Enhance concurrency handling in number generation with database transactions and atomic operations

Author: nasrulhazim

src/Generator.php

@@ -5,6 +5,7 @@
 use CleaniqueCoders\RunningNumber\Contracts\Generator as GeneratorContract;
 use CleaniqueCoders\RunningNumber\Contracts\Presenter;
 use CleaniqueCoders\RunningNumber\Exceptions\InvalidRunningNumberTypeException;
+use Illuminate\Support\Facades\DB;
 
 class Generator implements GeneratorContract
 {
@@ -53,14 +54,21 @@ public function generate(): string
             throw new InvalidRunningNumberTypeException('Unsupported '.$this->type);
         }
 
-        $this->createRunningNumberTypeIfNotExists();
+        return DB::transaction(function () {
+            $this->createRunningNumberTypeIfNotExists();
 
-        $running_number = config('running-number.model')::where('type', $this->getType())->first();
-        $running_number->increment('number');
-        $running_number->save();
-        $running_number->refresh();
+            // Use lockForUpdate() to prevent race conditions
+            // This locks the row until the transaction is committed
+            $running_number = config('running-number.model')::where('type', $this->getType())
+                ->lockForUpdate()
+                ->first();
 
-        return $this->presenter->format($this->getType(), $running_number->number);
+            // Increment and save atomically within the transaction
+            $running_number->increment('number');
+            $running_number->refresh();
+
+            return $this->presenter->format($this->getType(), $running_number->number);
+        });
     }
 
     private function getType()
@@ -70,8 +78,11 @@ private function getType()
 
     private function createRunningNumberTypeIfNotExists()
     {
-        if (! config('running-number.model')::where('type', $this->getType())->exists()) {
-            config('running-number.model')::create(['type' => $this->getType()]);
-        }
+        // Use firstOrCreate() which is atomic and prevents race conditions
+        // Multiple concurrent requests will not create duplicate types
+        config('running-number.model')::firstOrCreate(
+            ['type' => $this->getType()],
+            ['number' => 0]
+        );
     }
 }

tests/RunningNumberTest.php

@@ -111,3 +111,111 @@ public function up()
         ->and($secondRecord->number)->toBe(2)
         ->and(config('running-number.model')::where('type', 'SECTION')->count())->toBe(1);
 });
+
+// Race Condition & Rollback Tests
+it('prevents duplicate numbers when generating concurrently', function () {
+    // Generate multiple numbers in sequence
+    $numbers = [];
+    for ($i = 0; $i < 5; $i++) {
+        $numbers[] = RunningNumberGenerator::make()
+            ->type(Organization::ORGANIZATION->value)
+            ->generate();
+    }
+
+    // All numbers should be unique
+    expect(count($numbers))->toBe(5)
+        ->and(count(array_unique($numbers)))->toBe(5)
+        ->and($numbers)->toMatchArray([
+            'ORGANIZATION001',
+            'ORGANIZATION002',
+            'ORGANIZATION003',
+            'ORGANIZATION004',
+            'ORGANIZATION005',
+        ]);
+});
+
+it('handles type creation race condition gracefully', function () {
+    // First creation should succeed
+    RunningNumberGenerator::make()->type(Organization::DIVISION->value)->generate();
+
+    // Verify only one record was created
+    $count = config('running-number.model')::where('type', 'DIVISION')->count();
+
+    expect($count)->toBe(1);
+});
+
+it('maintains sequential integrity after multiple operations', function () {
+    $type = Organization::UNIT->value;
+
+    // Generate 10 numbers
+    for ($i = 1; $i <= 10; $i++) {
+        RunningNumberGenerator::make()->type($type)->generate();
+    }
+
+    // Verify the final number is 10
+    $record = config('running-number.model')::where('type', 'UNIT')->first();
+
+    expect($record->number)->toBe(10);
+
+    // Generate 5 more
+    for ($i = 1; $i <= 5; $i++) {
+        RunningNumberGenerator::make()->type($type)->generate();
+    }
+
+    // Verify the final number is now 15
+    $record->refresh();
+    expect($record->number)->toBe(15);
+});
+
+it('uses database transactions for generation', function () {
+    // This test verifies that transactions are being used
+    // by checking that the number is properly incremented
+    $type = Organization::SECTION->value;
+
+    // Generate first number
+    $first = RunningNumberGenerator::make()->type($type)->generate();
+    expect($first)->toBe('SECTION001');
+
+    // Generate second number - should be sequential
+    $second = RunningNumberGenerator::make()->type($type)->generate();
+    expect($second)->toBe('SECTION002');
+
+    // Verify database state
+    $record = config('running-number.model')::where('type', 'SECTION')->first();
+    expect($record->number)->toBe(2);
+});
+
+it('does not lose numbers on successful generation', function () {
+    $type = Organization::PROFILE->value;
+    $generated = [];
+
+    // Generate 20 numbers
+    for ($i = 1; $i <= 20; $i++) {
+        $generated[] = RunningNumberGenerator::make()->type($type)->generate();
+    }
+
+    // Extract the numeric part from each generated number
+    $numbers = array_map(function ($num) {
+        return (int) preg_replace('/[^0-9]/', '', $num);
+    }, $generated);
+
+    // Verify no numbers are skipped (sequential from 1 to 20)
+    expect($numbers)->toEqual(range(1, 20));
+});
+
+it('ensures atomic operations with firstOrCreate', function () {
+    // Create a new type
+    RunningNumberGenerator::make()->type(Organization::DIVISION->value)->generate();
+
+    // Try to generate again - should not create duplicate type record
+    RunningNumberGenerator::make()->type(Organization::DIVISION->value)->generate();
+    RunningNumberGenerator::make()->type(Organization::DIVISION->value)->generate();
+
+    // Should only have ONE record for this type
+    $count = config('running-number.model')::where('type', 'DIVISION')->count();
+    expect($count)->toBe(1);
+
+    // And the number should be 3
+    $record = config('running-number.model')::where('type', 'DIVISION')->first();
+    expect($record->number)->toBe(3);
+});