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  <h1>Source code for cassandra.timestamps</h1><div class="highlight"><pre>
<span></span><span class="c1"># Copyright DataStax, Inc.</span>
<span class="c1">#</span>
<span class="c1"># Licensed under the Apache License, Version 2.0 (the &quot;License&quot;);</span>
<span class="c1"># you may not use this file except in compliance with the License.</span>
<span class="c1"># You may obtain a copy of the License at</span>
<span class="c1">#</span>
<span class="c1"># http://www.apache.org/licenses/LICENSE-2.0</span>
<span class="c1">#</span>
<span class="c1"># Unless required by applicable law or agreed to in writing, software</span>
<span class="c1"># distributed under the License is distributed on an &quot;AS IS&quot; BASIS,</span>
<span class="c1"># WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.</span>
<span class="c1"># See the License for the specific language governing permissions and</span>
<span class="c1"># limitations under the License.</span>

<span class="sd">&quot;&quot;&quot;</span>
<span class="sd">This module contains utilities for generating timestamps for client-side</span>
<span class="sd">timestamp specification.</span>
<span class="sd">&quot;&quot;&quot;</span>

<span class="kn">import</span> <span class="nn">logging</span>
<span class="kn">import</span> <span class="nn">time</span>
<span class="kn">from</span> <span class="nn">threading</span> <span class="k">import</span> <span class="n">Lock</span>

<span class="n">log</span> <span class="o">=</span> <span class="n">logging</span><span class="o">.</span><span class="n">getLogger</span><span class="p">(</span><span class="vm">__name__</span><span class="p">)</span>

<div class="viewcode-block" id="MonotonicTimestampGenerator"><a class="viewcode-back" href="../../api/cassandra/timestamps.html#cassandra.timestamps.MonotonicTimestampGenerator">[docs]</a><span class="k">class</span> <span class="nc">MonotonicTimestampGenerator</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
    <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">    An object that, when called, returns ``int(time.time() * 1e6)`` when</span>
<span class="sd">    possible, but, if the value returned by ``time.time`` doesn&#39;t increase,</span>
<span class="sd">    drifts into the future and logs warnings.</span>
<span class="sd">    Exposed configuration attributes can be configured with arguments to</span>
<span class="sd">    ``__init__`` or by changing attributes on an initialized object.</span>

<span class="sd">    .. versionadded:: 3.8.0</span>
<span class="sd">    &quot;&quot;&quot;</span>

    <span class="n">warn_on_drift</span> <span class="o">=</span> <span class="kc">True</span>
    <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">    If true, log warnings when timestamps drift into the future as allowed by</span>
<span class="sd">    :attr:`warning_threshold` and :attr:`warning_interval`.</span>
<span class="sd">    &quot;&quot;&quot;</span>

    <span class="n">warning_threshold</span> <span class="o">=</span> <span class="mi">1</span>
    <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">    This object will only issue warnings when the returned timestamp drifts</span>
<span class="sd">    more than ``warning_threshold`` seconds into the future.</span>
<span class="sd">    Defaults to 1 second.</span>
<span class="sd">    &quot;&quot;&quot;</span>

    <span class="n">warning_interval</span> <span class="o">=</span> <span class="mi">1</span>
    <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">    This object will only issue warnings every ``warning_interval`` seconds.</span>
<span class="sd">    Defaults to 1 second.</span>
<span class="sd">    &quot;&quot;&quot;</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">warn_on_drift</span><span class="o">=</span><span class="kc">True</span><span class="p">,</span> <span class="n">warning_threshold</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">warning_interval</span><span class="o">=</span><span class="mi">1</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lock</span> <span class="o">=</span> <span class="n">Lock</span><span class="p">()</span>
        <span class="k">with</span> <span class="bp">self</span><span class="o">.</span><span class="n">lock</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">last</span> <span class="o">=</span> <span class="mi">0</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">_last_warn</span> <span class="o">=</span> <span class="mi">0</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">warn_on_drift</span> <span class="o">=</span> <span class="n">warn_on_drift</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">warning_threshold</span> <span class="o">=</span> <span class="n">warning_threshold</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">warning_interval</span> <span class="o">=</span> <span class="n">warning_interval</span>

