diff options
| -rw-r--r-- | lib/circular_buffer.cpp | 77 |
1 files changed, 62 insertions, 15 deletions
diff --git a/lib/circular_buffer.cpp b/lib/circular_buffer.cpp index 5e56469..979eefa 100644 --- a/lib/circular_buffer.cpp +++ b/lib/circular_buffer.cpp @@ -32,6 +32,58 @@ static std::string omg_so_unique(void) return boost::str(boost::format("shmem-%s-%u") % tid % count++); } +//! Round a number (length or address) to an IPC boundary +static size_t round_up_to_ipc_page(const size_t bytes) +{ + const size_t chunk = ipc::mapped_region::get_page_size(); + return chunk*((bytes + chunk - 1)/chunk); +} + +/*! + * OK, we need a chunk of virtual memory that can be mapped. + * But we cant actually be holding exclusive access to that memory + * until it it mapped... This is naturally a race condition. + */ +static void *probably_get_vmem(const size_t length) +{ + void *addr = NULL; + + /* + #if defined(linux) || defined(__linux) || defined(__linux__) + addr = mmap(NULL, length, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + munmap(addr, length); + return addr; + #endif + //*/ + + const std::string shm_name = omg_so_unique(); + + //std::cout << "make shmem 2x\n" << std::endl; + ipc::shared_memory_object shm_obj_2x( + ipc::create_only, //only create + shm_name.c_str(), //name + ipc::read_write //read-write mode + ); + + //std::cout << "truncate 2x\n" << std::endl; + shm_obj_2x.truncate(length); + + { + //std::cout << "map region 0\n" << std::endl; + ipc::mapped_region region0( + shm_obj_2x, //Memory-mappable object + ipc::read_write, //Access mode + 0, //Offset from the beginning of shm + length //Length of the region + ); + //std::cout << "region0.get_address() " << size_t(region0.get_address()) << std::endl; + addr = region0.get_address(); + } + + ipc::shared_memory_object::remove(shm_name.c_str()); + return addr; +} + struct CircularBuffer { CircularBuffer(const size_t); @@ -42,29 +94,24 @@ struct CircularBuffer } char *buff_addr; - size_t actual_length; + const size_t actual_length; std::string shm_name; ipc::shared_memory_object shm_obj; ipc::mapped_region region1; ipc::mapped_region region2; }; -CircularBuffer::CircularBuffer(const size_t num_bytes) +CircularBuffer::CircularBuffer(const size_t num_bytes): + buff_addr(NULL), + actual_length(round_up_to_ipc_page(num_bytes)) { boost::mutex::scoped_lock lock(alloc_mutex); - const size_t chunk = ipc::mapped_region::get_page_size(); - const size_t len = chunk*((num_bytes + chunk - 1)/chunk); - actual_length = len; - //////////////////////////////////////////////////////////////// // Step 0) Find an address that can be mapped across 2x length: //////////////////////////////////////////////////////////////// - { - ipc::mapped_region region0(ipc::anonymous_shared_memory(len*2)); - buff_addr = (char *)region0.get_address(); - } - std::cout << "reserve addr " << std::hex << size_t(buff_addr) << std::dec << std::endl; + buff_addr = (char *)probably_get_vmem(actual_length*2); + //std::cout << "reserve addr " << std::hex << size_t(buff_addr) << std::dec << std::endl; //////////////////////////////////////////////////////////////// // Step 1) Allocate a chunk of physical memory of length bytes @@ -78,7 +125,7 @@ CircularBuffer::CircularBuffer(const size_t num_bytes) ); //std::cout << "truncate\n" << std::endl; - shm_obj.truncate(len); + shm_obj.truncate(actual_length); //////////////////////////////////////////////////////////////// //Step 2) Remap region1 of the virtual memory space @@ -88,7 +135,7 @@ CircularBuffer::CircularBuffer(const size_t num_bytes) shm_obj, //Memory-mappable object ipc::read_write, //Access mode 0, //Offset from the beginning of shm - len, //Length of the region + actual_length, //Length of the region buff_addr ); //std::cout << "region1.get_address() " << size_t(region1.get_address()) << std::endl; @@ -101,8 +148,8 @@ CircularBuffer::CircularBuffer(const size_t num_bytes) shm_obj, //Memory-mappable object ipc::read_write, //Access mode 0, //Offset from the beginning of shm - len, //Length of the region - buff_addr + len + actual_length, //Length of the region + buff_addr + actual_length ); //std::cout << "region2.get_address() " << size_t(region2.get_address()) << std::endl; |