Improve description of Running and Paused booleans

Commit abd72d4 added a "FIXME" comment to the container "State", mentioning that a container cannot be both "Running" and "Paused". This comment was incorrect, because containers on Linux actually _must_ be running in order to be paused. This patch adds additional information both in a comment, and in the API documentation to clarify that these booleans are not mutually exclusive. Signed-off-by: Sebastiaan van Stijn <[email protected]>
ramkrivas · May 19, 2017 · b654b62 · b654b62
1 parent ab83b92
commit b654b62
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Showing 3 changed files with 19 additions and 5 deletions.
diff --git a/api/swagger.yaml b/api/swagger.yaml
@@ -3107,10 +3107,22 @@ paths:
                 type: "object"
                 properties:
                   Status:
-                    description: "The status of the container. For example, `running` or `exited`."
+                    description: |
+                      The status of the container. For example, `"running"` or `"exited"`.
                     type: "string"
+                    enum: ["created", "running", "paused", "restarting", "removing", "exited", "dead"]
                   Running:
-                    description: "Whether this container is running."
+                    description: |
+                      Whether this container is running.
+
+                      Note that a running container can be _paused_. The `Running` and `Paused`
+                      booleans are not mutually exclusive:
+
+                      When pausing a container (on Linux), the cgroups freezer is used to suspend
+                      all processes in the container. Freezing the process requires the process to
+                      be running. As a result, paused containers are both `Running` _and_ `Paused`.
+
+                      Use the `Status` field instead to determin if a container's state is "running".
                     type: "boolean"
                   Paused:
                     description: "Whether this container is paused."

diff --git a/api/types/types.go b/api/types/types.go
@@ -277,7 +277,7 @@ type Health struct {
 // ContainerState stores container's running state
 // it's part of ContainerJSONBase and will return by "inspect" command
 type ContainerState struct {
-	Status     string
+	Status     string // String representation of the container state. Can be one of "created", "running", "paused", "restarting", "removing", "exited", or "dead"
 	Running    bool
 	Paused     bool
 	Restarting bool

diff --git a/container/state.go b/container/state.go
@@ -17,8 +17,10 @@ import (
 // functions defined against State to run against Container.
 type State struct {
 	sync.Mutex
-	// FIXME: Why do we have both paused and running if a
-	// container cannot be paused and running at the same time?
+	// Note that `Running` and `Paused` are not mutually exclusive:
+	// When pausing a container (on Linux), the cgroups freezer is used to suspend
+	// all processes in the container. Freezing the process requires the process to
+	// be running. As a result, paused containers are both `Running` _and_ `Paused`.
 	Running           bool
 	Paused            bool
 	Restarting        bool