libutils/include/utils/Thread.h

/*
 * Copyright (C) 2007 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.
 */

#ifndef _LIBS_UTILS_THREAD_H
#define _LIBS_UTILS_THREAD_H

#include <stdint.h>
#include <sys/types.h>
#include <time.h>

#if !defined(_WIN32)
# include <pthread.h>
#endif

#include <utils/Condition.h>
#include <utils/Errors.h>
#include <utils/Mutex.h>
#include <utils/RefBase.h>
#include <utils/Timers.h>
#include <utils/ThreadDefs.h>

// ---------------------------------------------------------------------------
namespace android {
// ---------------------------------------------------------------------------

// DO NOT USE: please use std::thread

class Thread : virtual public RefBase
{
public:
    // Create a Thread object, but doesn't create or start the associated
    // thread. See the run() method. This object must be used with RefBase/sp,
    // like any other RefBase object, because they are conventionally promoted
    // from bare pointers (Thread::run is particularly problematic here).
    explicit            Thread(bool canCallJava = true);
    virtual             ~Thread();

    // Start the thread in threadLoop() which needs to be implemented.
    // NOLINTNEXTLINE(google-default-arguments)
    virtual status_t    run(    const char* name,
                                int32_t priority = PRIORITY_DEFAULT,
                                size_t stack = 0);
    
    // Ask this object's thread to exit. This function is asynchronous, when the
    // function returns the thread might still be running. Of course, this
    // function can be called from a different thread.
    virtual void        requestExit();

    // Good place to do one-time initializations
    virtual status_t    readyToRun();
    
    // Call requestExit() and wait until this object's thread exits.
    // BE VERY CAREFUL of deadlocks. In particular, it would be silly to call
    // this function from this object's thread. Will return WOULD_BLOCK in
    // that case.
            status_t    requestExitAndWait();

    // Wait until this object's thread exits. Returns immediately if not yet running.
    // Do not call from this object's thread; will return WOULD_BLOCK in that case.
            status_t    join();

    // Indicates whether this thread is running or not.
            bool        isRunning() const;

#if defined(__ANDROID__)
    // Return the thread's kernel ID, same as the thread itself calling gettid(),
    // or -1 if the thread is not running.
            pid_t       getTid() const;
#endif

protected:
    // exitPending() returns true if requestExit() has been called.
            bool        exitPending() const;
    
private:
    // Derived class must implement threadLoop(). The thread starts its life
    // here. There are two ways of using the Thread object:
    // 1) loop: if threadLoop() returns true, it will be called again if
    //          requestExit() wasn't called.
    // 2) once: if threadLoop() returns false, the thread will exit upon return.
    virtual bool        threadLoop() = 0;

private:
    Thread& operator=(const Thread&);
    static  int             _threadLoop(void* user);
    const   bool            mCanCallJava;
    // always hold mLock when reading or writing
            thread_id_t     mThread;
    mutable Mutex           mLock;
            Condition       mThreadExitedCondition;
            status_t        mStatus;
    // note that all accesses of mExitPending and mRunning need to hold mLock
    volatile bool           mExitPending;
    volatile bool           mRunning;
            sp<Thread>      mHoldSelf;
#if defined(__ANDROID__)
    // legacy for debugging, not used by getTid() as it is set by the child thread
    // and so is not initialized until the child reaches that point
            pid_t           mTid;
#endif
};

}  // namespace android

// ---------------------------------------------------------------------------
#endif // _LIBS_UTILS_THREAD_H
// ---------------------------------------------------------------------------