Problem Description :
Customer has reported an issue , hang in preClose() method.
Analysis & Observation :
The preClose() method internally calls the dup2() system call. If there is a
dup2() call on a file descriptor on a thread while another thread is blocked in
a read/write operation on the same file descriptor, then the dup2() call is
known to hang. Currently, preClose() experiences a hang because we call dup2()
before killing the reader/writer thread(s).
Suggested Solution:
The solution is to first kill the reader/writer thread(s) and then do the
preClose() sequence. This reordering in the different channel implementations
resolves the customer problem as per the testing.
// wait for any outstanding read to complete
if (blocking) {
synchronized (stateLock) {
assert state == ST_CLOSING;
long th = thread;
if (th != 0) {
nd.preClose(fd);
NativeThread.signal(th);
The above code is changed to
// wait for any outstanding read to complete
if (blocking) {
synchronized (stateLock) {
assert state == ST_CLOSING;
long th = thread;
if (th != 0) {
NativeThread.signal(th);
nd.preClose(fd);
Releases:
OpenJDK11 & OpenJDK17 the issue is seen. In OpenJDK21 the issue is not seen.
Next steps:
We want to take the above mentioned fix to OpenJDK but unfortunately we are
seeing the below issue.
* The customer has confirmed that the issue is not reproducible in OpenJDK dev
branch
* We have not been successful in creating a java reproducer even after spending
a considerable amount of time.
Please review and suggest if the above understanding is right and we shall take
the fix to OpenJDK17 and backport to OpenJDK11.
