Adds logic for tracking ipc storage driver process status

This allows requests to not hang if the child process exits

storagedriver/ipc/client.go

@@ -3,6 +3,7 @@ package ipc
 import (
 	"bytes"
 	"encoding/json"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"net"
@@ -15,23 +16,29 @@ import (
 	"github.com/docker/libchan/spdy"
 )
 
-// StorageDriverExecutablePrefix is the prefix which the IPC storage driver loader expects driver
+// StorageDriverExecutablePrefix is the prefix which the IPC storage driver
-// executables to begin with. For example, the s3 driver should be named "registry-storage-s3".
+// loader expects driver executables to begin with. For example, the s3 driver
+// should be named "registry-storagedriver-s3".
 const StorageDriverExecutablePrefix = "registry-storagedriver-"
 
-// StorageDriverClient is a storagedriver.StorageDriver implementation using a managed child process
+// StorageDriverClient is a storagedriver.StorageDriver implementation using a
-// communicating over IPC using libchan with a unix domain socket
+// managed child process communicating over IPC using libchan with a unix domain
+// socket
 type StorageDriverClient struct {
 	subprocess *exec.Cmd
+	exitChan   chan error
+	exitErr    error
+	stopChan   chan struct{}
 	socket     *os.File
 	transport  *spdy.Transport
 	sender     libchan.Sender
 	version    storagedriver.Version
 }
 
-// NewDriverClient constructs a new out-of-process storage driver using the driver name and
+// NewDriverClient constructs a new out-of-process storage driver using the
-// configuration parameters
+// driver name and configuration parameters
-// A user must call Start on this driver client before remote method calls can be made
+// A user must call Start on this driver client before remote method calls can
+// be made
 //
 // Looks for drivers in the following locations in order:
 // - Storage drivers directory (to be determined, yet not implemented)
@@ -56,9 +63,13 @@ func NewDriverClient(name string, parameters map[string]string) (*StorageDriverC
 	}, nil
 }
 
-// Start starts the designated child process storage driver and binds a socket to this process for
+// Start starts the designated child process storage driver and binds a socket
-// IPC method calls
+// to this process for IPC method calls
 func (driver *StorageDriverClient) Start() error {
+	driver.exitErr = nil
+	driver.exitChan = make(chan error)
+	driver.stopChan = make(chan struct{})
+
 	fileDescriptors, err := syscall.Socketpair(syscall.AF_LOCAL, syscall.SOCK_STREAM, 0)
 	if err != nil {
 		return err
@@ -76,6 +87,8 @@ func (driver *StorageDriverClient) Start() error {
 		return err
 	}
 
+	go driver.handleSubprocessExit()
+
 	if err = childSocket.Close(); err != nil {
 		driver.Stop()
 		return err
@@ -142,6 +155,10 @@ func (driver *StorageDriverClient) Stop() error {
 	if driver.subprocess != nil {
 		killErr = driver.subprocess.Process.Kill()
 	}
+	if driver.stopChan != nil {
+		driver.stopChan <- struct{}{}
+		close(driver.stopChan)
+	}
 
 	if closeSenderErr != nil {
 		return closeSenderErr
@@ -150,12 +167,17 @@ func (driver *StorageDriverClient) Stop() error {
 	} else if closeSocketErr != nil {
 		return closeSocketErr
 	}
+
 	return killErr
 }
 
 // Implement the storagedriver.StorageDriver interface over IPC
 
 func (driver *StorageDriverClient) GetContent(path string) ([]byte, error) {
+	if err := driver.exited(); err != nil {
+		return nil, err
+	}
+
 	receiver, remoteSender := libchan.Pipe()
 
 	params := map[string]interface{}{"Path": path}
@@ -164,8 +186,8 @@ func (driver *StorageDriverClient) GetContent(path string) ([]byte, error) {
 		return nil, err
 	}
 
-	var response ReadStreamResponse
+	response := new(ReadStreamResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return nil, err
 	}
@@ -183,6 +205,10 @@ func (driver *StorageDriverClient) GetContent(path string) ([]byte, error) {
 }
 
 func (driver *StorageDriverClient) PutContent(path string, contents []byte) error {
+	if err := driver.exited(); err != nil {
+		return err
+	}
+
 	receiver, remoteSender := libchan.Pipe()
 
 	params := map[string]interface{}{"Path": path, "Reader": ioutil.NopCloser(bytes.NewReader(contents))}
@@ -191,8 +217,8 @@ func (driver *StorageDriverClient) PutContent(path string, contents []byte) erro
 		return err
 	}
 
-	var response WriteStreamResponse
+	response := new(WriteStreamResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return err
 	}
@@ -205,16 +231,19 @@ func (driver *StorageDriverClient) PutContent(path string, contents []byte) erro
 }
 
 func (driver *StorageDriverClient) ReadStream(path string, offset uint64) (io.ReadCloser, error) {
-	receiver, remoteSender := libchan.Pipe()
+	if err := driver.exited(); err != nil {
+		return nil, err
+	}
 
+	receiver, remoteSender := libchan.Pipe()
 	params := map[string]interface{}{"Path": path, "Offset": offset}
 	err := driver.sender.Send(&Request{Type: "ReadStream", Parameters: params, ResponseChannel: remoteSender})
 	if err != nil {
 		return nil, err
 	}
 
-	var response ReadStreamResponse
+	response := new(ReadStreamResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return nil, err
 	}
@@ -227,16 +256,19 @@ func (driver *StorageDriverClient) ReadStream(path string, offset uint64) (io.Re
 }
 
 func (driver *StorageDriverClient) WriteStream(path string, offset, size uint64, reader io.ReadCloser) error {
-	receiver, remoteSender := libchan.Pipe()
+	if err := driver.exited(); err != nil {
+		return err
+	}
 
