hopelessly deadlock the Agent with no possibility of recovery.</p>
<h2>Thread-safe Variable Classes</h2>
<p>Each of the thread-safe variable classes is designed to solve a different
problem. In general:</p>
<ul>
<li><em><span class='object_link'><a href="" title="Concurrent::Agent (class)">Agent</a></span>:</em> Shared, mutable variable providing independent,
uncoordinated, <em>asynchronous</em> change of individual values. Best used when
the value will undergo frequent, complex updates. Suitable when the result
of an update does not need to be known immediately.</li>
<li><em><span class='object_link'><a href="Atom.html" title="Concurrent::Atom (class)">Atom</a></span>:</em> Shared, mutable variable providing independent,
uncoordinated, <em>synchronous</em> change of individual values. Best used when
the value will undergo frequent reads but only occasional, though complex,
updates. Suitable when the result of an update must be known immediately.</li>
<li><em><span class='object_link'><a href="AtomicReference.html" title="Concurrent::AtomicReference (class)">AtomicReference</a></span>:</em> A simple object reference that can be
atomically. Updates are synchronous but fast. Best used when updates a
simple set operations. Not suitable when updates are complex.
<span class='object_link'><a href="AtomicBoolean.html" title="Concurrent::AtomicBoolean (class)">AtomicBoolean</a></span> and <span class='object_link'><a href="AtomicFixnum.html" title="Concurrent::AtomicFixnum (class)">AtomicFixnum</a></span> are similar
but optimized for the given data type.</li>
<li><em><span class='object_link'><a href="Exchanger.html" title="Concurrent::Exchanger (class)">Exchanger</a></span>:</em> Shared, stateless synchronization point. Used
when two or more threads need to exchange data. The threads will pair then
block on each other until the exchange is complete.</li>
<li><em><span class='object_link'><a href="MVar.html" title="Concurrent::MVar (class)">MVar</a></span>:</em> Shared synchronization point. Used when one thread
must give a value to another, which must take the value. The threads will
block on each other until the exchange is complete.</li>
<li><em><span class='object_link'><a href="ThreadLocalVar.html" title="Concurrent::ThreadLocalVar (class)">ThreadLocalVar</a></span>:</em> Shared, mutable, isolated variable which
holds a different value for each thread which has access. Often used as
an instance variable in objects which must maintain different state
for different threads.</li>
<li><em><span class='object_link'><a href="TVar.html" title="Concurrent::TVar (class)">TVar</a></span>:</em> Shared, mutable variables which provide
<em>coordinated</em>, <em>synchronous</em>, change of <em>many</em> stated. Used when multiple
value must change together, in an all-or-nothing transaction.</li>
</ul>
</div>
</div>
<div class="tags">
<p class="tag_title">See Also:</p>
<ul class="see">
<li><a href="http://clojure.org/Agents" target="_parent" title="Clojure Agents">Clojure Agents</a></li>
<li><a href="http://clojure.org/state" target="_parent" title="Values and Change - Clojure's approach to Identity and State">Values and Change - Clojure's approach to Identity and State</a></li>
</ul>
</div><h2>Defined Under Namespace</h2>
<p class="children">
<strong class="classes">Classes:</strong> <span class='object_link'><a href="Agent/Error.html" title="Concurrent::Agent::Error (class)">Error</a></span>, <span class='object_link'><a href="Agent/ValidationError.html" title="Concurrent::Agent::ValidationError (class)">ValidationError</a></span>
</p>
<h2>Instance Attribute Summary <small><a href="#" class="summary_toggle">collapse</a></small></h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#error_mode-instance_method" title="#error_mode (instance method)">#<strong>error_mode</strong> ⇒ undocumented </a>
</span>
<span class="note title readonly">readonly</span>
<span class="summary_desc"><div class='inline'><p>The error mode this Agent is operating in.</p>
</div></span>
</li>
</ul>
<h2>
Class Method Summary
<small><a href="#" class="summary_toggle">collapse</a></small>
</h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#await-class_method" title="await (class method)">.<strong>await</strong>(*agents) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread (indefinitely!) until all actions dispatched thus far to all the given Agents, from this thread or nested by the given Agents, have occurred.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#await_for-class_method" title="await_for (class method)">.<strong>await_for</strong>(timeout, *agents) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread until all actions dispatched thus far to all the given Agents, from this thread or nested by the given Agents, have occurred, or the timeout (in seconds) has elapsed.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#await_for!-class_method" title="await_for! (class method)">.<strong>await_for!</strong>(timeout, *agents) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread until all actions dispatched thus far to all the given Agents, from this thread or nested by the given Agents, have occurred, or the timeout (in seconds) has elapsed.</p>
