try_enqueue failed: moodycamel::ConcurrentQueue<signature_business_element, moodycamel::ConcurrentQueueDefaultTraits>::get_or_add_implicit_producer ( this=0x0) at ../common/multqueue.h:3313

[kdtiankong]

one procuder thread to put task to queue, muitiple comsumer to get tasks from queue,the queue is managered by shared_ptr, and the queue is created by std::make_shared and queue size is 1024*1024， when method try_enqueue was called,try_enqueue failed.of course, it occured once in a while，I do not know that how to solve it。
operation environment :centos7 x64
gcc version 4.8.5 20150623 (Red Hat 4.8.5-36) (GCC)。

[cameron314]

It's normal for try_enqueue to fail if it would otherwise require allocating memory to succeed.

The queue stores elements in blocks internally. The default block size (controllable through the traits) is 32. Each implicit producer (such as the one you're using) has an internal index to its allocated blocks. This index is large enough to address 32 blocks by default (so, 1024 elements total). After that, the index needs resizing, which requires allocating memory, which causes try_enqueue to fail.

I suggest providing traits that better match your use case. A BLOCK_SIZE of 1024 and IMPLICIT_INITIAL_INDEX_SIZE of 1024 should do the trick.

[kdtiankong]

@cameron314,what do you mean is that the default block size (controllable through the traits) is 32，the free-lock queue max size is 1024 ? If I want to enqueue more element, would I set variable BLOCK_SIZE and IMPLICIT_INITIAL_INDEX_SIZE larger(must be a power of 2)? If i use enqueue function to push element, the problem can be solved(As you can see from the documentation, enqueue and try_enqueue are allocated differently. )? Sorry, I know very little about this library principle.
Looking forward to your reply!

[cameron314]

enqueue and try_enqueue work the same way, except that try_enqueue is not allowed to allocate memory.

There are additional internal data structures that resize automatically by allocating more memory, but when using try_enqueue must be sized sufficiently from the start. The traits control these default sizes.

[cameron314]

For example, use something like the following to initialize your queue:

struct MegaImplicitTraits : moodycamel::ConcurrentQueueDefaultTraits {
    size_t BLOCK_SIZE = 1024;
    size_t IMPLICIT_INITIAL_INDEX_SIZE = 1024;
};
moodycamel::ConcurrentQueue<signature_business_element, MegaImplicitTraits> queue(1024*1024, 0, 1);

[kdtiankong]

Is BLOCK_SIZE one element size(power of 2)? is IMPLICIT_INITIAL_INDEX_SIZE means queues max size?

[cameron314]

BLOCK_SIZE is the number of elements in each internal block. Each enqueued element gets stored in a block.

IMPLICIT_INITIAL_INDEX_SIZE is the nunber of full blocks that can be contained by an implicit producer by default. Normally this simply grows as needed but try_enqueue prevents this, so it must be sized appropriately to begin with.

An implicit producer is a thread that enqueues without a producer token.

[cameron314]

Just noticed the this=0 in your stack trace. It seems your code is calling try_enqueue on a null pointer instead of a ConcurrentQueue object, which would explain a segfault.

[kdtiankong]

Thank you very much!!

[rafal98]

Hi, just to inform that now, it seems you should do this:

struct MegaImplicitTraits : moodycamel::ConcurrentQueueDefaultTraits {
    **static const** size_t BLOCK_SIZE = 1024;
    **static const** size_t IMPLICIT_INITIAL_INDEX_SIZE = 1024;
};

And I confirm that limitation is no more 1024, but 1048576.

Thx for this great code