From c237633d34d56d95b7f5e8e00488ed5d8e54b60b Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Sat, 15 Sep 2018 18:51:51 +0200
Subject: [PATCH] all: use a custom sync package

The sync package is strongly tied to the runtime, so it's easier to
implement a new one. Besides, it's pretty big so it's better to replace
it.
---
 src/runtime/sync.go | 12 -----------
 src/sync/mutex.go   | 52 +++++++++++++++++++++++++++++++++++++++++++++
 src/sync/once.go    | 16 ++++++++++++++
 3 files changed, 68 insertions(+), 12 deletions(-)
 create mode 100644 src/sync/mutex.go
 create mode 100644 src/sync/once.go

diff --git a/src/runtime/sync.go b/src/runtime/sync.go
index 765ecba2..7ccdf5f6 100644
--- a/src/runtime/sync.go
+++ b/src/runtime/sync.go
@@ -1,13 +1 @@
 package runtime
-
-// This file contains support code for the sync package.
-
-//go:linkname registerPoolCleanup sync.runtime_registerPoolCleanup
-func registerPoolCleanup(cleanup func()) {
-	// Ignore.
-}
-
-//go:linkname notifyListCheck sync.runtime_notifyListCheck
-func notifyListCheck(size uintptr) {
-	// Ignore.
-}
diff --git a/src/sync/mutex.go b/src/sync/mutex.go
new file mode 100644
index 00000000..4e89285f
--- /dev/null
+++ b/src/sync/mutex.go
@@ -0,0 +1,52 @@
+package sync
+
+// These mutexes assume there is only one thread of operation: no goroutines,
+// interrupts or anything else.
+
+type Mutex struct {
+	locked bool
+}
+
+func (m *Mutex) Lock() {
+	if m.locked {
+		panic("todo: block on locked mutex")
+	}
+	m.locked = true
+}
+
+func (m *Mutex) Unlock() {
+	if !m.locked {
+		panic("sync: unlock of unlocked Mutex")
+	}
+	m.locked = false
+}
+
+type RWMutex struct {
+	m       Mutex
+	readers uint32
+}
+
+func (rw *RWMutex) Lock() {
+	rw.m.Lock()
+}
+
+func (rw *RWMutex) Unlock() {
+	rw.m.Unlock()
+}
+
+func (rw *RWMutex) RLock() {
+	if rw.readers == 0 {
+		rw.m.Lock()
+	}
+	rw.readers++
+}
+
+func (rw *RWMutex) RUnlock() {
+	if rw.readers == 0 {
+		panic("sync: unlock of unlocked RWMutex")
+	}
+	rw.readers--
+	if rw.readers == 0 {
+		rw.m.Unlock()
+	}
+}
diff --git a/src/sync/once.go b/src/sync/once.go
new file mode 100644
index 00000000..118237c9
--- /dev/null
+++ b/src/sync/once.go
@@ -0,0 +1,16 @@
+package sync
+
+type Once struct {
+	done bool
+	m    Mutex
+}
+
+func (o *Once) Do(f func()) {
+	o.m.Lock()
+	defer o.m.Unlock()
+	if o.done {
+		return
+	}
+	o.done = true
+	f()
+}