+	receiver, remoteSender := libchan.Pipe()
 	params := map[string]interface{}{"Path": path, "Offset": offset, "Size": size, "Reader": ioutil.NopCloser(reader)}
 	err := driver.sender.Send(&Request{Type: "WriteStream", Parameters: params, ResponseChannel: remoteSender})
 	if err != nil {
 		return err
 	}
 
-	var response WriteStreamResponse
+	response := new(WriteStreamResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return err
 	}
@@ -249,16 +281,19 @@ func (driver *StorageDriverClient) WriteStream(path string, offset, size uint64,
 }
 
 func (driver *StorageDriverClient) CurrentSize(path string) (uint64, error) {
-	receiver, remoteSender := libchan.Pipe()
+	if err := driver.exited(); err != nil {
+		return 0, err
+	}
 
+	receiver, remoteSender := libchan.Pipe()
 	params := map[string]interface{}{"Path": path}
 	err := driver.sender.Send(&Request{Type: "CurrentSize", Parameters: params, ResponseChannel: remoteSender})
 	if err != nil {
 		return 0, err
 	}
 
-	var response CurrentSizeResponse
+	response := new(CurrentSizeResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return 0, err
 	}
@@ -271,16 +306,19 @@ func (driver *StorageDriverClient) CurrentSize(path string) (uint64, error) {
 }
 
 func (driver *StorageDriverClient) List(path string) ([]string, error) {
-	receiver, remoteSender := libchan.Pipe()
+	if err := driver.exited(); err != nil {
+		return nil, err
+	}
 
+	receiver, remoteSender := libchan.Pipe()
 	params := map[string]interface{}{"Path": path}
 	err := driver.sender.Send(&Request{Type: "List", Parameters: params, ResponseChannel: remoteSender})
 	if err != nil {
 		return nil, err
 	}
 
-	var response ListResponse
+	response := new(ListResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return nil, err
 	}
@@ -293,16 +331,19 @@ func (driver *StorageDriverClient) List(path string) ([]string, error) {
 }
 
 func (driver *StorageDriverClient) Move(sourcePath string, destPath string) error {
-	receiver, remoteSender := libchan.Pipe()
+	if err := driver.exited(); err != nil {
+		return err
+	}
 
+	receiver, remoteSender := libchan.Pipe()
 	params := map[string]interface{}{"SourcePath": sourcePath, "DestPath": destPath}
 	err := driver.sender.Send(&Request{Type: "Move", Parameters: params, ResponseChannel: remoteSender})
 	if err != nil {
 		return err
 	}
 
-	var response MoveResponse
+	response := new(MoveResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return err
 	}
@@ -315,16 +356,19 @@ func (driver *StorageDriverClient) Move(sourcePath string, destPath string) erro
 }
 
 func (driver *StorageDriverClient) Delete(path string) error {
-	receiver, remoteSender := libchan.Pipe()
+	if err := driver.exited(); err != nil {
+		return err
+	}
 
+	receiver, remoteSender := libchan.Pipe()
 	params := map[string]interface{}{"Path": path}
 	err := driver.sender.Send(&Request{Type: "Delete", Parameters: params, ResponseChannel: remoteSender})
 	if err != nil {
 		return err
 	}
 
-	var response DeleteResponse
+	response := new(DeleteResponse)
-	err = receiver.Receive(&response)
+	err = driver.receiveResponse(receiver, response)
 	if err != nil {
 		return err
 	}
@@ -335,3 +379,66 @@ func (driver *StorageDriverClient) Delete(path string) error {
 
 	return nil
 }
+
+// handleSubprocessExit populates the exit channel until we have explicitly
+// stopped the storage driver subprocess
+// Requests can select on driver.exitChan and response receiving and not hang if
+// the process exits
+func (driver *StorageDriverClient) handleSubprocessExit() {
+	exitErr := driver.subprocess.Wait()
+	if exitErr == nil {
+		exitErr = fmt.Errorf("Storage driver subprocess already exited cleanly")
+	} else {
+		exitErr = fmt.Errorf("Storage driver subprocess exited with error: %s", exitErr)
+	}
+
+	driver.exitErr = exitErr
+
+	for {
+		select {
+		case driver.exitChan <- exitErr:
+		case <-driver.stopChan:
+			close(driver.exitChan)
+			return
+		}
+	}
+}
+
+// receiveResponse populates the response value with the next result from the
+// given receiver, or returns an error if receiving failed or the driver has
+// stopped
+func (driver *StorageDriverClient) receiveResponse(receiver libchan.Receiver, response interface{}) error {
+	receiveChan := make(chan error, 1)
+	go func(receiveChan chan<- error) {
+		defer close(receiveChan)
+		receiveChan <- receiver.Receive(response)
+	}(receiveChan)
+
+	var err error
+	var ok bool
+	select {
+	case err = <-receiveChan:
+	case err, ok = <-driver.exitChan:
+		go func(receiveChan <-chan error) {
+			<-receiveChan
+		}(receiveChan)
+		if !ok {
+			err = driver.exitErr
+		}
+	}
+
+	return err
+}
+
+// exited returns an exit error if the driver has exited or nil otherwise
+func (driver *StorageDriverClient) exited() error {
+	select {
+	case err, ok := <-driver.exitChan:
+		if !ok {
+			return driver.exitErr
+		}
+		return err
+	default:
+		return nil
+	}
+}