想控制子進程優先級？看看PHP 中怎麼用proc_nice 實現

gitbox 2025-08-26

在高並發或批處理場景裡，我們常常不希望某些後台任務“吃滿”CPU，影響對外服務的響應。操作系統已經提供了調整當前進程的優先級；若要控制子進程，可以在fork 的子進程裡調用它，或結合proc_open()與posix_setpriority()針對特定PID 調整。本文給出實戰範式、坑點與排障建議。

小抄：在類Unix 系統上，nice 取值範圍通常是-20（最高優先級）到19（最低） ，默認是0。
普通用戶只能增大niceness（降低優先級） ，例如從0 → 10。
將優先級提高到負值（如-5）通常需要root 能力或CAP_SYS_NICE 。

場景一： pcntl_fork()後在子進程裡“降權跑”

當你用pcntl_fork()派生子進程時，在子進程調用proc_nice()最直接。示例：父進程負責接活，子進程做重活但降優先級，避免拖慢整體。

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-keyword">declare</span></span><span>(strict_types=</span><span><span class="hljs-number">1</span></span><span>);

</span><span><span class="hljs-comment">// 確保擴展已啟用：pcntl、posix（可選）</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">function_exists</span></span><span>(</span><span><span class="hljs-string">'pcntl_fork'</span></span><span>)) {
    </span><span><span class="hljs-title function_ invoke__">fwrite</span></span><span>(STDERR, </span><span><span class="hljs-string">"pcntl 未啟用，無法演示\n"</span></span><span>);
    </span><span><span class="hljs-keyword">exit</span></span><span>(</span><span><span class="hljs-number">1</span></span><span>);
}

</span><span><span class="hljs-variable">$pid</span></span><span> = </span><span><span class="hljs-title function_ invoke__">pcntl_fork</span></span><span>();
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$pid</span></span><span> === -</span><span><span class="hljs-number">1</span></span><span>) {
    </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'fork 失敗'</span></span><span>);
}

</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$pid</span></span><span> === </span><span><span class="hljs-number">0</span></span><span>) {
    </span><span><span class="hljs-comment">// --- 子進程 ---</span></span><span>
    </span><span><span class="hljs-comment">// 將 niceness 從默認 0 調整為 10（更“友好”，更低優先級）</span></span><span>
    </span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">proc_nice</span></span><span>(</span><span><span class="hljs-number">10</span></span><span>)) {
        </span><span><span class="hljs-comment">// 失敗通常意味着權限不足或平台不支持</span></span><span>
        </span><span><span class="hljs-title function_ invoke__">fwrite</span></span><span>(STDERR, </span><span><span class="hljs-string">"[child] proc_nice 失敗\n"</span></span><span>);
    }

    </span><span><span class="hljs-comment">// 模擬 CPU 密集型工作</span></span><span>
    </span><span><span class="hljs-variable">$sum</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>;
    </span><span><span class="hljs-keyword">for</span></span><span> (</span><span><span class="hljs-variable">$i</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>; </span><span><span class="hljs-variable">$i</span></span><span> &lt; </span><span><span class="hljs-number">5_000_000</span></span><span>; </span><span><span class="hljs-variable">$i</span></span><span>++) {
        </span><span><span class="hljs-variable">$sum</span></span><span> += </span><span><span class="hljs-variable">$i</span></span><span>;
    }
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"[child] done, sum=<span class="hljs-subst">{$sum}</span></span></span><span>\n";
    </span><span><span class="hljs-keyword">exit</span></span><span>(</span><span><span class="hljs-number">0</span></span><span>);
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-comment">// --- 父進程 ---</span></span><span>
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"[parent] fork 出子進程 PID=<span class="hljs-subst">{$pid}</span></span></span><span>\n";
    </span><span><span class="hljs-comment">// 父進程继续高优先级工作（例如響應 HTTP 請求）</span></span><span>
    </span><span><span class="hljs-comment">// 等待子進程结束（生产环境可選择不阻塞，或用信號/回調）</span></span><span>
    </span><span><span class="hljs-title function_ invoke__">pcntl_wait</span></span><span>(</span><span><span class="hljs-variable">$status</span></span><span>);
    </span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"[parent] child exit code = "</span></span><span> . </span><span><span class="hljs-title function_ invoke__">pcntl_wexitstatus</span></span><span>(</span><span><span class="hljs-variable">$status</span></span><span>) . </span><span><span class="hljs-string">"\n"</span></span><span>;
}
</span></span>

