Add parallel Xlsx writing via pcntl_fork

samples/Chart/32_Chart_read_write.php

@@ -6,7 +6,6 @@
 /** @var PhpOffice\PhpSpreadsheet\Helper\Sample $helper */
 $inputFileType = 'Xlsx';
 $inputFileNames = __DIR__ . '/../templates/32readwrite*[0-9].xlsx';
-
 if ((isset($argc)) && ($argc > 1)) {
     $inputFileNames = [];
     for ($i = 1; $i < $argc; ++$i) {

samples/Chart/32_Chart_read_write_HTML.php

@@ -12,7 +12,6 @@
 
 $inputFileType = 'Xlsx';
 $inputFileNames = __DIR__ . '/../templates/36write*.xlsx';
-
 if ((isset($argc)) && ($argc > 1)) {
     $inputFileNames = [];
     for ($i = 1; $i < $argc; ++$i) {

samples/Chart/32_Chart_read_write_PDF.php

@@ -13,7 +13,6 @@
 
 $inputFileType = 'Xlsx';
 $inputFileNames = __DIR__ . '/../templates/36write*.xlsx';
-
 if ((isset($argc)) && ($argc > 1)) {
     $inputFileNames = [];
     for ($i = 1; $i < $argc; ++$i) {

samples/Chart/35_Chart_render.php

@@ -13,7 +13,6 @@
 $inputFileType = 'Xlsx';
 $inputFileNames = __DIR__ . '/../templates/32readwrite*[0-9].xlsx';
 //$inputFileNames = __DIR__ . '/../templates/32readwriteStockChart5.xlsx';
-
 if ((isset($argc)) && ($argc > 1)) {
     $inputFileNames = [];
     for ($i = 1; $i < $argc; ++$i) {

samples/Chart/35_Chart_render33.php

@@ -12,7 +12,6 @@
 
 $inputFileType = 'Xlsx';
 $inputFileNamesString = $helper->getTemporaryFolder() . '/33_Chart_create_*.xlsx';
-
 if ((isset($argc)) && ($argc > 1)) {
     $inputFileNames = [];
     for ($i = 1; $i < $argc; ++$i) {

samples/ParallelBenchmark.php

@@ -0,0 +1,88 @@
+<?php
+
+/**
+ * Benchmark: Sequential vs Parallel Xlsx Writing.
+ *
+ * Usage:
+ *   php samples/ParallelBenchmark.php [sheets] [rows]
+ *
+ * Examples:
+ *   php samples/ParallelBenchmark.php          # 5 sheets, 5000 rows each
+ *   php samples/ParallelBenchmark.php 10 10000 # 10 sheets, 10000 rows each
+ */
+
+use PhpOffice\PhpSpreadsheet\Parallel\Backend\PcntlBackend;
+use PhpOffice\PhpSpreadsheet\Parallel\CpuDetector;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+$sheetCount = (int) ($argv[1] ?? 5);
+$rowCount = (int) ($argv[2] ?? 5000);
+$colCount = 10;
+
+echo "=== Parallel Xlsx Writing Benchmark ===\n";
+echo "Sheets: {$sheetCount}, Rows/sheet: {$rowCount}, Cols/sheet: {$colCount}\n";
+echo 'CPU cores detected: ' . CpuDetector::detectCpuCount() . "\n";
+echo 'pcntl available: ' . (PcntlBackend::isAvailable() ? 'yes' : 'no') . "\n";
+echo 'Total cells: ' . ($sheetCount * $rowCount * $colCount) . "\n\n";
+
+// Build spreadsheet
+echo "Building spreadsheet...\n";
+$buildStart = microtime(true);
+$spreadsheet = new Spreadsheet();
+
+for ($s = 0; $s < $sheetCount; ++$s) {
+    $sheet = ($s === 0) ? $spreadsheet->getActiveSheet() : $spreadsheet->createSheet();
+    $sheet->setTitle("Sheet{$s}");
+
+    for ($row = 1; $row <= $rowCount; ++$row) {
+        for ($col = 1; $col <= $colCount; ++$col) {
+            $sheet->setCellValue([$col, $row], "S{$s}R{$row}C{$col}");
+        }
+    }
+}
+$buildTime = microtime(true) - $buildStart;
+$peakAfterBuild = memory_get_peak_usage(true);
+echo sprintf("Build time: %.3fs, Peak memory: %.1fMB\n\n", $buildTime, $peakAfterBuild / 1048576);
+
+// Sequential write
+echo "--- Sequential write ---\n";
+$tempSeq = tempnam(sys_get_temp_dir(), 'bench_seq_');
+$seqStart = microtime(true);
+$writer = new Xlsx($spreadsheet);
+$writer->save($tempSeq);
+$seqTime = microtime(true) - $seqStart;
+$seqSize = filesize($tempSeq);
+echo sprintf("Time: %.3fs, File size: %.1fKB\n", $seqTime, ($seqSize ?: 0) / 1024);
+@unlink($tempSeq);
+
+// Parallel write
+if (PcntlBackend::isAvailable()) {
+    echo "\n--- Parallel write ---\n";
+
+    $tempPar = tempnam(sys_get_temp_dir(), 'bench_par_');
+    $parStart = microtime(true);
+    $writer2 = new Xlsx($spreadsheet);
+    $writer2->setParallelEnabled(true);
+    // $writer2->setMaxWorkers(4); // Optional: override auto-detect
+    $writer2->save($tempPar);
+    $parTime = microtime(true) - $parStart;
+    $parSize = filesize($tempPar);
+    echo sprintf("Time: %.3fs, File size: %.1fKB\n", $parTime, ($parSize ?: 0) / 1024);
+    @unlink($tempPar);
+
+    echo "\n--- Results ---\n";
+    $speedup = $seqTime / $parTime;
+    $saved = (1 - ($parTime / $seqTime)) * 100;
+    echo sprintf("Sequential: %.3fs\n", $seqTime);
+    echo sprintf("Parallel:   %.3fs\n", $parTime);
+    echo sprintf("Speedup:    %.2fx (%.1f%% faster)\n", $speedup, $saved);
+} else {
+    echo "\npcntl not available — parallel benchmark skipped.\n";
+}
+
+echo sprintf("\nPeak memory: %.1fMB\n", memory_get_peak_usage(true) / 1048576);
+
+$spreadsheet->disconnectWorksheets();

