From bef46e795448470041493d4f80e86d1342ba3923 Mon Sep 17 00:00:00 2001
From: Nuno Cruces <ncruces@users.noreply.github.com>
Date: Thu, 23 Mar 2023 12:40:55 +0000
Subject: [PATCH] Locking improvements (windows).

---
 vfs_lock.go       | 14 --------------
 vfs_os_unix.go    |  9 +++++++++
 vfs_os_windows.go | 16 +++++++++++++++-
 3 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/vfs_lock.go b/vfs_lock.go
index 2213224..a67cb92 100644
--- a/vfs_lock.go
+++ b/vfs_lock.go
@@ -89,10 +89,6 @@ func vfsLock(ctx context.Context, mod api.Module, pFile uint32, eLock vfsLockSta
 		if cLock != _NO_LOCK {
 			panic(assertErr())
 		}
-		// Test the PENDING lock before acquiring a new SHARED lock.
-		if locked, _ := vfsOS.CheckPendingLock(file); locked {
-			return uint32(BUSY)
-		}
 		if rc := vfsOS.GetSharedLock(file, timeout); rc != _OK {
 			return uint32(rc)
 		}
@@ -195,11 +191,6 @@ func vfsCheckReservedLock(ctx context.Context, mod api.Module, pFile, pResOut ui
 	return uint32(rc)
 }
 
-func (vfsOSMethods) GetSharedLock(file *os.File, timeout time.Duration) xErrorCode {
-	// Acquire the SHARED lock.
-	return vfsOS.readLock(file, _SHARED_FIRST, _SHARED_SIZE, timeout)
-}
-
 func (vfsOSMethods) GetReservedLock(file *os.File, timeout time.Duration) xErrorCode {
 	// Acquire the RESERVED lock.
 	return vfsOS.writeLock(file, _RESERVED_BYTE, 1, timeout)
@@ -214,8 +205,3 @@ func (vfsOSMethods) CheckReservedLock(file *os.File) (bool, xErrorCode) {
 	// Test the RESERVED lock.
 	return vfsOS.checkLock(file, _RESERVED_BYTE, 1)
 }
-
-func (vfsOSMethods) CheckPendingLock(file *os.File) (bool, xErrorCode) {
-	// Test the PENDING lock.
-	return vfsOS.checkLock(file, _PENDING_BYTE, 1)
-}
diff --git a/vfs_os_unix.go b/vfs_os_unix.go
index 4f76194..28860d9 100644
--- a/vfs_os_unix.go
+++ b/vfs_os_unix.go
@@ -25,6 +25,15 @@ func (vfsOSMethods) Access(path string, flags _AccessFlag) error {
 	return unix.Access(path, access)
 }
 
+func (vfsOSMethods) GetSharedLock(file *os.File, timeout time.Duration) xErrorCode {
+	// Test the PENDING lock before acquiring a new SHARED lock.
+	if pending, _ := vfsOS.checkLock(file, _PENDING_BYTE, 1); pending {
+		return xErrorCode(BUSY)
+	}
+	// Acquire the SHARED lock.
+	return vfsOS.readLock(file, _SHARED_FIRST, _SHARED_SIZE, timeout)
+}
+
 func (vfsOSMethods) GetExclusiveLock(file *os.File, timeout time.Duration) xErrorCode {
 	if timeout == 0 {
 		timeout = time.Millisecond
diff --git a/vfs_os_windows.go b/vfs_os_windows.go
index 75df4fd..457ee55 100644
--- a/vfs_os_windows.go
+++ b/vfs_os_windows.go
@@ -63,6 +63,20 @@ func (vfsOSMethods) Allocate(file *os.File, size int64) error {
 	return file.Truncate(size)
 }
 
+func (vfsOSMethods) GetSharedLock(file *os.File, timeout time.Duration) xErrorCode {
+	// Acquire the PENDING lock temporarily before acquiring a new SHARED lock.
+	rc := vfsOS.readLock(file, _PENDING_BYTE, 1, timeout)
+
+	if rc == _OK {
+		// Acquire the SHARED lock.
+		rc = vfsOS.readLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
+
+		// Release the PENDING lock.
+		vfsOS.unlock(file, _PENDING_BYTE, 1)
+	}
+	return rc
+}
+
 func (vfsOSMethods) GetExclusiveLock(file *os.File, timeout time.Duration) xErrorCode {
 	if timeout == 0 {
 		timeout = time.Millisecond
@@ -74,8 +88,8 @@ func (vfsOSMethods) GetExclusiveLock(file *os.File, timeout time.Duration) xErro
 	// Acquire the EXCLUSIVE lock.
 	rc := vfsOS.writeLock(file, _SHARED_FIRST, _SHARED_SIZE, timeout)
 
-	// Reacquire the SHARED lock.
 	if rc != _OK {
+		// Reacquire the SHARED lock.
 		vfsOS.readLock(file, _SHARED_FIRST, _SHARED_SIZE, 0)
 	}
 	return rc