Stack dump shows we have 1056 threads running and many of them are piled up on an allocation lock:

Thread 1038 (Thread 0x7fd9d3276640 (LWP 657066)):
#0 0x00007fdba8487400 in __lll_lock_wait () from /lib64/libc.so.6
#1 0x00007fdba848d602 in pthread_mutex_lock@@GLIBC_2.2.5 () from /lib64/libc.so.6
#2 0x00007fdba7ef21e3 in Mutex::lock_contended(Thread*) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#3 0x00007fdba7ef22eb in Mutex::lock() () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#4 0x00007fdba7c943b7 in G1CollectedHeap::attempt_allocation_slow(unsigned int, unsigned long, bool) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#5 0x00007fdba7c94a49 in G1CollectedHeap::allocate_new_tlab(unsigned long, unsigned long, unsigned long*) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#6 0x00007fdba7eb1dc2 in MemAllocator::mem_allocate_inside_tlab_slow(MemAllocator::Allocation&) const () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#7 0x00007fdba7eb1f16 in MemAllocator::mem_allocate(MemAllocator::Allocation&) const () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#8 0x00007fdba7eb1fb9 in MemAllocator::allocate() const () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#9 0x00007fdba7d749c4 in InstanceKlass::allocate_instance(JavaThread*) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#10 0x00007fdba7d8dfd3 in InterpreterRuntime::_new(JavaThread*, ConstantPool*, int) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#11 0x00007fdba7b0363c in void BytecodeInterpreter::run<false, true>(BytecodeInterpreter*) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so
#12 0x00007fdba8088059 in ZeroInterpreter::main_loop(int, JavaThread*) () from /opt/mach5/mesos/work_dir/jib-master/install/jdk-26+25-2538/linux-x64-zero.jdk/jdk-26/lib/zero/libjvm.so