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  <h1>Source code for postgresql.alock</h1><div class="highlight"><pre>
<span class="c1">##</span>
<span class="c1"># .alock - Advisory Locks</span>
<span class="c1">##</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">Tools for Advisory Locks</span>
<span class="sd">&quot;&quot;&quot;</span>
<span class="kn">from</span> <span class="nn">abc</span> <span class="kn">import</span> <span class="n">abstractmethod</span><span class="p">,</span> <span class="n">abstractproperty</span>
<span class="kn">from</span> <span class="nn">.python.element</span> <span class="kn">import</span> <span class="n">Element</span>

<span class="n">__all__</span> <span class="o">=</span> <span class="p">[</span>
	<span class="s1">&#39;ALock&#39;</span><span class="p">,</span>
	<span class="s1">&#39;ExclusiveLock&#39;</span><span class="p">,</span>
	<span class="s1">&#39;ShareLock&#39;</span><span class="p">,</span>
<span class="p">]</span>

<div class="viewcode-block" id="ALock"><a class="viewcode-back" href="../../reference.html#postgresql.alock.ALock">[docs]</a><span class="k">class</span> <span class="nc">ALock</span><span class="p">(</span><span class="n">Element</span><span class="p">):</span>
	<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">	Advisory Lock class for managing the acquisition and release of a sequence</span>
<span class="sd">	of PostgreSQL advisory locks.</span>

<span class="sd">	ALock()&#39;s are fairly consistent with threading.RLock()&#39;s. They can be</span>
<span class="sd">	acquired multiple times, and they must be released the same number of times</span>
<span class="sd">	for the lock to actually be released.</span>

<span class="sd">	A notably difference is that ALock&#39;s manage a sequence of lock identifiers.</span>
<span class="sd">	This means that a given ALock() may represent multiple advisory locks.</span>
<span class="sd">	&quot;&quot;&quot;</span>
	<span class="n">_e_factors</span> <span class="o">=</span> <span class="p">(</span><span class="s1">&#39;database&#39;</span><span class="p">,</span> <span class="s1">&#39;identifiers&#39;</span><span class="p">,)</span>
	<span class="n">_e_label</span> <span class="o">=</span> <span class="s1">&#39;ALOCK&#39;</span>
	<span class="k">def</span> <span class="nf">_e_metas</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span>
		<span class="n">headfmt</span> <span class="o">=</span> <span class="s2">&quot;{1} [{0}]&quot;</span><span class="o">.</span><span class="n">format</span>
	<span class="p">):</span>
		<span class="k">yield</span> <span class="bp">None</span><span class="p">,</span> <span class="n">headfmt</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">state</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">mode</span><span class="p">)</span>

	<span class="nd">@abstractproperty</span>
	<span class="k">def</span> <span class="nf">mode</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">		The mode of the lock class.</span>
<span class="sd">		&quot;&quot;&quot;</span>

	<span class="nd">@abstractproperty</span>
	<span class="k">def</span> <span class="nf">__select_statements__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">		Implemented by subclasses to return the statements to try, acquire, and</span>
<span class="sd">		release the advisory lock.</span>

<span class="sd">		Returns a triple of callables where each callable takes two arguments,</span>
<span class="sd">		the lock-id pairs, and then the int8 lock-ids.</span>
<span class="sd">		``(try, acquire, release)``.</span>
<span class="sd">		&quot;&quot;&quot;</span>

	<span class="nd">@staticmethod</span>
	<span class="k">def</span> <span class="nf">_split_lock_identifiers</span><span class="p">(</span><span class="n">idseq</span><span class="p">):</span>
		<span class="c1"># lame O(2)</span>
		<span class="n">id_pairs</span> <span class="o">=</span> <span class="p">[</span>
			<span class="nb">list</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">if</span> <span class="n">x</span><span class="o">.</span><span class="n">__class__</span> <span class="ow">is</span> <span class="ow">not</span> <span class="nb">int</span> <span class="k">else</span> <span class="p">[</span><span class="bp">None</span><span class="p">,</span><span class="bp">None</span><span class="p">]</span>
			<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">idseq</span>
		<span class="p">]</span>
		<span class="n">ids</span> <span class="o">=</span> <span class="p">[</span>
			<span class="n">x</span> <span class="k">if</span> <span class="n">x</span><span class="o">.</span><span class="n">__class__</span> <span class="ow">is</span> <span class="nb">int</span> <span class="k">else</span> <span class="bp">None</span>
			<span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">idseq</span>
		<span class="p">]</span>
		<span class="k">return</span> <span class="p">(</span><span class="n">id_pairs</span><span class="p">,</span> <span class="n">ids</span><span class="p">)</span>

