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Java Forum / General / August 2006Do I get Physical Thread in Java?
When you write Thread t = new MyThread(); r.start(), do you get a new thread (you know like in Linux you call pthread_create() and kernel gives you a new thread for running). Maybe java is optimizing and JVM will not call pthread_create when you new your thrread? If anyone know, please explain; thank you. > When you write Thread t = new MyThread(); r.start(), do you get a new > thread (you know like in Linux you call pthread_create() and kernel > gives you a new thread for running). Maybe java is optimizing and JVM > will not call pthread_create when you new your thrread? > > If anyone know, please explain; thank you. This is up to the JVM implementation. The Java standard decribess how threads behave, but whether they're implemented with OS-level threads, a lightweight threading package, or by having a single-threaded interpreter round-robin among the active threads is left open. >> When you write Thread t = new MyThread(); r.start(), do you get a new >> thread (you know like in Linux you call pthread_create() and kernel [quoted text clipped - 7 lines] > a lightweight threading package, or by having a single-threaded > interpreter round-robin among the active threads is left open. Furthermore, the whole point of java is not having to worry about stuff like this. If you do, you're probably either using the wrong tool (try C++) or going about your problem the wrong way. There may be legitimate reasons to rely on this information in java, but I can't think of any. > Furthermore, the whole point of java is not having to worry about stuff > like this. If you do, you're probably either using the wrong tool (try > C++) or going about your problem the wrong way. There may be legitimate > reasons to rely on this information in java, but I can't think of any. It can be very relevant to know the implementation of Java threads on ones platform for both application, operating system and hardware configuration. Arne >>> When you write Thread t = new MyThread(); r.start(), do you get a new >>> thread (you know like in Linux you call pthread_create() and kernel [quoted text clipped - 11 lines] > C++) or going about your problem the wrong way. There may be legitimate > reasons to rely on this information in java, but I can't think of any. What about programs that need more than one second of CPU time per second of elapsed time? Multiple OS threads can run on different processors at the same time. A single OS thread can never get more than one processor. Patricia >>>> When you write Thread t = new MyThread(); r.start(), do you get a >>>> new thread (you know like in Linux you call pthread_create() and [quoted text clipped - 17 lines] > processors at the same time. A single OS thread can never get more > than one processor. Yes. If the OP's question were qualified to be asking about a specific Java implementation (including version), it could be answered in detail, and that detail might be of real importance. It's a fallacy to conclude from "Java can be used to write very portable applications" that "Java should *only* be used to write very portable applications." > Furthermore, the whole point of java is not having to worry about stuff > like this. If you do, you're probably either using the wrong tool (try > C++) or going about your problem the wrong way. There may be legitimate > reasons to rely on this information in java, but I can't think of any Unfortunately, that is almost completely untrue. In an ideal world it /would/ be true, but this is not that world... The design space which can be approached by "green" threads has only a small overlap with the design space which is suitable for OS-level threads -- unless the OS itself provides light-weight threads, and that is in general /not/ the case (there are exceptions). If you are only using a small number of threads, and do not care greatly about the amount of actual concurrency you achieve -- i.e you are using the threads only as a code structuring mechanism -- then it makes little difference how the threads are implemented. For all the other cases, you do have to care, and you may be forced to use /very/ different designs for your application depending on how threads are implemented. -- chris >> When you write Thread t = new MyThread(); r.start(), do you get a new >> thread (you know like in Linux you call pthread_create() and kernel [quoted text clipped - 5 lines] > lightweight threading package, or by having a single-threaded interpreter > round-robin among the active threads is left open. It would probably be impossible to define something like this in the Java standard, because Java runs on so many different platform. But I believe that recent Java versions for common platforms tend to map Java threads to native threads 1:1. Some Java implementations has a -X or -XX switch to specify the threading model to use. Arne >>> When you write Thread t = new MyThread(); r.start(), do you get a new >>> thread (you know like in Linux you call pthread_create() and kernel [quoted text clipped - 12 lines] > But I believe that recent Java versions for common platforms > tend to map Java threads to native threads 1:1. That's been true for Sun's JDK for Linux from at least version 1.3 - its easy to prove: start a Java app from one console window, switch to another, type "ps -u/username/" and look at all the processes[1] with the same name as the Java app. [1] Like most Unices, Linux uses the same mechanism to schedule and execute both threads and processes.  Signaturemartin@ | Martin Gregorie gregorie. | Essex, UK org | Sorry I see my question should be more specific about OS. So, for Operating System Microsoft Windows XP Professional Operating System Version 5.1.2600 (dual Intel(R) Pentium(R) 4 CPU 3.00GHz) JVM version 1.5.0_07 Can anyone please answre my question and what I should set for flags to java.exe or javac.exe so I get (if possible) one thread per call to Thread t= new Thread(); t.run() Thank you and also thanks for people who posted about this knowledge being useful. > Sorry I see my question should be more specific about OS. So, for > Operating System Microsoft Windows XP Professional [quoted text clipped - 6 lines] > java.exe or javac.exe so I get (if possible) one thread per call to > Thread t= new Thread(); t.run() SUN Java / Windows / x86 is 1 Java thread = 1 Windows thread Arne Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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