samples/ParallelProfile.php

@@ -0,0 +1,80 @@
+<?php
+
+/**
+ * Profile where time is spent in Xlsx::save() to identify real bottlenecks.
+ */
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
+
+require __DIR__ . '/../vendor/autoload.php';
+
+$sheetCount = (int) ($argv[1] ?? 5);
+$rowCount = (int) ($argv[2] ?? 5000);
+$colCount = 10;
+
+echo "Building {$sheetCount} sheets x {$rowCount} rows x {$colCount} cols...\n";
+$spreadsheet = new Spreadsheet();
+for ($s = 0; $s < $sheetCount; ++$s) {
+    $sheet = ($s === 0) ? $spreadsheet->getActiveSheet() : $spreadsheet->createSheet();
+    $sheet->setTitle("Sheet{$s}");
+    for ($row = 1; $row <= $rowCount; ++$row) {
+        for ($col = 1; $col <= $colCount; ++$col) {
+            $sheet->setCellValue([$col, $row], "S{$s}R{$row}C{$col}");
+        }
+    }
+}
+echo "Done building.\n\n";
+
+// Time individual components by using reflection/hooks
+$writer = new Xlsx($spreadsheet);
+
+// Time createStringTable
+$t = microtime(true);
+$ref = new ReflectionMethod($writer, 'createStringTable');
+$ref->setAccessible(true);
+$ref->invoke($writer);
+$stringTableTime = microtime(true) - $t;
+
+// Time createStyleDictionaries
+$t = microtime(true);
+$ref2 = new ReflectionMethod($writer, 'createStyleDictionaries');
+$ref2->setAccessible(true);
+$ref2->invoke($writer);
+$styleTime = microtime(true) - $t;
+
+// Time per-sheet writeWorksheet
+$stringTableProp = new ReflectionProperty($writer, 'stringTable');
+$stringTableProp->setAccessible(true);
+$stringTable = $stringTableProp->getValue($writer);
+
+$worksheetWriter = $writer->getWriterPartWorksheet();
+$sheetTimes = [];
+for ($i = 0; $i < $sheetCount; ++$i) {
+    $t = microtime(true);
+    /** @var array<string> $stringTable */
+    $xml = $worksheetWriter->writeWorksheet($spreadsheet->getSheet($i), $stringTable, false);
+    $sheetTimes[$i] = microtime(true) - $t;
+}
+$totalSheetTime = array_sum($sheetTimes);
+
+// Time full save
+$tempFile = tempnam(sys_get_temp_dir(), 'profile_');
+$writer2 = new Xlsx($spreadsheet);
+$t = microtime(true);
+$writer2->save($tempFile);
+$totalSaveTime = microtime(true) - $t;
+@unlink($tempFile);
+
+echo "=== Time Breakdown ===\n";
+echo sprintf("createStringTable:      %.3fs  (%.1f%%)\n", $stringTableTime, $stringTableTime / $totalSaveTime * 100);
+echo sprintf("createStyleDictionaries: %.3fs  (%.1f%%)\n", $styleTime, $styleTime / $totalSaveTime * 100);
+echo sprintf("writeWorksheet (all):   %.3fs  (%.1f%%)\n", $totalSheetTime, $totalSheetTime / $totalSaveTime * 100);
+for ($i = 0; $i < $sheetCount; ++$i) {
+    echo sprintf("  sheet %d:              %.3fs\n", $i, $sheetTimes[$i]);
+}
+$otherTime = $totalSaveTime - $stringTableTime - $styleTime - $totalSheetTime;
+echo sprintf("other (zip, rels, etc): %.3fs  (%.1f%%)\n", $otherTime, $otherTime / $totalSaveTime * 100);
+echo sprintf("TOTAL save():           %.3fs\n", $totalSaveTime);
+
+$spreadsheet->disconnectWorksheets();

src/PhpSpreadsheet/Parallel/Backend/BackendInterface.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheet\Parallel\Backend;
+
+use Closure;
+
+interface BackendInterface
+{
+    /**
+     * Execute tasks in parallel (or sequentially for the fallback backend).
+     *
+     * @param list<mixed> $tasks Array of task inputs
+     * @param Closure $worker Function that receives a task input and returns a result
+     * @param int $maxWorkers Maximum number of concurrent workers
+     *
+     * @return list<mixed> Results in the same order as tasks
+     */
+    public function execute(array $tasks, Closure $worker, int $maxWorkers): array;
+
+    public static function isAvailable(): bool;
+}

src/PhpSpreadsheet/Parallel/Backend/ParallelTaskError.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheet\Parallel\Backend;
+
+/**
+ * Serializable error container passed from child to parent via IPC.
+ */
+class ParallelTaskError
+{
+    private string $message;
+
+    private int $code;
+
+    public function __construct(string $message, int $code = 0)
+    {
+        $this->message = $message;
+        $this->code = $code;
+    }
+
+    public function getMessage(): string
+    {
+        return $this->message;
+    }
+
+    public function getCode(): int
+    {
+        return $this->code;
+    }
+}