diff options
Diffstat (limited to 'app/models/internal_id.rb')
-rw-r--r-- | app/models/internal_id.rb | 36 |
1 files changed, 35 insertions, 1 deletions
diff --git a/app/models/internal_id.rb b/app/models/internal_id.rb index f50f28deffe..e5d0f94073c 100644 --- a/app/models/internal_id.rb +++ b/app/models/internal_id.rb @@ -1,6 +1,9 @@ # An InternalId is a strictly monotone sequence of integers # generated for a given scope and usage. # +# The monotone sequence may be broken if an ID is explicitly provided +# to `.track_greatest_and_save!` or `#track_greatest`. +# # For example, issues use their project to scope internal ids: # In that sense, scope is "project" and usage is "issues". # Generated internal ids for an issue are unique per project. @@ -25,13 +28,34 @@ class InternalId < ActiveRecord::Base # The operation locks the record and gathers a `ROW SHARE` lock (in PostgreSQL). # As such, the increment is atomic and safe to be called concurrently. def increment_and_save! + update_and_save { self.last_value = (last_value || 0) + 1 } + end + + # Increments #last_value with new_value if it is greater than the current, + # and saves the record + # + # The operation locks the record and gathers a `ROW SHARE` lock (in PostgreSQL). + # As such, the increment is atomic and safe to be called concurrently. + def track_greatest_and_save!(new_value) + update_and_save { self.last_value = [last_value || 0, new_value].max } + end + + private + + def update_and_save(&block) lock! - self.last_value = (last_value || 0) + 1 + yield save! last_value end class << self + def track_greatest(subject, scope, usage, new_value, init) + return new_value unless available? + + InternalIdGenerator.new(subject, scope, usage, init).track_greatest(new_value) + end + def generate_next(subject, scope, usage, init) # Shortcut if `internal_ids` table is not available (yet) # This can be the case in other (unrelated) migration specs @@ -94,6 +118,16 @@ class InternalId < ActiveRecord::Base end end + # Create a record in internal_ids if one does not yet exist + # and set its new_value if it is higher than the current last_value + # + # Note this will acquire a ROW SHARE lock on the InternalId record + def track_greatest(new_value) + subject.transaction do + (lookup || create_record).track_greatest_and_save!(new_value) + end + end + private # Retrieve InternalId record for (project, usage) combination, if it exists |