openjdk – California Sunshine

How to get the OpenJDK binary tar/zip file?

Since Oracle updated their license for Java 8, a lot of companies started officially maintaining OpenJDK, such as Redhat, Amazon, Alibaba and etc. It’s a good time to switch to OpenJDK.

Unlike Oracle, Redhat doesn’t provide the portable tar/zip of pre-built OpenJDK Linux edition. The zip files are only for Windows. Redhat recommends you to use the offical RPM package to install. Generally, it’s better solution but sometimes it’s very inconvenience, especially when you don’t have the permission but you want to have a quick deployment.

What to do? Docker could help!

Pull the image of the CentOS you need. In my case, I used a CentOS 7.7 image.

docker pull centos:centos7.7.1908

1	docker pull centos:centos7.7.1908

Start the container

docker run -i -t centos:centos7.7.108 /bin/bash

1	docker run -i -t centos:centos7.7.108 /bin/bash

Install the OpenJDK you need, such as OpenJDK8 or OpenJDK11. For example,

yum update
yum install java-1.8.0-openjdk

1 2	yum update yum install java-1.8.0-openjdk

Find where the JDK is. In my case, it’s /usr/lib/jvm/java-11-openjdk-11.0.5.10-0.el7_7.x86_64

ls /etc/alternative

1	ls /etc/alternative

Make a tar file of that folder
Copy this tar file out to your local.

By this way, you can get the compatible tar/zip file out. Usually, the dependencies should be fulfilled.

Build OpenJFX 8 in CentOS 6.7 Docker Container

OpenJDK 8 doesn’t include OpenJFX by default. And to make OpenJFX work on old Linux distribution, such as CentOS 6.7, you can not simply follow the official instructions. This article will talk about how to build OpenJFX 8 in CentOS 6.7 docker container.

Start docker container

With docker, it’s extremely easy to get CentOS 6.7 environment.

docker pull centos:6.7
docker run -it centos:6.7

1 2	docker pull centos:6.7 docker run -it centos:6.7

Instructions

Yum Install Packages

yum install mercurial bison flex gperf ksh pkgconfig \
    libpng12-devel libjpeg-devel libxml2-devel \
    libxslt-devel systemd-devel glib2-devel  gtk2-devel \
    libXtst-devel pango-devel freetype-devel wget unzip vim java-1.8.0-openjdk-devel java-1.8.0-openjdk java-1.8.0-openjdk-headless \
    libXxf86vm-devel mesa-libGL-devel perl-Time-HiRes tar perl-JSON

yum install mercurial bison flex gperf ksh pkgconfig \

libpng12-devel libjpeg-devel libxml2-devel \

libxslt-devel systemd-devel glib2-devel gtk2-devel \

libXtst-devel pango-devel freetype-devel wget unzip vim java-1.8.0-openjdk-devel java-1.8.0-openjdk java-1.8.0-openjdk-headless \

libXxf86vm-devel mesa-libGL-devel perl-Time-HiRes tar perl-JSON

Install GCC/G++ 6, Python 2.7, Ruby 2.4

Reference is https://www.softwarecollections.org/en/scls/rhscl/devtoolset-6/.

yum install centos-release-scl
yum install devtoolset-6
yum install python27
yum install rh-ruby24
scl enable devtoolset-6 bash
scl enable python27 bash
scl enable rh-ruby24 bash

yum install centos-release-scl

yum install devtoolset-6

yum install python27

yum install rh-ruby24

scl enable devtoolset-6 bash

scl enable python27 bash

scl enable rh-ruby24 bash

Install Gradle, CMake, Ant

Install gradle 4.8 and ant 1.10, update $PATH.