<div class="viewcode-block" id="ALock.acquire"><a class="viewcode-back" href="../../reference.html#postgresql.alock.ALock.acquire">[docs]</a>	<span class="k">def</span> <span class="nf">acquire</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">blocking</span> <span class="o">=</span> <span class="bp">True</span><span class="p">,</span> <span class="nb">len</span> <span class="o">=</span> <span class="nb">len</span><span class="p">):</span>
		<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">		Acquire the locks using the configured identifiers.</span>
<span class="sd">		&quot;&quot;&quot;</span>
		<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">==</span> <span class="mi">0</span><span class="p">:</span>
			<span class="c1"># _count is zero, so the locks need to be acquired.</span>
			<span class="n">wait</span> <span class="o">=</span> <span class="nb">bool</span><span class="p">(</span><span class="n">blocking</span><span class="p">)</span>
			<span class="k">if</span> <span class="n">wait</span><span class="p">:</span>
				<span class="bp">self</span><span class="o">.</span><span class="n">_acquire</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_id_pairs</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_ids</span><span class="p">)</span>
			<span class="k">else</span><span class="p">:</span>
				<span class="c1"># grab the success of each lock id. if some were</span>
				<span class="c1"># unsuccessful, then the ones that were successful need to be</span>
				<span class="c1"># released.</span>
				<span class="n">r</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_try</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_id_pairs</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_ids</span><span class="p">)</span>
				<span class="c1"># accumulate the identifiers that *did* lock</span>
				<span class="n">release_seq</span> <span class="o">=</span> <span class="p">[</span>
					<span class="nb">id</span> <span class="k">for</span> <span class="n">didlock</span><span class="p">,</span> <span class="nb">id</span> <span class="ow">in</span> <span class="nb">zip</span><span class="p">(</span><span class="n">r</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">identifiers</span><span class="p">)</span> <span class="k">if</span> <span class="n">didlock</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span>
				<span class="p">]</span>
				<span class="k">if</span> <span class="nb">len</span><span class="p">(</span><span class="n">release_seq</span><span class="p">)</span> <span class="o">!=</span> <span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">identifiers</span><span class="p">):</span>
					<span class="c1"># some failed, so release the acquired and return False</span>
					<span class="c1">#</span>
					<span class="c1"># reverse in case there is another waiting for all.</span>
					<span class="c1"># that is, release last-to-first so that if another is waiting</span>
					<span class="c1"># on the same seq that it should be able to acquire all of</span>
					<span class="c1"># them once the contended lock is released.</span>
					<span class="n">release_seq</span><span class="o">.</span><span class="n">reverse</span><span class="p">()</span>
					<span class="bp">self</span><span class="o">.</span><span class="n">_release</span><span class="p">(</span><span class="o">*</span><span class="bp">self</span><span class="o">.</span><span class="n">_split_lock_identifiers</span><span class="p">(</span><span class="n">release_seq</span><span class="p">))</span>
					<span class="c1"># unable to acquire all.</span>
					<span class="k">return</span> <span class="bp">False</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">+</span> <span class="mi">1</span>
		<span class="k">return</span> <span class="bp">True</span></div>

	<span class="k">def</span> <span class="nf">__enter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">acquire</span><span class="p">()</span>
		<span class="k">return</span> <span class="bp">self</span>

