Added 2 mutexes to prevent weird race conditions when reading and writing from separate threads

This commit is contained in:
Samuel Hawksby-Robinson 2022-10-12 15:41:19 +01:00
parent a88ebe3a9f
commit 4cbe874dea
3 changed files with 35 additions and 21 deletions

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@ -1 +1 @@
0.112.0
0.112.1

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@ -5,31 +5,34 @@ import (
"sync"
)
// portManager is responsible for maintaining segregated access to the port field via the use of portWait sync.Mutex
// portManager is responsible for maintaining segregated access to the port field
// via the use of rwLock sync.RWMutex and mustRead sync.Mutex
// rwLock establishes a standard read write mutex that allows consecutive reads and exclusive writes
// mustRead forces MustGetPort to wait until port has a none 0 value
type portManger struct {
port int
afterPortChanged func(port int)
portWait *sync.Mutex
rwLock *sync.RWMutex
mustRead *sync.Mutex
}
// newPortManager returns a newly initialised portManager with a pre-Locked portManger.portWait sync.Mutex
// newPortManager returns a newly initialised portManager with a pre-Locked portManger.mustRead sync.Mutex
func newPortManager(afterPortChanged func(int)) portManger {
pm := portManger{
afterPortChanged: afterPortChanged,
portWait: new(sync.Mutex),
rwLock: new(sync.RWMutex),
mustRead: new(sync.Mutex),
}
pm.portWait.Lock()
pm.mustRead.Lock()
return pm
}
// SetPort sets the internal portManger.port field to the given port value
// SetPort sets portManger.port field to the given port value
// next triggers any given portManger.afterPortChanged function
// additionally portManger.portWait.Unlock() is called, releasing any calls to MustGetPort
// additionally portManger.mustRead.Unlock() is called, releasing any calls to MustGetPort
func (p *portManger) SetPort(port int) error {
// TryLock, multiple portManager.SetPort calls trigger `fatal error: sync: unlock of unlocked mutex`
// In the case of concurrent
// TODO fix this horrible thing
p.portWait.TryLock()
p.rwLock.Lock()
defer p.rwLock.Unlock()
if port == 0 {
return fmt.Errorf("port can not be `0`, use ResetPort() instead")
@ -39,29 +42,40 @@ func (p *portManger) SetPort(port int) error {
if p.afterPortChanged != nil {
p.afterPortChanged(port)
}
p.portWait.Unlock()
p.mustRead.Unlock()
return nil
}
// ResetPort attempts to reset portManger.port to 0
// if portManger.portWait is already locked the function returns after doing nothing
// if portManger.mustRead is already locked the function returns after doing nothing
// portManger.mustRead.TryLock() is called because ResetPort may be called multiple times in a row
// and calling multiple times must not cause a deadlock or an infinite hang, but the lock needs to be
// reapplied if it is not present.
func (p *portManger) ResetPort() {
if p.portWait.TryLock() {
p.rwLock.Lock()
defer p.rwLock.Unlock()
if p.mustRead.TryLock() {
p.port = 0
}
}
// GetPort gets the current value of portManager.port without any concern for the state of its value
// and therefore does not block until portManager.portWait.Unlock() is called
// and therefore does not block until portManager.mustRead.Unlock() is called
func (p *portManger) GetPort() int {
p.rwLock.RLock()
defer p.rwLock.RUnlock()
return p.port
}
// MustGetPort only returns portManager.port if portManager.portWait is unlocked.
// This presupposes that portManger.portWait has a default state of locked and SetPort unlock portManager.portWait
// MustGetPort only returns portManager.port if portManager.mustRead is unlocked.
// This presupposes that portManger.mustRead has a default state of locked and SetPort unlock portManager.mustRead
func (p *portManger) MustGetPort() int {
p.portWait.Lock()
defer p.portWait.Unlock()
p.mustRead.Lock()
defer p.mustRead.Unlock()
p.rwLock.RLock()
defer p.rwLock.RUnlock()
return p.port
}

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@ -40,7 +40,7 @@ func (s *ServerURLSuite) SetupTest() {
}}
go func() {
time.Sleep(waitTime)
s.serverNoPort.portWait.Unlock()
s.serverNoPort.mustRead.Unlock()
}()
s.testStart = time.Now()