Currently on Linux we call system method pthread_self() to get current thread id:

  intx os::current_thread_id() { return (intx)pthread_self(); }

But pthread_self() returns pthread_t type which is defined
as unsigned long on Linux. As result we may truncate that value when
it is cast to (intx) in 32-bits VM.

But for some output (for example, Thread::print_on_error()) we use different
value thread->osthread()->thread_id(). Which is LWP id on Linux.
It's type is pid_t which is unsigned int.

Also defaultStream::hold() use INTX_FORMAT to print this id and
as result we can get negative values.

[kvn@intelsdv03 jvmg]$ fastdebug/bin/java -XX:AbortVMOnException=java.lang.NoClassDefFoundError -Xcomp -XX:+BackgroundCompilation -XX:CICompilerCount=8 -XX:+PrintCompilation t
VM option 'AbortVMOnException=java.lang.NoClassDefFoundError'
VM option '+BackgroundCompilation'
VM option 'CICompilerCount=8'
VM option '+PrintCompilation'
  1 java.lang.Thread::<init> (49 bytes)
  2 java.lang.System::getProperty (25 bytes)
  8 s! java.lang.ClassLoader::loadClass (58 bytes)
  7 java.lang.System::getSecurityManager (4 bytes)
  6 java.lang.String::lastIndexOf (12 bytes)
  5 s sun.misc.Launcher$AppClassLoader::loadClass (40 bytes)
  4 java.lang.ClassLoader::loadClass (7 bytes)
  3 s java.lang.ClassLoader::loadClassInternal (6 bytes)
--- n java.lang.ClassLoader::findLoadedClass0
--- n java.lang.ClassLoader::findBootstrapClass
--- n java.security.AccessController::doPrivileged (static)
--- n java.security.AccessController::doPrivileged (static)
--- n java.lang.Class::getPrimitiveClass (static)
# To suppress the following error report, specify this argument
# after -XX: or in .hotspotrc: SuppressErrorAt=/exceptions.cpp:378
#
# An unexpected error has been detected by Java Runtime Environment:
#
# Internal Error (/BUILD_AREA/jdk7/hotspot/src/share/vm/utilities/exceptions.cpp:378), pid=19034, tid=4160498576
# Error: Saw java.lang.NoClassDefFoundError, aborting
#
# Java VM: Java HotSpot(TM) Server VM (12.0-b01-fastdebug compiled mode linux-x86)
# An error report file with more information is saved as:
# /export/kvn/build/linux_amd64_compiler2/jvmg/hs_err_pid19034.log
#
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#
Current thread is 4160498576
Dumping core ...
Abort

[kvn@intelsdv03 jvmg]$ grep write hotspot.log
<writer thread='-1346954352'/>
<writer thread='-1346425968'/>
<writer thread='-1345369200'/>
<writer thread='-1344840816'/>
<writer thread='-1344312432'/>
<writer thread='-1343784048'/>
<writer thread='-1343255664'/>
<writer thread='-1345897584'/>
<writer thread='-134468720'/>

[kvn@intelsdv03 jvmg]$ cat hs_err_pid19034.log
#
# An unexpected error has been detected by Java Runtime Environment:
#
# Internal Error (/BUILD_AREA/jdk7/hotspot/src/share/vm/utilities/exceptions.cpp:378), pid=19034, tid=4160498576
# Error: Saw java.lang.NoClassDefFoundError, aborting
#
# Java VM: Java HotSpot(TM) Server VM (12.0-b01-fastdebug compiled mode linux-x86)
# If you would like to submit a bug report, please visit:
# http://java.sun.com/webapps/bugreport/crash.jsp
#

--------------- T H R E A D ---------------

Current thread (0x08063c00): JavaThread "main" [_thread_in_vm, id=19035, stack(0xf7f72000,0xf7fc3000)]

Stack: [0xf7f72000,0xf7fc3000], sp=0xf7fc1f00, free space=319k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [libjvm.so+0xb06c83]
V [libjvm.so+0x5becb5]
V [libjvm.so+0x61f6f9]
V [libjvm.so+0x61fdc2]
V [libjvm.so+0xa710e0]
V [libjvm.so+0xa70f4d]
V [libjvm.so+0x776f51]
V [libjvm.so+0x6cfe61]
C [libjli.so+0x4e17]
C [libjli.so+0x32d3] JavaMain+0x1d3
C [libpthread.so.0+0x52db]


--------------- P R O C E S S ---------------

Java Threads: ( => current thread )
  0x0821dc00 JavaThread "Low Memory Detector" daemon [_thread_blocked, id=19064, stack(0xafaa0000,0xafaf1000)]
  0x0821b400 JavaThread "CompilerThread7" daemon [_thread_in_native, id=19063, stack(0xafaf1000,0xafb72000)]
  0x08219400 JavaThread "CompilerThread6" daemon [_thread_in_native, id=19062, stack(0xafb72000,0xafbf3000)]
  0x08217400 JavaThread "CompilerThread5" daemon [_thread_blocked, id=19061, stack(0xafbf3000,0xafc74000)]
  0x08215000 JavaThread "CompilerThread4" daemon [_thread_in_native, id=19060, stack(0xafc74000,0xafcf5000)]
  0x08213000 JavaThread "CompilerThread3" daemon [_thread_in_native, id=19059, stack(0xafcf5000,0xafd76000)]
  0x08211000 JavaThread "CompilerThread2" daemon [_thread_in_native, id=19058, stack(0xafd76000,0xafdf7000)]
  0x0820f800 JavaThread "CompilerThread1" daemon [_thread_in_native, id=19057, stack(0xafdf7000,0xafe78000)]
  0x0820c000 JavaThread "CompilerThread0" daemon [_thread_blocked, id=19056, stack(0xafe78000,0xafef9000)]
  0x0820a400 JavaThread "Signal Dispatcher" daemon [_thread_blocked, id=19055, stack(0xafef9000,0xaff4a000)]
  0x081ee000 JavaThread "Finalizer" daemon [_thread_blocked, id=19054, stack(0xaff4a000,0xaff9b000)]
  0x081ec400 JavaThread "Reference Handler" daemon [_thread_blocked, id=19053, stack(0xaff9b000,0xaffec000)]
=>0x08063c00 JavaThread "main" [_thread_in_vm, id=19035, stack(0xf7f72000,0xf7fc3000)]

Other Threads:
  0x081e7400 VMThread [stack: 0xaffec000,0xb006d000] [id=19052]
  0xaf900800 WatcherThread [stack: 0xafa1f000,0xafaa0000] [id=19065]