Transaction Locks that allow recursive RLocking

txnlock.c

#include <pthread.h>
#include <sys/types.h>

u_int64_t goid(void) {
  return (u_int64_t)pthread_self();
}

txnlock.go

package splitstore

import (
	"C"
	"runtime"
	"sync"
)

// A TxnLock is like a RWMutex but it allows recursive RLocking.
// This is necessary to support Views that can recursively operate on the blockstore without deadlock.
type TxnLock struct {
	rwlk  sync.RWMutex
	mx    sync.Mutex
	views map[uint64]int
}

// I will go to hell
func goid() uint64

func (l *TxnLock) Init() {
	l.views = make(map[uint64]int)
}

func (l *TxnLock) RLock() {
	runtime.LockOSThread()
	self := goid()

	l.mx.Lock()
	count := l.views[self]
	count++
	l.views[self] = count
	l.mx.Unlock()

	if count > 1 {
		return
	}

	l.rwlk.RLock()
}

func (l *TxnLock) RUnlock() {
	defer runtime.UnlockOSThread()
	self := goid()

	l.mx.Lock()
	count := l.views[self]
	count--
	l.views[self] = count
	l.mx.Unlock()

	if count > 0 {
		return
	}

	l.rwlk.RUnlock()
}

func (l *TxnLock) Lock() {
	l.rwlk.Lock()
}

func (l *TxnLock) Unlock() {
	l.rwlk.Unlock()
}