What is the difference between -Xss and -XX:ThreadStackSize?
Solution 1
-Xss
is standard options recognized by the Java HotSpot VM.
-XX:ThreadStackSize
as other -XX
options are not stable and are subject to change without notice.
Solution 2
-Xss
is an alias for -XX:ThreadStackSize
both for OpenJDK and Oracle JDK.
Though they parse arguments differently:
-Xss
may accept a number with K, M or G suffix;
-XX:ThreadStackSize=
expects an integer (without suffix) - the stack size in kilobytes.
Solution 3
UPDATED 2019 for Java SE 8
Current Oracle Java SE 8 docs suggest that -Xss
and -XX:ThreadStackSize=size
are equivalent. See
https://docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html
For -Xss
:
-Xsssize
Sets the thread stack size (in bytes). Append the
letter k or K to indicate KB, m or M to indicate MB, g or G to
indicate GB. The default value depends on the platform:
Linux/ARM (32-bit): 320 KB
Linux/i386 (32-bit): 320 KB
Linux/x64 (64-bit): 1024 KB
OS X (64-bit): 1024 KB
Oracle Solaris/i386 (32-bit): 320 KB
Oracle Solaris/x64 (64-bit): 1024 KB
The following examples set the thread stack size to 1024 KB in different units:
-Xss1m
-Xss1024k
-Xss1048576
This option is equivalent to -XX:ThreadStackSize.
For -XX:ThreadStackSize=size
-XX:ThreadStackSize=size
Sets the thread stack size (in bytes). Append the
letter k or K to indicate kilobytes, m or M to indicate
megabytes, g or G to indicate gigabytes. The default
value depends on the platform:
Linux/ARM (32-bit): 320 KB
Linux/i386 (32-bit): 320 KB
Linux/x64 (64-bit): 1024 KB
OS X (64-bit): 1024 KB
Oracle Solaris/i386 (32-bit): 320 KB
Oracle Solaris/x64 (64-bit): 1024 KB
The following examples show how to set the thread stack size to 1024 KB in different units:
-XX:ThreadStackSize=1m
-XX:ThreadStackSize=1024k
-XX:ThreadStackSize=1048576
This option is equivalent to -Xss.
Solution 4
-Xss
works only on main
Java thead, but -XX:ThreadStackSize
works on all Java thread.
If -Xss (or -ss) were passed on the command line, it gets picked up directly by the launcher and is used later to create the "main" Java thread, without asking the VM for the preferred thread stack size. That where inconsistency comes from: if -Xss is given after -XX:ThreadStackSize, then things are still good; otherwise, the "main" Java thread would have a stack size specified by -Xss where as other Java threads' stack size would still follow that of ThreadStackSize.
Inconsistency between -Xss and -XX:ThreadStackSize in the java launcher
Solution 5
The Oracle Java SE 8 docs suggest that -Xss and -XX:ThreadStackSize=size are equivalent. However this not correct. Try eg.
java -XX:ThreadStackSize=1024 -version
java version "1.8.0_171"
Java(TM) SE Runtime Environment (build 1.8.0_171-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.171-b11, mixed mode)
java -Xss1024 -version
The stack size specified is too small, Specify at least 160k
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.
This is fixed e.g. in the Java 14 documentation:
-XX:ThreadStackSize=size Sets the Java thread stack size (in kilobytes). Use of a scaling suffix, such as k, results in the scaling of the kilobytes value so that -XX:ThreadStackSize=1k sets the Java thread stack size to 1024*1024 bytes or 1 megabyte.
and
-Xss size Sets the thread stack size (in bytes).
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user2078148
Updated on October 15, 2022Comments
-
user2078148 over 1 year
I just want to control the stack size for all of my threads in a Java (groovy) application. For the Hotspot Oracle VM, I know that there are two parameters doing that (
-Xss
andXX:ThreadStackSize
).Which is the preferred one? Is there any difference between them? Regarding Open JDK 7 someone asked on the mailing list, stating that
-Xss
is the same for the Hotpot VM as-XX:ThreadStackSize
.The point is, that I am measuring how many threads can be started on my system. My groovy script which does this looks like:
int count = 0 def printCountThreads = { println("XXX There were started $count threads.") } try { while(true){ new Thread({Thread.sleep(Integer.MAX_VALUE)}).start() count++ if(count % 1000 == 0){ printCountThreads() } } } catch (Throwable e){ printCountThreads() throw e }
Interestingly enough I just get a reduced number of of threads using -
XX:ThreadStackSize
. I am starting the groovy application with and with different content in the environment variable JAVA_OPTS.groovy countmax-threads.groovy
When I set JAVA_OPTS to
-XX:ThreadStackSize=2m
, I get about 1000 started threads until the memory is consumed. But, when I useJAVA_OPTS='-Xss2m'
, I get about 32000 threads until the expected error arises. So it seems that-Xss
does not work at all.I am using
java version "1.8.0_05"
Java(TM) SE Runtime Environment (build 1.8.0_05-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.5-b02, mixed mode)on a Ubuntu 14.04 64 bit machine with four hardware threads and about 8 GB of RAM.
UPDATE:
I reverified this on my Windows 7 64 bit machine and another JDK:
java version "1.8.0_20" Java(TM) SE Runtime Environment (build 1.8.0_20-b26) Java HotSpot(TM) 64-Bit Server VM (build 25.20-b23, mixed mode)
and there
-Xss
and-XX:ThreadStackSize
work as expected (as some answers pointed out). So I suppose it is a Linux specific problem or even a bug in the JDK version 1.8.05. -
user2078148 about 9 yearsThan why there behaviour differs?
-
alain.janinm about 9 years@user2078148 Dis you download the java hotspot from Oracle? The link where it's stated that -Xss and -XX:ThreadStackSize are equivalent is about openjdk. Openjdk and Oracle Hotspot VM might differ. See stackoverflow.com/a/11580321/1140748. So -XX:ThreadStackSize that might fail because -XX options are not stable.
-
user2078148 about 9 yearsThank you for your suggestion... but why than -XX:ThreadStackSize=2m just works and -Xss does not?
-
user2078148 about 9 yearsWell I don't encountered any problems in specifing -XX:ThreadStackSize=2m, altrough you are right, the docs say what you told me ... but this all makes it not clear
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user2078148 about 9 yearsThe cited mailing list post seems to apply for JDK 6 and 7. For JDK 8, I will verify that on my local machine again. You hint was really useful, thank you!
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user2078148 about 9 yearsWell after studying the mailing list post by Kris Mok in detail, I have to correct you. -Xss will work for the thread stack size as -XX:ThreadStackSize too. The problem arises when you are using both at the same time (in the order -Xss -XX:ThreadStackSize). In this case, the vm will pick up the value specified in -Xss only for the main thread and the value specified in -XXThreadStackSize for all other user threads. Those two options should be equivalent! One has to be careful when using both (which usually does not make any sense)
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Alan Thompson over 5 yearsOracle Java SE 8 docs suggest they are exact synonyms: docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html
-
Alan Thompson over 5 yearsOracle Java SE 8 docs suggest they are exact synonyms: docs.oracle.com/javase/8/docs/technotes/tools/unix/java.html
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alain.janinm over 5 yearsHi @AlanThompson, yes this might be possible, but it can change. If you can use an option not starting with -XX, then do it. -XX options are not stable and are subject to change without notice.
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Raj over 4 yearsThanks. When I provided "-Xss3m" as JAVA_OPTS but the GC logs printed "-XX:ThreadStackSize=3072". 3072 does not have any prefix and I was looking for confirmation that size is in kilobytes.