要點

proc_nice()影響的是當前進程，因此要在子進程代碼路徑裡調用。
調整為正值（如10）通常不需要特權；設置負值可能失敗。
如果只是“讓子任務別搶資源”，把它設為10~15往往已經足夠。

場景二： proc_open()啟動外部命令並調整它的優先級

若你不是用fork ，而是通過proc_open()啟動其他命令（如ffmpeg、convert、php 自己跑worker），你需要拿到PID 再調優先級。 proc_get_status()能取到子進程PID；隨後用posix_setpriority() （POSIX 擴展）對該PID 操作更直觀。

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-keyword">declare</span></span><span>(strict_types=</span><span><span class="hljs-number">1</span></span><span>);

</span><span><span class="hljs-variable">$descriptorSpec</span></span><span> = [
    </span><span><span class="hljs-number">0</span></span><span> =&gt; [</span><span><span class="hljs-string">'pipe'</span></span><span>, </span><span><span class="hljs-string">'r'</span></span><span>],
    </span><span><span class="hljs-number">1</span></span><span> =&gt; [</span><span><span class="hljs-string">'pipe'</span></span><span>, </span><span><span class="hljs-string">'w'</span></span><span>],
    </span><span><span class="hljs-number">2</span></span><span> =&gt; [</span><span><span class="hljs-string">'pipe'</span></span><span>, </span><span><span class="hljs-string">'w'</span></span><span>],
];

</span><span><span class="hljs-comment">// 舉例：跑一個 CPU 密集的 PHP 兒童腳本</span></span><span>
</span><span><span class="hljs-variable">$process</span></span><span> = </span><span><span class="hljs-title function_ invoke__">proc_open</span></span><span>(</span><span><span class="hljs-string">'php -r "usleep(3000000);"'</span></span><span>, </span><span><span class="hljs-variable">$descriptorSpec</span></span><span>, </span><span><span class="hljs-variable">$pipes</span></span><span>);
</span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-title function_ invoke__">is_resource</span></span><span>(</span><span><span class="hljs-variable">$process</span></span><span>)) {
    </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">RuntimeException</span></span><span>(</span><span><span class="hljs-string">'proc_open 启动失敗'</span></span><span>);
}

</span><span><span class="hljs-variable">$status</span></span><span> = </span><span><span class="hljs-title function_ invoke__">proc_get_status</span></span><span>(</span><span><span class="hljs-variable">$process</span></span><span>);
</span><span><span class="hljs-variable">$pid</span></span><span>    = </span><span><span class="hljs-variable">$status</span></span><span>[</span><span><span class="hljs-string">'pid'</span></span><span>] ?? </span><span><span class="hljs-literal">null</span></span><span>;
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"child pid = <span class="hljs-subst">{$pid}</span></span></span><span>\n";

</span><span><span class="hljs-comment">// POSIX 方式：直接對 PID 設定 nice（範圍 -20~19）</span></span><span>
</span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">function_exists</span></span><span>(</span><span><span class="hljs-string">'posix_setpriority'</span></span><span>) &amp;&amp; </span><span><span class="hljs-variable">$pid</span></span><span>) {
    </span><span><span class="hljs-comment">// 將子進程调为 10（更低優先級）</span></span><span>
    </span><span><span class="hljs-variable">$ok</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">posix_setpriority</span></span><span>(</span><span><span class="hljs-number">10</span></span><span>, </span><span><span class="hljs-variable">$pid</span></span><span>, POSIX_PRIO_PROCESS);
    </span><span><span class="hljs-keyword">if</span></span><span> (!</span><span><span class="hljs-variable">$ok</span></span><span>) {
        </span><span><span class="hljs-title function_ invoke__">fwrite</span></span><span>(STDERR, </span><span><span class="hljs-string">"posix_setpriority 失敗（權限/平台/目標進程狀態）\n"</span></span><span>);
    }
} </span><span><span class="hljs-keyword">else</span></span><span> {
    </span><span><span class="hljs-comment">// 方案 B：使用外部命令 renice（Linux/Unix）</span></span><span>
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$pid</span></span><span>) {
        </span><span><span class="hljs-comment">// 注意：在某些環境可能需要 sudo 或特權</span></span><span>
        @</span><span><span class="hljs-title function_ invoke__">shell_exec</span></span><span>(</span><span><span class="hljs-title function_ invoke__">sprintf</span></span><span>(</span><span><span class="hljs-string">'renice +10 -p %d 2&gt;/dev/null'</span></span><span>, </span><span><span class="hljs-variable">$pid</span></span><span>));
    }
}