</div></span>
</li>
</ul>
<h2>
Instance Method Summary
<small><a href="#" class="summary_toggle">collapse</a></small>
</h2>
<ul class="summary">
<li class="public ">
<span class="summary_signature">
<a href="#<<-instance_method" title="#<< (instance method)">#<strong><<</strong>(action) ⇒ Concurrent::Agent </a>
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#add_observer-instance_method" title="#add_observer (instance method)">#<strong>add_observer</strong>(observer = nil, func = :update, &block) ⇒ Object </a>
</span>
<span class="note title not_defined_here">
included
from <span class='object_link'><a href="Concern/Observable.html#add_observer-instance_method" title="Concurrent::Concern::Observable#add_observer (method)">Concern::Observable</a></span>
</span>
<span class="summary_desc"><div class='inline'><p>Adds an observer to this set.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#await-instance_method" title="#await (instance method)">#<strong>await</strong> ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread (indefinitely!) until all actions dispatched thus far, from this thread or nested by the Agent, have occurred.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#await_for-instance_method" title="#await_for (instance method)">#<strong>await_for</strong>(timeout) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread until all actions dispatched thus far, from this thread or nested by the Agent, have occurred, or the timeout (in seconds) has elapsed.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#await_for!-instance_method" title="#await_for! (instance method)">#<strong>await_for!</strong>(timeout) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread until all actions dispatched thus far, from this thread or nested by the Agent, have occurred, or the timeout (in seconds) has elapsed.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#count_observers-instance_method" title="#count_observers (instance method)">#<strong>count_observers</strong> ⇒ Integer </a>
</span>
<span class="note title not_defined_here">
included
from <span class='object_link'><a href="Concern/Observable.html#count_observers-instance_method" title="Concurrent::Concern::Observable#count_observers (method)">Concern::Observable</a></span>
</span>
<span class="summary_desc"><div class='inline'><p>Return the number of observers associated with this object.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#delete_observer-instance_method" title="#delete_observer (instance method)">#<strong>delete_observer</strong>(observer) ⇒ Object </a>
</span>
<span class="note title not_defined_here">
included
from <span class='object_link'><a href="Concern/Observable.html#delete_observer-instance_method" title="Concurrent::Concern::Observable#delete_observer (method)">Concern::Observable</a></span>
</span>
<span class="summary_desc"><div class='inline'><p>Remove <code>observer</code> as an observer on this object so that it will no longer receive notifications.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#delete_observers-instance_method" title="#delete_observers (instance method)">#<strong>delete_observers</strong> ⇒ Observable </a>
</span>
<span class="note title not_defined_here">
included
from <span class='object_link'><a href="Concern/Observable.html#delete_observers-instance_method" title="Concurrent::Concern::Observable#delete_observers (method)">Concern::Observable</a></span>
</span>
<span class="summary_desc"><div class='inline'><p>Remove all observers associated with this object.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#error-instance_method" title="#error (instance method)">#<strong>error</strong> ⇒ nil, Error </a>
(also: #reason)
</span>
<span class="summary_desc"><div class='inline'><p>When <span class='object_link'><a href="#failed%3F-instance_method" title="Concurrent::Agent#failed? (method)">#failed?</a></span> and <span class='object_link'><a href="#error_mode-instance_method" title="Concurrent::Agent#error_mode (method)">#error_mode</a></span> is <code>:fail</code>, returns the error object which caused the failure, else <code>nil</code>.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#failed%3F-instance_method" title="#failed? (instance method)">#<strong>failed?</strong> ⇒ Boolean </a>
(also: #stopped?)
