office-gobmx/include/jvmaccess/virtualmachine.hxx

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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 * This file incorporates work covered by the following license notice:
 *
 *   Licensed to the Apache Software Foundation (ASF) under one or more
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#ifndef INCLUDED_JVMACCESS_VIRTUALMACHINE_HXX
#define INCLUDED_JVMACCESS_VIRTUALMACHINE_HXX

#include <jvmaccess/jvmaccessdllapi.h>
#include <rtl/ref.hxx>
#include <salhelper/simplereferenceobject.hxx>

#if defined __clang__
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wunknown-attributes"
#endif
#include <jni.h>
#if defined __clang__
#pragma clang diagnostic pop
#endif

namespace jvmaccess
{
/** An encapsulating wrapper around a Java virtual machine.
 */
class JVMACCESS_DLLPUBLIC VirtualMachine final : public salhelper::SimpleReferenceObject
{
public:
    /** A helper to attach a thread to a Java virtual machine.

        @descr
        Upon construction of a guard the current thread is attached to the
        virtual machine, and upon destruction of the guard the thread is
        detached again.  For any one thread, multiple instances of this class
        may be used in a stack-like fashion (care is taken to only really
        detach the thread from the virtual machine upon destruction of the guard
        at the bottom of the stack).
     */
    class JVMACCESS_DLLPUBLIC AttachGuard
    {
    public:
        /** An exception indicating failure to create an AttachGuard.
         */
        class JVMACCESS_DLLPUBLIC CreationException final
        {
        public:
            CreationException();

            CreationException(CreationException const&);

            CreationException& operator=(CreationException const&);
        };

        /** Attach the current thread to a virtual machine.

            @param rMachine
            The virtual machine to attach to.  Must not be a null reference.

            @exception CreationException
            Thrown in case attaching fails (due to a JNI problem).
         */
        explicit AttachGuard(rtl::Reference<VirtualMachine> xMachine);

        /** Detach the current thread from the virtual machine again.
         */
        ~AttachGuard();

        /** Get a JNI environment pointer for the current thread.

            @return
            A valid JNI environment pointer.  Will never be null.
         */
        JNIEnv* getEnvironment() const { return m_pEnvironment; }

    private:
        AttachGuard(AttachGuard const&) = delete;
        AttachGuard& operator=(AttachGuard const&) = delete;

        rtl::Reference<VirtualMachine> m_xMachine;
        JNIEnv* m_pEnvironment;
        bool m_bDetach;
    };

    /** Create a wrapper around a Java virtual machine.

        @param pVm
        A JNI pointer to virtual machine.  Must not be null.

        @param nVersion
        The JNI version of the virtual machine pointed to by pVm.  Must be at
        least JNI_VERSION_1_2.  This parameter should be of type jint, not int,
        but at least on some platforms the definition of jint changed from
        JDK 1.3 (long) to JDK 1.4 (int), so that the mangled C++ name of the
        constructor would depend on the JDK version used at compile time.

        @param bDestroy
        Whether to destroy the virtual machine when destructing the wrapper
        (i.e., whether the wrapper owns the virtual machine pointed to by pVm).

        @param pMainThreadEnv
        A valid JNI environment pointer for the current thread; must not be
        null.  The current thread must be "initially attached" to the virtual
        machine while this constructor is being called (i.e., it must be the
        thread that has called JNI_CreateJavaVM in case the virtual machine has
        been started via the JNI Invocation API, and it must not already have
        called DetachCurrentThread; or it must be executing native code called
        from a "primordial" virtual machine).  This environment pointer was
        formerly used to obtain a reference to the thread's current context
        class loader (java.lang.Thread.getCurrentClassLoader; if later a native
        thread was attached to the virtual machine, that thread's context class
        loader would be null, so the AttachGuard first of all set it to the
        saved value; this feature has been removed again for performance reasons
        and because the default context class loader is often not useful, so
        that code relying on a context class loader has to set one explicitly,
        anyway).  This parameter is currently unused (but may be used again in
        the future).
     */
    VirtualMachine(JavaVM* pVm, int nVersion, bool bDestroy, JNIEnv const* pMainThreadEnv);

private:
    VirtualMachine(VirtualMachine const&) = delete;
    VirtualMachine& operator=(VirtualMachine const&) = delete;

    virtual ~VirtualMachine() override;

    JNIEnv* attachThread(bool* pAttached) const;

    void detachThread() const;

    JavaVM* m_pVm;
    jint m_nVersion;
    bool m_bDestroy;

    friend class AttachGuard; // to access attachThread, detachThread
};
}

#endif // INCLUDED_JVMACCESS_VIRTUALMACHINE_HXX

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