</span><span><span class="hljs-comment">// 清理</span></span><span>
</span><span><span class="hljs-title function_ invoke__">fclose</span></span><span>(</span><span><span class="hljs-variable">$pipes</span></span><span>[</span><span><span class="hljs-number">0</span></span><span>]); </span><span><span class="hljs-title function_ invoke__">fclose</span></span><span>(</span><span><span class="hljs-variable">$pipes</span></span><span>[</span><span><span class="hljs-number">1</span></span><span>]); </span><span><span class="hljs-title function_ invoke__">fclose</span></span><span>(</span><span><span class="hljs-variable">$pipes</span></span><span>[</span><span><span class="hljs-number">2</span></span><span>]);
</span><span><span class="hljs-variable">$exitCode</span></span><span> = </span><span><span class="hljs-title function_ invoke__">proc_close</span></span><span>(</span><span><span class="hljs-variable">$process</span></span><span>);
</span><span><span class="hljs-keyword">echo</span></span><span> </span><span><span class="hljs-string">"child exit code = <span class="hljs-subst">{$exitCode}</span></span></span><span>\n";
</span></span>

要點

proc_open()返回的是句柄，並不會自動調整優先級。你需要獲取PID 後手動處理。
posix_setpriority()比調用renice更可控、跨發行版差異更小，但要求啟用posix 擴展。
若你在容器或非root 環境，只能提高niceness（降優先級） 。

場景三：直接用nice / ionice啟動（最快捷）

如果你不需要在PHP 裡微調，也可以在命令行級別直接低優先級啟動子進程：

 <span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-keyword">declare</span></span><span>(strict_types=</span><span><span class="hljs-number">1</span></span><span>);

</span><span><span class="hljs-comment">// CPU 友好：nice +10</span></span><span>
</span><span><span class="hljs-variable">$cmd</span></span><span> = </span><span><span class="hljs-string">'nice -n 10 php worker.php'</span></span><span>;

</span><span><span class="hljs-comment">// I/O 友好：ionice class 2（best-effort），level 7（最低）</span></span><span>
</span><span><span class="hljs-variable">$cmd</span></span><span> = </span><span><span class="hljs-string">'ionice -c 2 -n 7 nice -n 10 php worker.php'</span></span><span>;

</span><span><span class="hljs-variable">$proc</span></span><span> = </span><span><span class="hljs-title function_ invoke__">proc_open</span></span><span>(</span><span><span class="hljs-variable">$cmd</span></span><span>, [
    </span><span><span class="hljs-number">0</span></span><span> =&gt; [</span><span><span class="hljs-string">'pipe'</span></span><span>, </span><span><span class="hljs-string">'r'</span></span><span>],
    </span><span><span class="hljs-number">1</span></span><span> =&gt; [</span><span><span class="hljs-string">'pipe'</span></span><span>, </span><span><span class="hljs-string">'w'</span></span><span>],
    </span><span><span class="hljs-number">2</span></span><span> =&gt; [</span><span><span class="hljs-string">'pipe'</span></span><span>, </span><span><span class="hljs-string">'w'</span></span><span>],
], </span><span><span class="hljs-variable">$pipes</span></span><span>);

</span><span><span class="hljs-comment">// ... 省略與上文相同的清理邏輯</span></span><span>
</span></span>

提示

ionice只影響I/O 調度（磁盤），常與nice組合， CPU + I/O 雙限流更穩。
某些容器最小鏡像可能沒有ionice ，要在鏡像中安裝（如util-linux包）。

錯誤處理與可觀測性

檢測返回值與告警
- proc_nice()返回true/false ，失敗請記錄日誌並附帶posix_geteuid() 、目標值等上下文。
- posix_setpriority()同理，失敗常見於權限不足、 PID 已退出。
記錄實際優先級
- Linux 可讀取/proc/<pid>/stat的nice字段，或調用ps -o pid,ni,cmd -p <pid>驗證。
- 在PHP 中可以exec('ps -o pid,ni,cmd -p ' . (int)$pid, $out)並記錄結果。
分層限流
- 僅靠nice 對CPU 競爭有效；若還有並發量暴漲，請疊加隊列/令牌桶（如Redis + Lua）與進程數上限。

平台與權限細節

Linux/Unix ：本文方法適用。非特權用戶僅能增大niceness（變“更好說話”）。
容器/系統服務：若服務由systemd 管理，可在單元文件裡設Nice= ，或授予AmbientCapabilities=CAP_SYS_NICE 。容器可在運行參數里加--cap-add SYS_NICE 。
macOS ：語義類似Linux， renice和POSIX 接口可用。
Windows ： proc_nice()不可用/不生效（常見為返回失敗並觸發警告）。 Windows 的優先級應通過proc_open() + wmic /PowerShell或FFI 調WinAPI，屬於不同實現路徑，與本文不在同一套法則。

