Added stub / spec for executor interface

client/exec/exec.go

@@ -0,0 +1,47 @@
+// Package exec is used to invoke child processes across various operating
+// systems and child processes and provide the following features:
+//
+// - Least privilege
+// - Resource constraints
+// - Process isolation
+//
+// The semantics and implementation for these differ between operating systems,
+// operating system versions, and types of child processes. For example, running
+// Docker on Linux has different semantics than running Java on Windows. Also,
+// versions of an OS may provide different capabilities for resource isolation,
+// such as ulimits, cgroups, containers, jails, etc. Please refer to the
+// relevant implementation for specific details.
+package exec
+
+import "github.com/hashicorp/nomad/nomad/structs"
+
+type Command struct {
+	// This may be a username or Uid. The implementation will decide how to use it.
+	UserID string
+}
+
+type Executor interface {
+	// Limit must be called before Start and restricts the amount of resources
+	// the process can use
+	Limit(structs.Resources)
+
+	// Start the process. This may wrap the actual process in another command,
+	// depending on the capabilities in this environment.
+	Start() error
+
+	// Shutdown should use a graceful stop mechanism so the application can
+	// perform checkpointing or cleanup, if such a mechanism is available.
+	// If such a mechanism is not available, Showdown() should call ForceStop().
+	Shutdown() error
+
+	// ForceStop will terminate the process without waiting for cleanup. Every
+	// implementations must provide this.
+	ForceStop() error
+}
+
+// DefaultExecutor uses capability testing to give you the best available
+// executor based on your platform and execution environment. If you need a
+// specific executor, call it directly.
+func DefaultExecutor() Executor {
+	// TODO Implement this
+}

client/exec/exec_linux.go

@@ -0,0 +1,3 @@
+package exec
+
+// TODO Implement this!