Parallel migrations (#57)

* parallelize migration-related commands

* Fix code style (php-cs-fixer)

---------

Co-authored-by: PHP CS Fixer <phpcsfixer@example.com>

src/Concerns/ParallelCommand.php

@@ -0,0 +1,105 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Stancl\Tenancy\Concerns;
+
+use ArrayAccess;
+use Illuminate\Support\Collection;
+use Illuminate\Support\Facades\DB;
+use Symfony\Component\Console\Input\InputOption;
+
+trait ParallelCommand
+{
+    public const int MAX_PROCESSES = 24;
+
+    abstract protected function childHandle(...$args): bool;
+
+    public function addProcessesOption(): void
+    {
+        $this->addOption('processes', 'p', InputOption::VALUE_OPTIONAL, 'How many processes to spawn. Maximum value: ' . static::MAX_PROCESSES . ', recommended value: core count', 1);
+    }
+
+    protected function forkProcess(...$args): int
+    {
+        $pid = pcntl_fork();
+
+        if ($pid === -1) {
+            return -1;
+        } else if ($pid) {
+            // Parent
+            return $pid;
+        } else {
+            // Child
+            DB::reconnect();
+
+            exit($this->childHandle(...$args) ? 0 : 1);
+        }
+    }
+
+    protected function getProcesses(): int
+    {
+        $processes = (int) $this->input->getOption('processes');
+
+        if (($processes < 0) || ($processes > static::MAX_PROCESSES)) {
+            $this->components->error("Maximum value for processes is " . static::MAX_PROCESSES);
+            exit(1);
+        }
+
+        if ($processes > 1 && ! function_exists('pcntl_fork')) {
+            $this->components->error("The pcntl extension is required for parallel migrations to work.");
+        }
+
+        return $processes;
+    }
+
+    protected function getTenantChunks(): Collection
+    {
+        $idCol = tenancy()->model()->getTenantKeyName();
+        $tenants = tenancy()->model()->orderBy($idCol, 'asc')->pluck($idCol);
+        return $tenants->chunk(ceil($tenants->count() / $this->getProcesses()));
+    }
+
+    protected function runConcurrently(array|ArrayAccess $args = null): int
+    {
+        $processes = $this->getProcesses();
+        $success = true;
+        $pids = [];
+
+        for ($i = 0; $i < $processes; $i++) {
+            $pid = $this->forkProcess($args !== null ? $args[$i] : null);
+
+            if ($pid === -1) {
+                $this->components->error("Unable to fork process (iteration $i)!");
+                if ($i === 0) {
+                    exit(1);
+                }
+            }
+
+            $pids[] = $pid;
+        }
+
+        // Fork equivalent of joining an array of join handles
+        foreach ($pids as $i => $pid) {
+            pcntl_waitpid($pid, $status);
+
+            $normalExit = pcntl_wifexited($status);
+
+            if ($normalExit) {
+                $exitCode = pcntl_wexitstatus($status);
+
+                if ($exitCode === 0) {
+                    $this->components->info("Child process [$i] (PID $pid) finished successfully.");
+                } else {
+                    $success = false;
+                    $this->components->error("Child process [$i] (PID $pid) completed with failures.");
+                }
+            } else {
+                $success = false;
+                $this->components->error("Child process [$i] (PID $pid) exited abnormally.");
+            }
+        }
+
+        return $success ? 0 : 1;
+    }
+}