</span>
<span class="summary_desc"><div class='inline'><p>Is the Agent in a failed state?.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#initialize-instance_method" title="#initialize (instance method)">#<strong>initialize</strong>(initial, opts = {}) ⇒ Agent </a>
</span>
<span class="note title constructor">constructor</span>
<span class="summary_desc"><div class='inline'><p>Create a new <code>Agent</code> with the given initial value and options.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#restart-instance_method" title="#restart (instance method)">#<strong>restart</strong>(new_value, opts = {}) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>When an Agent is <span class='object_link'><a href="#failed%3F-instance_method" title="Concurrent::Agent#failed? (method)">#failed?</a></span>, changes the Agent <span class='object_link'><a href="#value-instance_method" title="Concurrent::Agent#value (method)">#value</a></span> to <code>new_value</code> then un-fails the Agent so that action dispatches are allowed again.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#send-instance_method" title="#send (instance method)">#<strong>send</strong>(*args, &action) {|agent, value, *args| ... } ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#send!-instance_method" title="#send! (instance method)">#<strong>send!</strong>(*args, &action) {|agent, value, *args| ... } ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#send_off-instance_method" title="#send_off (instance method)">#<strong>send_off</strong>(*args, &action) {|agent, value, *args| ... } ⇒ Boolean </a>
(also: #post)
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#send_off!-instance_method" title="#send_off! (instance method)">#<strong>send_off!</strong>(*args, &action) {|agent, value, *args| ... } ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#send_via-instance_method" title="#send_via (instance method)">#<strong>send_via</strong>(executor, *args, &action) {|agent, value, *args| ... } ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#send_via!-instance_method" title="#send_via! (instance method)">#<strong>send_via!</strong>(executor, *args, &action) {|agent, value, *args| ... } ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Dispatches an action to the Agent and returns immediately.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#value-instance_method" title="#value (instance method)">#<strong>value</strong> ⇒ Object </a>
(also: #deref)
</span>
<span class="summary_desc"><div class='inline'><p>The current value (state) of the Agent, irrespective of any pending or in-progress actions.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#wait-instance_method" title="#wait (instance method)">#<strong>wait</strong>(timeout = nil) ⇒ Boolean </a>
</span>
<span class="summary_desc"><div class='inline'><p>Blocks the current thread until all actions dispatched thus far, from this thread or nested by the Agent, have occurred, or the timeout (in seconds) has elapsed.</p>
</div></span>
</li>
<li class="public ">
<span class="summary_signature">
<a href="#with_observer-instance_method" title="#with_observer (instance method)">#<strong>with_observer</strong>(observer = nil, func = :update, &block) ⇒ Observable </a>
</span>
<span class="note title not_defined_here">
included
from <span class='object_link'><a href="Concern/Observable.html#with_observer-instance_method" title="Concurrent::Concern::Observable#with_observer (method)">Concern::Observable</a></span>
</span>
<span class="summary_desc"><div class='inline'><p>As <code>#add_observer</code> but can be used for chaining.</p>
</div></span>
</li>
</ul>
<div id="constructor_details" class="method_details_list">
<h2>Constructor Details</h2>
<div class="method_details first">
<h3 class="signature first" id="initialize-instance_method">
#<strong>initialize</strong>(initial, opts = {}) ⇒ <tt><span class='object_link'><a href="" title="Concurrent::Agent (class)">Agent</a></span></tt>
</h3><div class="docstring">
<div class="discussion">
<p>Create a new <code>Agent</code> with the given initial value and options.</p>
<p>The <code>:validator</code> option must be <code>nil</code> or a side-effect free proc/lambda
which takes one argument. On any intended value change the validator, if
provided, will be called. If the new value is invalid the validator should
return <code>false</code> or raise an error.</p>
<p>The <code>:error_handler</code> option must be <code>nil</code> or a proc/lambda which takes two
arguments. When an action raises an error or validation fails, either by
returning false or raising an error, the error handler will be called. The
arguments to the error handler will be a reference to the agent itself and
the error object which was raised.</p>
<p>The <code>:error_mode</code> may be either <code>:continue</code> (the default if an error
handler is given) or <code>:fail</code> (the default if error handler nil or not
given).</p>
<p>If an action being run by the agent throws an error or doesn't pass
validation the error handler, if present, will be called. After the
handler executes if the error mode is <code>:continue</code> the Agent will continue
as if neither the action that caused the error nor the error itself ever
happened.</p>
<p>If the mode is <code>:fail</code> the Agent will become <span class='object_link'><a href="#failed%3F-instance_method" title="Concurrent::Agent#failed? (method)">#failed?</a></span> and will stop
accepting new action dispatches. Any previously queued actions will be
held until <span class='object_link'><a href="#restart-instance_method" title="Concurrent::Agent#restart (method)">#restart</a></span> is called. The <span class='object_link'><a href="#value-instance_method" title="Concurrent::Agent#value (method)">#value</a></span> method will still work,
returning the value of the Agent before the error.</p>
</div>
</div>
<div class="tags">
<p class="tag_title">Parameters:</p>
<ul class="param">
<li>
<span class='name'>initial</span>