block.cpp

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#include "block.h"
#include <sys/mman.h>
#include <throwcall.h>
 
block::block(size_t aBlockSize) :
    bytes(0),
    blockSize(aBlockSize),
    startOffset(0),
    hole(false) {
    buffer = throwcall::badval(mmap(nullptr, blockSize,
                                    PROT_READ | PROT_WRITE,
                                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0),
                               MAP_FAILED, "can't allocate buffer with size ", blockSize);
}
block::~block() {
    throwcall::good0(munmap(buffer, blockSize), "can't unmap buffer");
}
 
const void* block::bufferAt(size_t aOffset) const {
    if (__builtin_expect(hole, false)) {
        return nullBuffer();
    }
    return static_cast<const void*>(static_cast<char*>(buffer) + aOffset);
}
void* block::bufferAt(size_t aOffset)   {
    if (__builtin_expect(hole, false)) {
        throw std::runtime_error("non const bufferAt called for hole block");
    }
    return static_cast<void*>(static_cast<char*>(buffer) + aOffset);
}
size_t block::nullBufferSize() {
    return 1024 * 1024 * 16;
}
const void *block::nullBuffer() {
    static void* nullBuf = nullptr;
    if (nullBuf == nullptr) {
        nullBuf =  throwcall::badval(mmap(nullptr, nullBufferSize(),
                                          PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0),
                                     MAP_FAILED, "can't allocate buffer with size ", nullBufferSize());
        // according no mmap(2) the buffer is zero-filled
    }
    return nullBuf;
}