init

at-admin/vendor/github.com/jtolds/gls/context.go

@@ -0,0 +1,153 @@
+// Package gls implements goroutine-local storage.
+package gls
+
+import (
+	"sync"
+)
+
+var (
+	mgrRegistry    = make(map[*ContextManager]bool)
+	mgrRegistryMtx sync.RWMutex
+)
+
+// Values is simply a map of key types to value types. Used by SetValues to
+// set multiple values at once.
+type Values map[interface{}]interface{}
+
+// ContextManager is the main entrypoint for interacting with
+// Goroutine-local-storage. You can have multiple independent ContextManagers
+// at any given time. ContextManagers are usually declared globally for a given
+// class of context variables. You should use NewContextManager for
+// construction.
+type ContextManager struct {
+	mtx    sync.Mutex
+	values map[uint]Values
+}
+
+// NewContextManager returns a brand new ContextManager. It also registers the
+// new ContextManager in the ContextManager registry which is used by the Go
+// method. ContextManagers are typically defined globally at package scope.
+func NewContextManager() *ContextManager {
+	mgr := &ContextManager{values: make(map[uint]Values)}
+	mgrRegistryMtx.Lock()
+	defer mgrRegistryMtx.Unlock()
+	mgrRegistry[mgr] = true
+	return mgr
+}
+
+// Unregister removes a ContextManager from the global registry, used by the
+// Go method. Only intended for use when you're completely done with a
+// ContextManager. Use of Unregister at all is rare.
+func (m *ContextManager) Unregister() {
+	mgrRegistryMtx.Lock()
+	defer mgrRegistryMtx.Unlock()
+	delete(mgrRegistry, m)
+}
+
+// SetValues takes a collection of values and a function to call for those
+// values to be set in. Anything further down the stack will have the set
+// values available through GetValue. SetValues will add new values or replace
+// existing values of the same key and will not mutate or change values for
+// previous stack frames.
+// SetValues is slow (makes a copy of all current and new values for the new
+// gls-context) in order to reduce the amount of lookups GetValue requires.
+func (m *ContextManager) SetValues(new_values Values, context_call func()) {
+	if len(new_values) == 0 {
+		context_call()
+		return
+	}
+
+	mutated_keys := make([]interface{}, 0, len(new_values))
+	mutated_vals := make(Values, len(new_values))
+
+	EnsureGoroutineId(func(gid uint) {
+		m.mtx.Lock()
+		state, found := m.values[gid]
+		if !found {
+			state = make(Values, len(new_values))
+			m.values[gid] = state
+		}
+		m.mtx.Unlock()
+
+		for key, new_val := range new_values {
+			mutated_keys = append(mutated_keys, key)
+			if old_val, ok := state[key]; ok {
+				mutated_vals[key] = old_val
+			}
+			state[key] = new_val
+		}
+
+		defer func() {
+			if !found {
+				m.mtx.Lock()
+				delete(m.values, gid)
+				m.mtx.Unlock()
+				return
+			}
+
+			for _, key := range mutated_keys {
+				if val, ok := mutated_vals[key]; ok {
+					state[key] = val
+				} else {
+					delete(state, key)
+				}
+			}
+		}()
+
+		context_call()
+	})
+}
+
+// GetValue will return a previously set value, provided that the value was set
+// by SetValues somewhere higher up the stack. If the value is not found, ok
+// will be false.
+func (m *ContextManager) GetValue(key interface{}) (
+	value interface{}, ok bool) {
+	gid, ok := GetGoroutineId()
+	if !ok {
+		return nil, false
+	}
+
+	m.mtx.Lock()
+	state, found := m.values[gid]
+	m.mtx.Unlock()
+
+	if !found {
+		return nil, false
+	}
+	value, ok = state[key]
+	return value, ok
+}
+
+func (m *ContextManager) getValues() Values {
+	gid, ok := GetGoroutineId()
+	if !ok {
+		return nil
+	}
+	m.mtx.Lock()
+	state, _ := m.values[gid]
+	m.mtx.Unlock()
+	return state
+}
+
+// Go preserves ContextManager values and Goroutine-local-storage across new
+// goroutine invocations. The Go method makes a copy of all existing values on
+// all registered context managers and makes sure they are still set after
+// kicking off the provided function in a new goroutine. If you don't use this
+// Go method instead of the standard 'go' keyword, you will lose values in
+// ContextManagers, as goroutines have brand new stacks.
+func Go(cb func()) {
+	mgrRegistryMtx.RLock()
+	defer mgrRegistryMtx.RUnlock()
+
+	for mgr := range mgrRegistry {
+		values := mgr.getValues()
+		if len(values) > 0 {
+			cb = func(mgr *ContextManager, cb func()) func() {
+				return func() { mgr.SetValues(values, cb) }
+			}(mgr, cb)
+		}
+	}
+
+	go cb()
+}