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/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* 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.
*/
package com.android.internal.os;
import com.android.internal.util.ProcFileReader;
import java.io.FileInputStream;
import java.io.IOException;
/**
* Reads and parses {@code locks} files in the {@code proc} filesystem.
* A typical example of /proc/locks
*
* 1: POSIX ADVISORY READ 18403 fd:09:9070 1073741826 1073742335
* 2: POSIX ADVISORY WRITE 18292 fd:09:34062 0 EOF
* 2: -> POSIX ADVISORY WRITE 18291 fd:09:34062 0 EOF
* 2: -> POSIX ADVISORY WRITE 18293 fd:09:34062 0 EOF
* 3: POSIX ADVISORY READ 3888 fd:09:13992 128 128
* 4: POSIX ADVISORY READ 3888 fd:09:14230 1073741826 1073742335
*/
public class ProcLocksReader {
private final String mPath;
private ProcFileReader mReader = null;
public ProcLocksReader() {
mPath = "/proc/locks";
}
public ProcLocksReader(String path) {
mPath = path;
}
/**
* This interface is for AMS to run callback function on every processes one by one
* that hold file locks blocking other processes.
*/
public interface ProcLocksReaderCallback {
/**
* Call the callback function of handleBlockingFileLocks().
* @param pid Each process that hold file locks blocking other processes.
*/
void onBlockingFileLock(int pid);
}
/**
* Checks if a process corresponding to a specific pid owns any file locks.
* @param callback Callback function, accepting pid as the input parameter.
* @throws IOException if /proc/locks can't be accessed or correctly parsed.
*/
public void handleBlockingFileLocks(ProcLocksReaderCallback callback) throws IOException {
long last = -1;
long id; // ordinal position of the lock in the list
int owner = -1; // the PID of the process that owns the lock
int pid = -1; // the PID of the process blocking others
if (mReader == null) {
mReader = new ProcFileReader(new FileInputStream(mPath));
} else {
mReader.rewind();
}
while (mReader.hasMoreData()) {
id = mReader.nextLong(true); // lock id
if (id == last) {
mReader.finishLine(); // blocked lock
if (pid < 0) {
pid = owner; // get pid from the previous line
callback.onBlockingFileLock(pid);
}
continue;
} else {
pid = -1; // a new lock
}
mReader.nextIgnored(); // lock type: POSIX?
mReader.nextIgnored(); // lock type: MANDATORY?
mReader.nextIgnored(); // lock type: RW?
owner = mReader.nextInt(); // pid
mReader.finishLine();
last = id;
}
}
}
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