root@host ~# wget https://services.gradle.org/distributions/gradle-4.8-bin.zip
root@host ~# unzip gradle-4.8-bin.zip
root@host ~# wget http://mirror.cogentco.com/pub/apache//ant/binaries/apache-ant-1.10.5-bin.zip
root@host ~# unzip apache-ant-1.10.5-bin.zip
root@host ~# wget https://github.com/Kitware/CMake/releases/download/v3.13.4/cmake-3.13.4.tar.gz
root@host ~# tar xf cmake-3.13.4.tar.gz
root@host ~# export PATH=/root/apache-ant-1.10.5/bin:/root/gradle-4.8/bin:/root/cmake-3.13.4-Linux-x86_64/bin:$PATH

root@host ~# wget https://services.gradle.org/distributions/gradle-4.8-bin.zip

root@host ~# unzip gradle-4.8-bin.zip

root@host ~# wget http://mirror.cogentco.com/pub/apache//ant/binaries/apache-ant-1.10.5-bin.zip

root@host ~# unzip apache-ant-1.10.5-bin.zip

root@host ~# wget https://github.com/Kitware/CMake/releases/download/v3.13.4/cmake-3.13.4.tar.gz

root@host ~# tar xf cmake-3.13.4.tar.gz

root@host ~# export PATH=/root/apache-ant-1.10.5/bin:/root/gradle-4.8/bin:/root/cmake-3.13.4-Linux-x86_64/bin:$PATH

Sync OpenJFX 8 source code

hg clone http://hg.openjdk.java.net/openjfx/8u-dev/rt

1	hg clone http://hg.openjdk.java.net/openjfx/8u-dev/rt

Build without Webkit

Skip the samples and scene-builder build – “vim rt/build.gradle” and comment on the following lines

def appsJar = project.task("appsJar${t.capital}") {
     dependsOn(sdk, getLucene)
     doLast() {
       ant.properties['targetBld'] = "$t.name"
       if (!rootProject.ext[t.upper].compileSwing) {
         ant.properties['JFX_CORE_ONLY'] = 'true'
       }
       ant.properties['jfxbuild.jfxrt.jar'] = jfxrtJar
       ant.properties['platforms.JDK_1.8.home'] = "${rootProject.ext.JDK_HOME}"

       // comment the following several lines
       // ant.project.executeTarget("sampleAppsJar")
       // ant.project.executeTarget("scenebuilderSampleAppsJar")

       // if (!t.name.startsWith("arm")) {
       //   ant.project.executeTarget("scenebuilderAppJar")
       // }
     }
 }
 rootProject.appsjar.dependsOn(appsJar)

 def appsClean = project.task("appsClean${t.capital}") {
     doLast() {
       ant.properties['targetBld'] = "$t.name"
       ant.properties['platforms.JDK_1.8.home'] = "${rootProject.ext.JDK_HOME}"

       // comment the following several lines
       // ant.project.executeTarget("sampleAppsClean")
       // ant.project.executeTarget("scenebuilderSampleAppsClean")
       // if (!t.name.startsWith("arm")) {
       //   ant.project.executeTarget("scenebuilderAppClean")
       // }
       // delete(ensembleLibDir);
     }
 }
 rootProject.clean.dependsOn(appsClean)

				
					
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						def appsJar = project.task("appsJar${t.capital}") {
     dependsOn(sdk, getLucene)
     doLast() {
       ant.properties['targetBld'] = "$t.name"
       if (!rootProject.ext[t.upper].compileSwing) {
         ant.properties['JFX_CORE_ONLY'] = 'true'
       }
       ant.properties['jfxbuild.jfxrt.jar'] = jfxrtJar
       ant.properties['platforms.JDK_1.8.home'] = "${rootProject.ext.JDK_HOME}"
 
       // comment the following several lines
       // ant.project.executeTarget("sampleAppsJar")
       // ant.project.executeTarget("scenebuilderSampleAppsJar")
 
       // if (!t.name.startsWith("arm")) {
       //   ant.project.executeTarget("scenebuilderAppJar")
       // }
     }
 }
 rootProject.appsjar.dependsOn(appsJar)
 
 def appsClean = project.task("appsClean${t.capital}") {
     doLast() {
       ant.properties['targetBld'] = "$t.name"
       ant.properties['platforms.JDK_1.8.home'] = "${rootProject.ext.JDK_HOME}"
 
       // comment the following several lines
       // ant.project.executeTarget("sampleAppsClean")
       // ant.project.executeTarget("scenebuilderSampleAppsClean")
       // if (!t.name.startsWith("arm")) {
       //   ant.project.executeTarget("scenebuilderAppClean")
       // }
       // delete(ensembleLibDir);
     }
 }
 rootProject.clean.dependsOn(appsClean)

					

			

Start Gradle build.

