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*
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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package sun.tools.jstack;
import java.io.InputStream;
import java.util.Collection;
import com.sun.tools.attach.VirtualMachine;
import sun.tools.attach.HotSpotVirtualMachine;
import sun.tools.common.ProcessArgumentMatcher;
import sun.tools.common.PrintStreamPrinter;
/*
* This class is the main class for the JStack utility. It parses its arguments
* and decides if the command should be executed by the SA JStack tool or by
* obtained the thread dump from a target process using the VM attach mechanism
*/
public class JStack {
public static void main(String[] args) throws Exception {
if (args.length == 0) {
usage(1); // no arguments
}
checkForUnsupportedOptions(args);
boolean locks = false;
boolean extended = false;
// Parse the options (arguments starting with "-" )
int optionCount = 0;
while (optionCount < args.length) {
String arg = args[optionCount];
if (!arg.startsWith("-")) {
break;
}
if (arg.equals("-?") ||
arg.equals("-h") ||
arg.equals("--help") ||
// -help: legacy.
arg.equals("-help")) {
usage(0);
}
else {
if (arg.equals("-l")) {
locks = true;
} else {
if (arg.equals("-e")) {
extended = true;
} else {
usage(1);
}
}
}
optionCount++;
}
// Next we check the parameter count.
int paramCount = args.length - optionCount;
if (paramCount != 1) {
usage(1);
}
// pass -l to thread dump operation to get extra lock info
String pidArg = args[optionCount];
String params[]= new String[] { "" };
if (extended) {
params[0] += "-e ";
}
if (locks) {
params[0] += "-l";
}
ProcessArgumentMatcher ap = new ProcessArgumentMatcher(pidArg);
Collection<String> pids = ap.getVirtualMachinePids(JStack.class);
if (pids.isEmpty()) {
System.err.println("Could not find any processes matching : '" + pidArg + "'");
System.exit(1);
}
for (String pid : pids) {
if (pids.size() > 1) {
System.out.println("Pid:" + pid);
}
runThreadDump(pid, params);
}
}
// Attach to pid and perform a thread dump
private static void runThreadDump(String pid, String args[]) throws Exception {
VirtualMachine vm = null;
try {
vm = VirtualMachine.attach(pid);
} catch (Exception x) {
String msg = x.getMessage();
if (msg != null) {
System.err.println(pid + ": " + msg);
} else {
x.printStackTrace();
}
System.exit(1);
}
// Cast to HotSpotVirtualMachine as this is implementation specific
// method.
InputStream in = ((HotSpotVirtualMachine)vm).remoteDataDump((Object[])args);
// read to EOF and just print output
PrintStreamPrinter.drainUTF8(in, System.out);
vm.detach();
}
private static void checkForUnsupportedOptions(String[] args) {
// Check arguments for -F, -m, and non-numeric value
// and warn the user that SA is not supported anymore
int paramCount = 0;
for (String s : args) {
if (s.equals("-F")) {
SAOptionError("-F option used");
}
if (s.equals("-m")) {
SAOptionError("-m option used");
}
if (! s.startsWith("-")) {
paramCount += 1;
}
}
if (paramCount > 1) {
SAOptionError("More than one non-option argument");
}
}
private static void SAOptionError(String msg) {
System.err.println("Error: " + msg);
System.err.println("Cannot connect to core dump or remote debug server. Use jhsdb jstack instead");
System.exit(1);
}
// print usage message
private static void usage(int exit) {
System.err.println("Usage:");
System.err.println(" jstack [-l][-e] <pid>");
System.err.println(" (to connect to running process)");
System.err.println("");
System.err.println("Options:");
System.err.println(" -l long listing. Prints additional information about locks");
System.err.println(" -e extended listing. Prints additional information about threads");
System.err.println(" -? -h --help -help to print this help message");
System.exit(exit);
}
}
// Attach to pid and perform a thread dump
private static void runThreadDump(String pid, String args[]) throws Exception {
VirtualMachine vm = null;
try {
vm = VirtualMachine.attach(pid);
} catch (Exception x) {
String msg = x.getMessage();
if (msg != null) {
System.err.println(pid + ": " + msg);
} else {
x.printStackTrace();
}
System.exit(1);
}
// Cast to HotSpotVirtualMachine as this is implementation specific
// method.
InputStream in = ((HotSpotVirtualMachine)vm).remoteDataDump((Object[])args);
// read to EOF and just print output
PrintStreamPrinter.drainUTF8(in, System.out);
vm.detach();
}如上的核心实现，是通过 VirtualMachine 进行远程连接。
然后构建 JDK 源码通过 OpenJDK with CLion 懒人包 ，debug
依次
javaVFrame::print_locked_object_class_name vframe.cpp:1566javaVFrame::print_lock_info_on vframe.cpp:251JavaThread::print_stack_on thread.cpp:3259Threads::print_on thread.cpp:4786VM_PrintThreads::doit vmOperations.cpp:171VM_Operation::evaluate vmOperations.cpp:68VMThread::evaluate_operation vmThread.cpp:383VMThread::loop vmThread.cpp:521VMThread::run vmThread.cpp:274Thread::call_run thread.cpp:393thread_native_entry os_linux.cpp:791start_thread 0x00007fa45e0defa3clone 0x00007fa45e00a4cf
其中会创建 vframe.cpp#MonitorInfo
private:
oop _owner; // the object owning the monitor
BasicLock* _lock;
oop _owner_klass; // klass (mirror) if owner was scalar replaced
bool _eliminated;
bool _owner_is_scalar_replaced;然后会获取监听器的 owner
print_locked_object_class_name(st, Handle(THREAD, monitor->owner()), lock_state);最后通过 globalDefineitions.hpp#p2i 将 pointer 转化位 intptr_t
st->print("\t- %s <" INTPTR_FORMAT "> ", lock_state, p2i(obj()));
// Convert pointer to intptr_t, for use in printing pointers.
inline intptr_t p2i(const void * p) {
return (intptr_t) p;
}参见
"main" #1 prio=5 os_prio=31 tid=0x00007f9bd6808800 nid=0x1503 waiting on condition [0x000070000f70b000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(Native Method)
at Gzip3Test.main(Gzip3Test.java:22)
// 这里的值
- locked <0x000000071575ca20> (a java.lang.Object)
可以知道，最后打出来的值是锁的持有对象的地址。
通过 2023-08-2JOL 依赖类库 这个依赖库，也能获取到相对应的 10 进制值，然后转化成 16 进制即可发现一致。
比如
VM.current().addressOf(object);
-> 30423750320
-> 0x00000007156596b0和之前的 Synchronized 预期一致