Add interface for libpod multiprocess locks

Signed-off-by: Matthew Heon <matthew.heon@gmail.com>

1 files changed, 244 insertions, 0 deletions

diff --git a/libpod/lock/shm_lock_test.go b/libpod/lock/shm_lock_test.go
new file mode 100644
index 000000000..6d4525f6a
--- /dev/null
+++ b/libpod/lock/shm_lock_test.go
@@ -0,0 +1,244 @@
+package lock
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+	"time"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// All tests here are in the same process, which somewhat limits their utility
+// The big intent of this package it multiprocess locking, which is really hard
+// to test without actually having multiple processes...
+// We can at least verify that the locks work within the local process.
+
+// 4 * BITMAP_SIZE to ensure we have to traverse bitmaps
+const numLocks = 128
+
+// We need a test main to ensure that the SHM is created before the tests run
+func TestMain(m *testing.M) {
+	shmLock, err := CreateSHMLock(numLocks)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Error creating SHM for tests: %v\n", err)
+		os.Exit(-1)
+	}
+
+	// Close the SHM - every subsequent test will reopen
+	if err := shmLock.Close(); err != nil {
+		fmt.Fprintf(os.Stderr, "Error closing SHM locks: %v\n", err)
+		os.Exit(-1)
+	}
+
+	exitCode := m.Run()
+
+	// We need to remove the SHM segment to clean up after ourselves
+	os.RemoveAll("/dev/shm/libpod_lock")
+
+	os.Exit(exitCode)
+}
+
+
+func runLockTest(t *testing.T, testFunc func(*testing.T, *SHMLocks)) {
+	locks, err := OpenSHMLock(numLocks)
+	if err != nil {
+		t.Fatalf("Error opening locks: %v", err)
+	}
+	defer func() {
+		// Unlock and deallocate all locks
+		// Ignore EBUSY (lock is already unlocked)
+		// Ignore ENOENT (lock is not allocated)
+		var i uint32
+		for i = 0; i < numLocks; i++ {
+			if err := locks.UnlockSemaphore(i); err != nil && err != syscall.EBUSY {
+				t.Fatalf("Error unlocking semaphore %d: %v", i, err)
+			}
+			if err := locks.DeallocateSemaphore(i); err != nil && err != syscall.ENOENT {
+				t.Fatalf("Error deallocating semaphore %d: %v", i, err)
+			}
+		}
+
+		if err := locks.Close(); err != nil {
+			t.Fatalf("Error closing locks: %v", err)
+		}
+	}()
+
+	success := t.Run("locks", func (t *testing.T) {
+		testFunc(t, locks)
+	})
+	if !success {
+		t.Fail()
+	}
+}
+
+// Test that creating an SHM with a bad size fails
+func TestCreateNewSHMBadSize(t *testing.T) {
+	// Odd number, not a power of 2, should never be a word size on a system
+	_, err := CreateSHMLock(7)
+	assert.Error(t, err)
+}
+
+// Test that creating an SHM with 0 size fails
+func TestCreateNewSHMZeroSize(t *testing.T) {
+	_, err := CreateSHMLock(0)
+	assert.Error(t, err)
+}
+
+// Test that deallocating an unallocated lock errors
+func TestDeallocateUnallocatedLockErrors(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		err := locks.DeallocateSemaphore(0)
+		assert.Error(t, err)
+	})
+}
+
+// Test that unlocking an unlocked lock fails
+func TestUnlockingUnlockedLockFails(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		err := locks.UnlockSemaphore(0)
+		assert.Error(t, err)
+	})
+}
+
+// Test that locking and double-unlocking fails
+func TestDoubleUnlockFails(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		err := locks.LockSemaphore(0)
+		assert.NoError(t, err)
+
+		err = locks.UnlockSemaphore(0)
+		assert.NoError(t, err)
+
+		err = locks.UnlockSemaphore(0)
+		assert.Error(t, err)
+	})
+}
+
+// Test allocating - lock - unlock - deallocate cycle, single lock
+func TestLockLifecycleSingleLock(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		sem, err := locks.AllocateSemaphore()
+		require.NoError(t, err)
+
+		err = locks.LockSemaphore(sem)
+		assert.NoError(t, err)
+
+		err = locks.UnlockSemaphore(sem)
+		assert.NoError(t, err)
+
+		err = locks.DeallocateSemaphore(sem)
+		assert.NoError(t, err)
+	})
+}
+
+// Test allocate two locks returns different locks
+func TestAllocateTwoLocksGetsDifferentLocks(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		sem1, err := locks.AllocateSemaphore()
+		assert.NoError(t, err)
+
+		sem2, err := locks.AllocateSemaphore()
+		assert.NoError(t, err)
+
+		assert.NotEqual(t, sem1, sem2)
+	})
+}
+
+// Test allocate all locks successful and all are unique
+func TestAllocateAllLocksSucceeds(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		sems := make(map[uint32]bool)
+		for i := 0; i < numLocks; i++ {
+			sem, err := locks.AllocateSemaphore()
+			assert.NoError(t, err)
+
+			// Ensure the allocate semaphore is unique
+			_, ok := sems[sem]
+			assert.False(t, ok)
+
+			sems[sem] = true
+		}
+	})
+}
+
+// Test allocating more than the given max fails
+func TestAllocateTooManyLocksFails(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		// Allocate all locks
+		for i := 0; i < numLocks; i++ {
+			_, err := locks.AllocateSemaphore()
+			assert.NoError(t, err)
+		}
+
+		// Try and allocate one more
+		_, err := locks.AllocateSemaphore()
+		assert.Error(t, err)
+	})
+}
+
+// Test allocating max locks, deallocating one, and then allocating again succeeds
+func TestAllocateDeallocateCycle(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		// Allocate all locks
+		for i := 0; i < numLocks; i++ {
+			_, err := locks.AllocateSemaphore()
+			assert.NoError(t, err)
+		}
+
+		// Now loop through again, deallocating and reallocating.
+		// Each time we free 1 semaphore, allocate again, and make sure
+		// we get the same semaphore back.
+		var j uint32
+		for j = 0; j < numLocks; j++ {
+			err := locks.DeallocateSemaphore(j)
+			assert.NoError(t, err)
+
+			newSem, err := locks.AllocateSemaphore()
+			assert.NoError(t, err)
+			assert.Equal(t, j, newSem)
+		}
+	})
+}
+
+// Test that locks actually lock
+func TestLockSemaphoreActuallyLocks(t *testing.T) {
+	runLockTest(t, func(t *testing.T, locks *SHMLocks) {
+		// This entire test is very ugly - lots of sleeps to try and get
+		// things to occur in the right order.
+		// It also doesn't even exercise the multiprocess nature of the
+		// locks.
+
+		// Get the current time
+		startTime := time.Now()
+
+		// Start a goroutine to take the lock and then release it after
+		// a second.
+		go func() {
+			err := locks.LockSemaphore(0)
+			assert.NoError(t, err)
+
+			time.Sleep(1 * time.Second)
+
+			err = locks.UnlockSemaphore(0)
+			assert.NoError(t, err)
+		}()
+
+		// Sleep for a quarter of a second to give the goroutine time
+		// to kick off and grab the lock
+		time.Sleep(250 * time.Millisecond)
+
+		// Take the lock
+		err := locks.LockSemaphore(0)
+		assert.NoError(t, err)
+
+		// Get the current time
+		endTime := time.Now()
+
+		// Verify that at least 1 second has passed since start
+		duration := endTime.Sub(startTime)
+		assert.True(t, duration.Seconds() > 1.0)
+	})
+}