# go to the source folder and start the gradle build.
cd rt
gradle
gradle zips

# go to the source folder and start the gradle build.

cd rt

gradle

gradle zips

when the build is done, the javafx–sdk-overlay.zip will be generated.

[root@8b5e71c7c0e3 bundles]# readlink -f javafx-sdk-overlay.zip
/root/rt/build/bundles/javafx-sdk-overlay.zip

1 2	[root@8b5e71c7c0e3 bundles]# readlink -f javafx-sdk-overlay.zip /root/rt/build/bundles/javafx-sdk-overlay.zip

Build with Webkit

With WebKit, the compilation will become extremely slow.

Before doing the steps of “Build without Webkit”, do the following extra steps.

Copy the gradle.properties from the template and enable the Webkit compiling

cp gradle.properties.template gradle.properties

1	cp gradle.properties.template gradle.properties

Enable “COMPILE_WEBKIT“, “BUILD_JAVADOC“, “BUILD_SRC_ZIP“, And specify COMPILE_TARGETS as “linux”

COMPILE_WEBKIT = true
#COMPILE_MEDIA = true

#To disable building support for JRockit Flight Recorder, uncomment the line below

#COMPILE_JFR = false

# so dfs to speed up the time in incremental builds. Uncomment this flag in order to
# build all the JavaDoc

BUILD_JAVADOC = true

# The building of the javafx-src bundle takes time. By default we disable the
# building of javafx-src so as to speed up the time in incremental builds.
# Uncomment this flag in order to build javafx-src.zip

BUILD_SRC_ZIP = true

.....


COMPILE_TARGETS = linux

				
					
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						COMPILE_WEBKIT = true
#COMPILE_MEDIA = true
 
#To disable building support for JRockit Flight Recorder, uncomment the line below
 
#COMPILE_JFR = false
 
# so dfs to speed up the time in incremental builds. Uncomment this flag in order to
# build all the JavaDoc
 
BUILD_JAVADOC = true
 
# The building of the javafx-src bundle takes time. By default we disable the
# building of javafx-src so as to speed up the time in incremental builds.
# Uncomment this flag in order to build javafx-src.zip
 
BUILD_SRC_ZIP = true
 
.....
 
 
COMPILE_TARGETS = linux

					

			

Update buildSrc/linux.gradle a little bit.

...

// def compiler = IS_COMPILE_PARFAIT ? "parfait-gcc" : "${toolchainDir}gcc";
def compiler = IS_COMPILE_PARFAIT ? "parfait-gcc" : "/opt/rh/devtoolset-6/root/usr/bin/gcc";
// def linker = IS_COMPILE_PARFAIT ? "parfait-g++" : "${toolchainDir}g++";
def linker = IS_COMPILE_PARFAIT ? "parfait-g++" : "/opt/rh/devtoolset-6/root/usr/bin/g++";

...

...

// def compiler = IS_COMPILE_PARFAIT ? "parfait-gcc" : "${toolchainDir}gcc";

def compiler = IS_COMPILE_PARFAIT ? "parfait-gcc" : "/opt/rh/devtoolset-6/root/usr/bin/gcc";

// def linker = IS_COMPILE_PARFAIT ? "parfait-g++" : "${toolchainDir}g++";

def linker = IS_COMPILE_PARFAIT ? "parfait-g++" : "/opt/rh/devtoolset-6/root/usr/bin/g++";

...

