bytedeco/javacpp

The same function pointer set more than 10 times will always pass in a NULL pointer to C/C++

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#611 opened on Sep 29, 2022

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Description

Hi @saudet ,

As the subject mentioned, I suspect this is a bug. In C, the code is like:

#include <iostream>
#include "RpcImpl.h"

using namespace std;
namespace client {
    rpc_handler_t handler;

    void ClientSetMessageHandler(rpc_handler_t userHandler) {
        RPC_INFO("ClientSetMessageHandler userHandler:%p", userHandler);
        handler = userHandler;
    }
}

In Java/Kotlin we got:

@RunWith(AndroidJUnit4::class)
class TestShotSync {

    @Test
    fun testFunctionPointer() {
        for (i in 1..20) {
            val handler = ShotSync.rpc_handler_t()
            println("ClientSetMessageHandler No. $i $handler")
            ShotSync.ClientSetMessageHandler(handler)
        }
    }
}

And after we run the code, the output is like:

2022-09-29 10:03:55.010 9271-9294 I/System.out: ClientSetMessageHandler No. 1 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433170,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433170,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.011 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1ecdd
2022-09-29 10:03:55.011 9271-9294 I/System.out: ClientSetMessageHandler No. 2 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433180,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433180,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.011 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f015
2022-09-29 10:03:55.012 9271-9294 I/System.out: ClientSetMessageHandler No. 3 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433188,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433188,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.012 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f035
2022-09-29 10:03:55.013 9271-9294 I/System.out: ClientSetMessageHandler No. 4 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433190,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433190,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.013 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f055
2022-09-29 10:03:55.013 9271-9294 I/System.out: ClientSetMessageHandler No. 5 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433198,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433198,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.013 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f075
2022-09-29 10:03:55.014 9271-9294 I/System.out: ClientSetMessageHandler No. 6 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331a0,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331a0,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.014 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f095
2022-09-29 10:03:55.015 9271-9294 I/System.out: ClientSetMessageHandler No. 7 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331a8,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331a8,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.015 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f0b5
2022-09-29 10:03:55.015 9271-9294 I/System.out: ClientSetMessageHandler No. 8 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331b0,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331b0,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.015 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f0d5
2022-09-29 10:03:55.016 9271-9294 I/System.out: ClientSetMessageHandler No. 9 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331b8,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331b8,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.016 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f0f5
2022-09-29 10:03:55.017 9271-9294 I/System.out: ClientSetMessageHandler No. 10 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331c0,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331c0,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.017 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0xced1f115
2022-09-29 10:03:55.018 9271-9294 I/System.out: ClientSetMessageHandler No. 11 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331c8,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331c8,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.018 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.018 9271-9294 I/System.out: ClientSetMessageHandler No. 12 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331d0,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331d0,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.018 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.020 9271-9294 I/System.out: ClientSetMessageHandler No. 13 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331d8,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331d8,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.020 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.020 9271-9294 I/System.out: ClientSetMessageHandler No. 14 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331e0,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331e0,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.020 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.021 9271-9294 I/System.out: ClientSetMessageHandler No. 15 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331e8,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331e8,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.021 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.022 9271-9294 I/System.out: ClientSetMessageHandler No. 16 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331f0,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331f0,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.022 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.023 9271-9294 I/System.out: ClientSetMessageHandler No. 17 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe44331f8,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe44331f8,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.023 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.024 9271-9294 I/System.out: ClientSetMessageHandler No. 18 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433200,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433200,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.024 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.025 9271-9294 I/System.out: ClientSetMessageHandler No. 19 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433208,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433208,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.025 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0
2022-09-29 10:03:55.026 9271-9294 I/System.out: ClientSetMessageHandler No. 20 com.senter.shotsync.ShotSync$rpc_handler_t[address=0xe4433210,position=0,limit=1,capacity=1,deallocator=org.bytedeco.javacpp.Pointer$NativeDeallocator[ownerAddress=0xe4433210,deallocatorAddress=0xced1f8d1]]
2022-09-29 10:03:55.026 9271-9294 I/[STC-RPC]: ClientSetMessageHandler userHandler:0x0

As we can see, after 10 times of setting the function pointer, we always got a NULL one in C.

The patch to reproduce it is here.

Is this because we have only 10 instances of the function pointer in JNI?

Contributor guide

Research direction
Trace the JNI function pointer allocation in the C++ code to find why after 10 allocations the pointer becomes NULL. Check the pool size or caching mechanism.
Tech stack
javacpp
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
JavaC/C++JNI
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60