C++ blocking queue can't poll current data - c++

Question

I have faced an odd situation.
I have a android app which calls C++ code.
In C++ code, I have two thread one is putting data into a blocking queue and another thread is taking data out of blocking queue.
The data structure is like:
typedef struct {
int len;
char* data;
} myStruct;
Every time I will put a pointer of myStruct into the queue and get this pointer out of the queue.
But sometime I will get a very big len from the data. like the log file I showed below:
Put Log Length: 128
Take Log Length: 128
Put Log Length: 171
Take Log Length: 171
Put Log Length: 73
Take Log Length: 73
Put Length: 99
Put Length: 72
Put Length: 124
Take Log Length: 72
......
Take Log Length: 2047249896
My Blocking Queue code is list below:
#include "BlockingQueue.h"
template<typename T>
void BlockingQueue<T>::put(const T& task)
{
std::unique_lock<std::mutex> lock(mtx);
q.push_back( task );
isEmpty.notify_all();
}
template<typename T>
T BlockingQueue<T>::take()
{
std::unique_lock<std::mutex> lock(mtx);
isEmpty.wait(lock, [this]{return !q.empty(); });
T front( q.front() );
q.pop_front();
return front;
}
template<typename T>
bool BlockingQueue<T>::empty()
{
std::unique_lock<std::mutex> lock(mtx);
return q.empty();
}