java.nio.*Buffer read/write atomicity (original) (raw)

Vitaly Davidovich vitalyd at gmail.com
Thu Dec 20 00:21:45 UTC 2012

I'm with David on this one - since BB specifically says that it's not threadsafe I don't see why there would be any expectation of atomicity. Same goes for IntBuffer or LongBuffer.

Vitaly

Sent from my phone On Dec 19, 2012 6:23 PM, "Zhong Yu" <zhong.j.yu at gmail.com> wrote:

Users are unlikely to expect multi-byte atomicity on a ByteBuffer.

However they are more likely to expect int-width atomicity on an IntBuffer view of a ByteBuffer; such atomicity is unfortunately not guaranteed either. Zhong Yu On Wed, Dec 19, 2012 at 11:48 AM, Aleksey Shipilev <aleksey.shipilev at oracle.com> wrote: > Hi guys, > > I wanted to cross-check what's the expected behavior of Buffers with > respect to atomicity? Don't confuse the atomic operations (a la > j.u.c.atomic.*) and the read/write atomicity. Here's the concrete > example, should the assert always be true? > > ByteBuffer buf = ByteBuffer.allocate(100); > (publish $buf to both threads properly) > (start both threads) > > Thread 1: > buf.putInt(0, 42); // at position 0 > > Thread 2: > int i = buf.getInt(0); // at position 0 > Assert.assertTrue( (i == 0) || (i == 42) ) > > Javadoc is silent about that, except for noting Buffers are not supposed > to be used from the multiple threads without synchronization. I would > anyway advocate to follow the atomicity behavior of plain fields and > arrays, and make these reads/writes atomic under the race. > > The apparent reason for at least BB to fail to be atomic is that we > read/write larger values byte-by-byte. Luckily, it appears to be easy to > fix (for a given endianness, we can just throw in the Unsafe call). > Before going out and submitting the RFE, I wanted to crosscheck if > somebody has strong feelings about this. > > Thanks, > Aleksey.

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