Add build scheduler DB interface, dumb in-memory impl, cache

build_scheduler/go/db/db.go

+package db
+
+import (
+        "errors"
+        "time"
+
+        "go.skia.org/infra/go/buildbucket"
+)
+
+const (
+        // Maximum number of simultaneous GetModifiedBuilds users.
+        MAX_MODIFIED_BUILDS_USERS = 10
+
+        // Expiration for GetModifiedBuilds users.
+        MODIFIED_BUILDS_TIMEOUT = 10 * time.Minute
+)
+
+var (
+        ErrTooManyUsers = errors.New("Too many users")
+        ErrUnknownId    = errors.New("Unknown ID")
+)
+
+func IsTooManyUsers(e error) bool {
+        return e != nil && e.Error() == ErrTooManyUsers.Error()
+}
+
+func IsUnknownId(e error) bool {
+        return e != nil && e.Error() == ErrUnknownId.Error()
+}
+
+type Build struct {
+        *buildbucket.Build
+        Commits []string
+}
+
+func (b *Build) Copy() *Build {
+        commits := make([]string, len(b.Commits))
+        copy(commits, b.Commits)
+        rv := &Build{
+                Build:   b.Build.Copy(),
+                Commits: commits,
+        }
+        return rv
+}
+
+type DB interface {
+        // Close the [connection to the] DB.
+        Close() error
+
+        // GetBuildsFromDateRange retrieves all builds which started in the given date range.
+        GetBuildsFromDateRange(time.Time, time.Time) ([]*Build, error)
+
+        // GetModifiedBuilds returns all builds modified since the last time
+        // GetModifiedBuilds was run with the given id.
+        GetModifiedBuilds(string) ([]*Build, error)
+
+        // PutBuild inserts or updates the Build in the database.
+        PutBuild(*Build) error
+
+        // PutBuilds inserts or updates the Builds in the database.
+        PutBuilds([]*Build) error
+
+        // StartTrackingModifiedBuilds initiates tracking of modified builds for
+        // the current caller. Returns a unique ID which can be used by the caller
+        // to retrieve builds which have been modified since the last query. The ID
+        // expires after a period of inactivity.
+        StartTrackingModifiedBuilds() (string, error)
+}