void
nsPipe::AdvanceReadCursor(PRUint32 bytesRead)
{
NS_ASSERTION(bytesRead, "dont call if no bytes read");
nsPipeEvents events;
{
nsAutoMonitor mon(mMonitor);
LOG(("III advancing read cursor by %u\n", bytesRead));
NS_ASSERTION(bytesRead <= mBuffer.GetSegmentSize(), "read too much");
mReadCursor += bytesRead;
NS_ASSERTION(mReadCursor <= mReadLimit, "read cursor exceeds limit");
mInput.ReduceAvailable(bytesRead);
if (mReadCursor == mReadLimit) {
// we've reached the limit of how much we can read from this segment.
// if at the end of this segment, then we must discard this segment.
// if still writing in this segment then bail because we're not done
// with the segment and have to wait for now...
if (mWriteSegment == 0 && mWriteLimit > mWriteCursor) {
NS_ASSERTION(mReadLimit == mWriteCursor, "unexpected state");
return;
}
// shift write segment index (-1 indicates an empty buffer).
--mWriteSegment;
// done with this segment
mBuffer.DeleteFirstSegment();
LOG(("III deleting first segment\n"));
if (mWriteSegment == -1) {
// buffer is completely empty
mReadCursor = nsnull;
mReadLimit = nsnull;
mWriteCursor = nsnull;
mWriteLimit = nsnull;
}
else {
// advance read cursor and limit to next buffer segment
mReadCursor = mBuffer.GetSegment(0);
if (mWriteSegment == 0)
mReadLimit = mWriteCursor;
else
mReadLimit = mReadCursor + mBuffer.GetSegmentSize();
}
// we've free'd up a segment, so notify output stream that pipe has
// room for a new segment.
if (mOutput.OnOutputWritable(events))
mon.Notify();
}
}
}
void
nsPipe::AdvanceWriteCursor(PRUint32 bytesWritten)
{
NS_ASSERTION(bytesWritten, "don't call if no bytes written");
nsPipeEvents events;
{
MonitorAutoEnter mon(mMonitor);
LOG(("OOO advancing write cursor by %u\n", bytesWritten));
char *newWriteCursor = mWriteCursor + bytesWritten;
NS_ASSERTION(newWriteCursor <= mWriteLimit, "write cursor exceeds limit");
// update read limit if reading in the same segment
if (mWriteSegment == 0 && mReadLimit == mWriteCursor)
mReadLimit = newWriteCursor;
mWriteCursor = newWriteCursor;
// The only way mReadCursor == mWriteCursor is if:
//
// - mReadCursor is at the start of a segment (which, based on how
// nsSegmentedBuffer works, means that this segment is the "first"
// segment)
// - mWriteCursor points at the location past the end of the current
// write segment (so the current write filled the current write
// segment, so we've incremented mWriteCursor to point past the end
// of it)
// - the segment to which data has just been written is located
// exactly one segment's worth of bytes before the first segment
// where mReadCursor is located
//
// Consequently, the byte immediately after the end of the current
// write segment is the first byte of the first segment, so
// mReadCursor == mWriteCursor. (Another way to think about this is
// to consider the buffer architecture diagram above, but consider it
// with an arena allocator which allocates from the *end* of the
// arena to the *beginning* of the arena.)
NS_ASSERTION(mReadCursor != mWriteCursor ||
(mBuffer.GetSegment(0) == mReadCursor &&
mWriteCursor == mWriteLimit),
"read cursor is bad");
// update the writable flag on the output stream
if (mWriteCursor == mWriteLimit) {
if (mBuffer.GetSize() >= mBuffer.GetMaxSize())
mOutput.SetWritable(PR_FALSE);
}
// notify input stream that pipe now contains additional data
if (mInput.OnInputReadable(bytesWritten, events))
mon.Notify();
}
}
void
nsPipe::PeekSegment(PRUint32 index, char *&cursor, char *&limit)
{
if (index == 0) {
NS_ASSERTION(!mReadCursor || mBuffer.GetSegmentCount(), "unexpected state");
cursor = mReadCursor;
limit = mReadLimit;
}
else {
PRUint32 numSegments = mBuffer.GetSegmentCount();
if (index >= numSegments)
cursor = limit = nsnull;
else {
cursor = mBuffer.GetSegment(index);
if (mWriteSegment == (PRInt32) index)
limit = mWriteCursor;
else
limit = cursor + mBuffer.GetSegmentSize();
}
}
}
nsresult
nsPipe::GetWriteSegment(char *&segment, PRUint32 &segmentLen)
{
nsAutoMonitor mon(mMonitor);
if (NS_FAILED(mStatus))
return mStatus;
// write cursor and limit may both be null indicating an empty buffer.
if (mWriteCursor == mWriteLimit) {
char *seg = mBuffer.AppendNewSegment();
// pipe is full
if (seg == nsnull)
return NS_BASE_STREAM_WOULD_BLOCK;
LOG(("OOO appended new segment\n"));
mWriteCursor = seg;
mWriteLimit = mWriteCursor + mBuffer.GetSegmentSize();
++mWriteSegment;
}
// make sure read cursor is initialized
if (mReadCursor == nsnull) {
NS_ASSERTION(mWriteSegment == 0, "unexpected null read cursor");
mReadCursor = mReadLimit = mWriteCursor;
}
// check to see if we can roll-back our read and write cursors to the
// beginning of the current/first segment. this is purely an optimization.
if (mReadCursor == mWriteCursor && mWriteSegment == 0) {
char *head = mBuffer.GetSegment(0);
LOG(("OOO rolling back write cursor %u bytes\n", mWriteCursor - head));
mWriteCursor = mReadCursor = mReadLimit = head;
}
segment = mWriteCursor;
segmentLen = mWriteLimit - mWriteCursor;
return NS_OK;
}