fix flock() bug on ashmem in Android

2026-10-26 02:17:25 +08:00 · 2019-12-30 21:21:42 +08:00
parent 7174bf9603
commit 3c61c8ea2c
15 changed files with 160 additions and 33 deletions
@@ -0,0 +1,89 @@
+/*
+ * Tencent is pleased to support the open source community by making
+ * MMKV available.
+ *
+ * Copyright (C) 2019 THL A29 Limited, a Tencent company.
+ * All rights reserved.
+ *
+ * Licensed under the BSD 3-Clause License (the "License"); you may not use
+ * this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ *       https://opensource.org/licenses/BSD-3-Clause
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "InterProcessLock.h"
+
+#ifdef MMKV_ANDROID
+#    include "MMKVLog.h"
+#    include <sys/file.h>
+#    include <unistd.h>
+
+namespace mmkv {
+
+FileLock::FileLock(MMKV_FILE_HANDLE fd, bool isAshmem)
+    : m_fd(fd), m_sharedLockCount(0), m_exclusiveLockCount(0), m_isAshmem(isAshmem) {
+    m_lockInfo.l_type = F_WRLCK;
+    m_lockInfo.l_start = 0;
+    m_lockInfo.l_whence = SEEK_SET;
+    m_lockInfo.l_len = 0;
+    m_lockInfo.l_pid = 0;
+}
+
+static short LockType2FlockType(LockType lockType) {
+    switch (lockType) {
+        case SharedLockType:
+            return F_RDLCK;
+        case ExclusiveLockType:
+            return F_WRLCK;
+    }
+}
+
+bool FileLock::ashmemLock(LockType lockType, bool wait, bool unLockFirstIfNeeded) {
+    m_lockInfo.l_type = LockType2FlockType(lockType);
+    if (unLockFirstIfNeeded) {
+        // try lock
+        auto ret = fcntl(m_fd, F_SETLK, &m_lockInfo);
+        if (ret == 0) {
+            return true;
+        }
+        // lets be gentleman: unlock my shared-lock to prevent deadlock
+        auto type = m_lockInfo.l_type;
+        m_lockInfo.l_type = F_UNLCK;
+        ret = fcntl(m_fd, F_SETLK, &m_lockInfo);
+        if (ret != 0) {
+            MMKVError("fail to try unlock first fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
+        }
+        m_lockInfo.l_type = type;
+    }
+
+    int cmd = wait ? F_SETLKW : F_SETLK;
+    auto ret = fcntl(m_fd, cmd, &m_lockInfo);
+    if (ret != 0) {
+        MMKVError("fail to lock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
+        return false;
+    } else {
+        return true;
+    }
+}
+
+bool FileLock::ashmemUnLock(bool unlockToSharedLock) {
+    m_lockInfo.l_type = static_cast<short>(unlockToSharedLock ? F_RDLCK : F_UNLCK);
+    auto ret = fcntl(m_fd, F_SETLK, &m_lockInfo);
+    if (ret != 0) {
+        MMKVError("fail to unlock fd=%d, ret=%d, error:%s", m_fd, ret, strerror(errno));
+        return false;
+    } else {
+        return true;
+    }
+}
+
+} // namespace mmkv
+
+#endif // MMKV_ANDROID