<div class="viewcode-block" id="ALock.release"><a class="viewcode-back" href="../../reference.html#postgresql.alock.ALock.release">[docs]</a>	<span class="k">def</span> <span class="nf">release</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">		Release the locks using the configured identifiers.</span>
<span class="sd">		&quot;&quot;&quot;</span>
		<span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">&lt;</span> <span class="mi">1</span><span class="p">:</span>
			<span class="k">raise</span> <span class="ne">RuntimeError</span><span class="p">(</span><span class="s2">&quot;cannot release un-acquired lock&quot;</span><span class="p">)</span>
		<span class="k">if</span> <span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">closed</span> <span class="ow">and</span> <span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">&gt;</span> <span class="mi">0</span><span class="p">:</span>
			<span class="c1"># if the database has been closed, or the count will</span>
			<span class="c1"># remain non-zero, there is no need to release.</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">_release</span><span class="p">(</span><span class="nb">reversed</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_id_pairs</span><span class="p">),</span> <span class="nb">reversed</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_ids</span><span class="p">))</span>
			<span class="c1"># decrement the count nonetheless.</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">-</span> <span class="mi">1</span></div>

	<span class="k">def</span> <span class="nf">__exit__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">typ</span><span class="p">,</span> <span class="n">val</span><span class="p">,</span> <span class="n">tb</span><span class="p">):</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">release</span><span class="p">()</span>

<div class="viewcode-block" id="ALock.locked"><a class="viewcode-back" href="../../reference.html#postgresql.alock.ALock.locked">[docs]</a>	<span class="k">def</span> <span class="nf">locked</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">		Whether the locks have been acquired. This method is sensitive to the</span>
<span class="sd">		connection&#39;s state. If the connection is closed, it will return False.</span>
<span class="sd">		&quot;&quot;&quot;</span>
		<span class="k">return</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">&gt;</span> <span class="mi">0</span><span class="p">)</span> <span class="ow">and</span> <span class="p">(</span><span class="ow">not</span> <span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">closed</span><span class="p">)</span></div>

	<span class="nd">@property</span>
	<span class="k">def</span> <span class="nf">state</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="k">return</span> <span class="s1">&#39;locked&#39;</span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="n">locked</span><span class="p">()</span> <span class="k">else</span> <span class="s1">&#39;unlocked&#39;</span>

	<span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">database</span><span class="p">,</span> <span class="o">*</span><span class="n">identifiers</span><span class="p">):</span>
		<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">		Initialize the lock object to manage a sequence of advisory locks</span>
<span class="sd">		for use with the given database.</span>
<span class="sd">		&quot;&quot;&quot;</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">_count</span> <span class="o">=</span> <span class="mi">0</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">connection</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">database</span> <span class="o">=</span> <span class="n">database</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">identifiers</span> <span class="o">=</span> <span class="n">identifiers</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">_id_pairs</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_ids</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">_split_lock_identifiers</span><span class="p">(</span><span class="n">identifiers</span><span class="p">)</span>
		<span class="bp">self</span><span class="o">.</span><span class="n">_try</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_acquire</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_release</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">__select_statements__</span><span class="p">()</span></div>

<span class="k">class</span> <span class="nc">ShareLock</span><span class="p">(</span><span class="n">ALock</span><span class="p">):</span>
	<span class="n">mode</span> <span class="o">=</span> <span class="s1">&#39;share&#39;</span>

	<span class="k">def</span> <span class="nf">__select_statements__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="k">return</span> <span class="p">(</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">sys</span><span class="o">.</span><span class="n">try_advisory_shared</span><span class="p">,</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">sys</span><span class="o">.</span><span class="n">acquire_advisory_shared</span><span class="p">,</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">sys</span><span class="o">.</span><span class="n">release_advisory_shared</span><span class="p">,</span>
		<span class="p">)</span>

<span class="k">class</span> <span class="nc">ExclusiveLock</span><span class="p">(</span><span class="n">ALock</span><span class="p">):</span>
	<span class="n">mode</span> <span class="o">=</span> <span class="s1">&#39;exclusive&#39;</span>

	<span class="k">def</span> <span class="nf">__select_statements__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
		<span class="k">return</span> <span class="p">(</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">sys</span><span class="o">.</span><span class="n">try_advisory_exclusive</span><span class="p">,</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">sys</span><span class="o">.</span><span class="n">acquire_advisory_exclusive</span><span class="p">,</span>
			<span class="bp">self</span><span class="o">.</span><span class="n">database</span><span class="o">.</span><span class="n">sys</span><span class="o">.</span><span class="n">release_advisory_exclusive</span><span class="p">,</span>
		<span class="p">)</span>
</pre></div>

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