<div class="viewcode-block" id="MonotonicTimestampGenerator._next_timestamp"><a class="viewcode-back" href="../../api/cassandra/timestamps.html#cassandra.timestamps.MonotonicTimestampGenerator._next_timestamp">[docs]</a>    <span class="k">def</span> <span class="nf">_next_timestamp</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">now</span><span class="p">,</span> <span class="n">last</span><span class="p">):</span>
        <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        Returns the timestamp that should be used if ``now`` is the current</span>
<span class="sd">        time and ``last`` is the last timestamp returned by this object.</span>
<span class="sd">        Intended for internal and testing use only; to generate timestamps,</span>
<span class="sd">        call an instantiated ``MonotonicTimestampGenerator`` object.</span>

<span class="sd">        :param int now: an integer to be used as the current time, typically</span>
<span class="sd">            representing the current time in microseconds since the UNIX epoch</span>
<span class="sd">        :param int last: an integer representing the last timestamp returned by</span>
<span class="sd">            this object</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="k">if</span> <span class="n">now</span> <span class="o">&gt;</span> <span class="n">last</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">last</span> <span class="o">=</span> <span class="n">now</span>
            <span class="k">return</span> <span class="n">now</span>
        <span class="k">else</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">_maybe_warn</span><span class="p">(</span><span class="n">now</span><span class="o">=</span><span class="n">now</span><span class="p">)</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">last</span> <span class="o">=</span> <span class="n">last</span> <span class="o">+</span> <span class="mi">1</span>
            <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">last</span></div>

    <span class="k">def</span> <span class="nf">__call__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="sd">&quot;&quot;&quot;</span>
<span class="sd">        Makes ``MonotonicTimestampGenerator`` objects callable; defers</span>
<span class="sd">        internally to _next_timestamp.</span>
<span class="sd">        &quot;&quot;&quot;</span>
        <span class="k">with</span> <span class="bp">self</span><span class="o">.</span><span class="n">lock</span><span class="p">:</span>
            <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">_next_timestamp</span><span class="p">(</span><span class="n">now</span><span class="o">=</span><span class="nb">int</span><span class="p">(</span><span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">()</span> <span class="o">*</span> <span class="mf">1e6</span><span class="p">),</span>
                                        <span class="n">last</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">last</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">_maybe_warn</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">now</span><span class="p">):</span>
        <span class="c1"># should be called from inside the self.lock.</span>
        <span class="n">diff</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">last</span> <span class="o">-</span> <span class="n">now</span>
        <span class="n">since_last_warn</span> <span class="o">=</span> <span class="n">now</span> <span class="o">-</span> <span class="bp">self</span><span class="o">.</span><span class="n">_last_warn</span>

        <span class="n">warn</span> <span class="o">=</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">warn_on_drift</span> <span class="ow">and</span>
                <span class="p">(</span><span class="n">diff</span> <span class="o">&gt;=</span> <span class="bp">self</span><span class="o">.</span><span class="n">warning_threshold</span> <span class="o">*</span> <span class="mf">1e6</span><span class="p">)</span> <span class="ow">and</span>
                <span class="p">(</span><span class="n">since_last_warn</span> <span class="o">&gt;=</span> <span class="bp">self</span><span class="o">.</span><span class="n">warning_interval</span> <span class="o">*</span> <span class="mf">1e6</span><span class="p">))</span>
        <span class="k">if</span> <span class="n">warn</span><span class="p">:</span>
            <span class="n">log</span><span class="o">.</span><span class="n">warning</span><span class="p">(</span>
                <span class="s2">&quot;Clock skew detected: current tick (</span><span class="si">{now}</span><span class="s2">) was </span><span class="si">{diff}</span><span class="s2"> &quot;</span>
                <span class="s2">&quot;microseconds behind the last generated timestamp &quot;</span>
                <span class="s2">&quot;(</span><span class="si">{last}</span><span class="s2">), returned timestamps will be artificially &quot;</span>
                <span class="s2">&quot;incremented to guarantee monotonicity.&quot;</span><span class="o">.</span><span class="n">format</span><span class="p">(</span>
                    <span class="n">now</span><span class="o">=</span><span class="n">now</span><span class="p">,</span> <span class="n">diff</span><span class="o">=</span><span class="n">diff</span><span class="p">,</span> <span class="n">last</span><span class="o">=</span><span class="bp">self</span><span class="o">.</span><span class="n">last</span><span class="p">))</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">_last_warn</span> <span class="o">=</span> <span class="n">now</span></div>
</pre></div>

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