spsc_queue::pop(OutputIterator it) improperly works with random-access iterators if the read pointer is bigger than the write pointer (stored data consists of 2 blocks)

[Constantin Fishkin <constantin_fishkin@…>]

spsc_queue::pop(OutputIterator it) method improperly works with random-access iterators if the queue's read pointer is bigger than the queue's write pointer (the queue's stored data consists of 2 blocks)

The following code will fill dst array improperly if the queue's read pointer is bigger than the queue's write pointer:

unsigned char* dst=new unsigned char[100];

count=q.pop(dst);

The bug caused by the code in spsc_queue.hpp:224:

std::copy(internal_buffer+read_index, internal_buffer+max_size, it);

std::copy(internal_buffer, internal_buffer+count1, it);

It will copy the second fragment starting from the same point it copied the first ftagment. The problem can be fixed as:

it=std::copy(internal_buffer+read_index, internal_buffer+max_size, it);

std::copy(internal_buffer, internal_buffer+count1, it);

[Constantin Fishkin <constantin_fishkin@…>]

test that demonstrates the bug

[timblechmann]

good point ... but can you upload a working test case? will have a look at the code this night ...

[Constantin Fishkin <constantin_fishkin@…>]

this time proper file

[Constantin Fishkin <constantin_fishkin@…>]

Replying to timblechmann:

good point ... but can you upload a working test case? will have a look at the code this night ...

Oops, sorry. Please have a look at test.cpp

[timblechmann]

(In [84571]) lockfree: spsc-queue - correct dequeue to output iterator

fixes #8629

Signed-off-by: Tim Blechmann <tim@…>