實戰建議（速記）

子進程內部： pcntl_fork() → 子進程proc_nice(10~15) 。
外部命令： proc_open() → proc_get_status()取PID → posix_setpriority($nice, $pid, POSIX_PRIO_PROCESS) 。
一把梭：命令前加nice -n <N> ，I/O 密集再疊ionice 。
權限：負值需要特權；容器裡考慮加SYS_NICE能力或退而求其次用正值。
驗證：用ps或讀取/proc校驗；記錄日誌便於回溯。

參考片段：封裝一個“給進程降優先級”的小工具函數

<span><span><span class="hljs-meta">&lt;?php</span></span><span>
</span><span><span class="hljs-keyword">declare</span></span><span>(strict_types=</span><span><span class="hljs-number">1</span></span><span>);

<span class="hljs-comment">/**
 * 將指定 PID 的進程 niceness 調整為目标值（預設 10）。
 * 返回 true 表示“看起來成功”（不保證最終生效，需結合 ps 驗證）。
 */</span>
</span><span><span class="hljs-function"><span class="hljs-keyword">function</span></span></span><span> </span><span><span class="hljs-title">lower_priority</span></span><span>(</span><span><span class="hljs-params"><span class="hljs-keyword">int</span></span></span><span> </span><span><span class="hljs-variable">$pid</span></span><span>, </span><span><span class="hljs-keyword">int</span></span><span> </span><span><span class="hljs-variable">$nice</span></span><span> = </span><span><span class="hljs-number">10</span></span><span>): </span><span><span class="hljs-title">bool</span></span><span>
{
    </span><span><span class="hljs-comment">// 邊界護欄</span></span><span>
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$nice</span></span><span> &lt; -</span><span><span class="hljs-number">20</span></span><span> || </span><span><span class="hljs-variable">$nice</span></span><span> &gt; </span><span><span class="hljs-number">19</span></span><span>) {
        </span><span><span class="hljs-keyword">throw</span></span><span> </span><span><span class="hljs-keyword">new</span></span><span> </span><span><span class="hljs-built_in">InvalidArgumentException</span></span><span>(</span><span><span class="hljs-string">'nice 必須在 -20..19 之間'</span></span><span>);
    }

    </span><span><span class="hljs-comment">// 首選 POSIX API</span></span><span>
    </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-title function_ invoke__">function_exists</span></span><span>(</span><span><span class="hljs-string">'posix_setpriority'</span></span><span>)) {
        </span><span><span class="hljs-variable">$ok</span></span><span> = @</span><span><span class="hljs-title function_ invoke__">posix_setpriority</span></span><span>(</span><span><span class="hljs-variable">$nice</span></span><span>, </span><span><span class="hljs-variable">$pid</span></span><span>, POSIX_PRIO_PROCESS);
        </span><span><span class="hljs-keyword">if</span></span><span> (</span><span><span class="hljs-variable">$ok</span></span><span>) {
            </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-literal">true</span></span><span>;
        }
    }

    </span><span><span class="hljs-comment">// 備選：renice（僅 *nix）</span></span><span>
    </span><span><span class="hljs-variable">$ret</span></span><span> = </span><span><span class="hljs-number">0</span></span><span>;
    @</span><span><span class="hljs-title function_ invoke__">exec</span></span><span>(</span><span><span class="hljs-title function_ invoke__">sprintf</span></span><span>(</span><span><span class="hljs-string">'renice %s%d -p %d 2&gt;/dev/null'</span></span><span>,
        </span><span><span class="hljs-variable">$nice</span></span><span> &gt;= </span><span><span class="hljs-number">0</span></span><span> ? </span><span><span class="hljs-string">'+'</span></span><span> : </span><span><span class="hljs-string">''</span></span><span>, </span><span><span class="hljs-variable">$nice</span></span><span>, </span><span><span class="hljs-variable">$pid</span></span><span>
    ), </span><span><span class="hljs-variable">$out</span></span><span>, </span><span><span class="hljs-variable">$ret</span></span><span>);

    </span><span><span class="hljs-keyword">return</span></span><span> </span><span><span class="hljs-variable">$ret</span></span><span> === </span><span><span class="hljs-number">0</span></span><span>;
}
</span></span>