Update the symbolic link of /usr/bin/python2

[root@8b5e71c7c0e3 rt]# rm /usr/bin/python2
rm: remove symbolic link `/usr/bin/python2'? y
[root@8b5e71c7c0e3 rt]# ln -s /opt/rh/python27/root/usr/bin/python /usr/bin/python2

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						[root@8b5e71c7c0e3 rt]# rm /usr/bin/python2
rm: remove symbolic link `/usr/bin/python2'? y
[root@8b5e71c7c0e3 rt]# ln -s /opt/rh/python27/root/usr/bin/python /usr/bin/python2

Do the steps of “Build without Webkit“.

聊聊ClassLoader in Java World

ClassLoader是Java技术中非常主要的概念，原因是它用来加载Java Class。如果没有Class，也就没有对象；没有对象，就没有之后的一切了。

Java ClassLoader的默认实现是一种双亲结构，即总是尝试让Parent ClassLoader加载类。这样有一些优点，当然也有很大的限制，比如就不利于不同Module对多版本类的加载。更多的细节，在下面我做的PPT里。

Let's talk about java class loader from Yongqiang Li

还有些新的理解和发现。

自定义的ClassLoader可以把Parent ClassLoader设置为null，如果再把loadClass函数重写，就可以完全屏蔽default classLoader的影响。如OSGi的Bundle ClassLoader的最终的Parent就不是Bootstrap ClassLoader（Bundle ClassLoader的实现还是会去从默认ClassLoader去加载java.*的类）。
程序执行时，ClassLoader的选择。做几个小实验你就会发现，默认的ClassLoader是“加载当前执行函数所在类的ClassLoader”。在OpenJDK的源码中一通Search，就可以找到一些端倪。

在源文件src\interp\engine\interp.c中，有executeJava()函数中，执行ByteCode之前，先准备了MethodBlock的指针，它中间

uintptr_t *executeJava() {
    ...

    uintptr_t *arg1;
    register CodePntr pc;
    ExecEnv *ee = getExecEnv();
    Frame *frame = ee-&gt;last_frame;
    register uintptr_t *lvars = frame-&gt;lvars;
    register uintptr_t *ostack = frame-&gt;ostack;

    Object *this = (Object*)lvars[0];
    <strong>MethodBlock *new_mb, *mb = frame-&gt;mb;</strong>
    ConstantPool *cp = &amp;(CLASS_CB(mb-&gt;class)-&gt;constant_pool);

uintptr_t *executeJava() {

...

uintptr_t *arg1;

ExecEnv *ee = getExecEnv();

Frame *frame = ee->last_frame;

Object *this = (Object*)lvars[0];

MethodBlock *new_mb, *mb = frame->mb;

ConstantPool *cp = &(CLASS_CB(mb->class)->constant_pool);

可以看看GETSTATIC这个指令的实现（此指令会在读取类的静态方法时调用）。可以看到resolveField()方法，并在mb的Class指针传入。idx是Static Field对应Constant Pool里的index。

... 

DEF_OPC_RW(OPC_GETSTATIC, ({
        int idx, cache, opcode;
        FieldBlock *fb;
        Operand operand;
               
        WITH_OPCODE_CHANGE_CP_DINDEX(OPC_GETSTATIC, idx, cache);

        frame-&gt;last_pc = pc;
        <strong>fb = resolveField(mb-&gt;class, idx);</strong>

        if(fb != NULL)
            initClass(fb-&gt;class);

        if(exceptionOccurred0(ee))
            goto throwException;

        if((*fb-&gt;type == 'J') || (*fb-&gt;type == 'D'))
            opcode = OPC_GETSTATIC2_QUICK;
        else
            if(*fb-&gt;type == 'L' || *fb-&gt;type == '[')
                opcode = OPC_GETSTATIC_QUICK_REF;
            else
                opcode = OPC_GETSTATIC_QUICK;

        operand.pntr = fb;
        OPCODE_REWRITE(opcode, cache, operand);

        REDISPATCH
    });)

...

...

DEF_OPC_RW(OPC_GETSTATIC, ({

int idx, cache, opcode;

FieldBlock *fb;

Operand operand;

WITH_OPCODE_CHANGE_CP_DINDEX(OPC_GETSTATIC, idx, cache);

frame->last_pc = pc;

fb = resolveField(mb->class, idx);

if(fb != NULL)

initClass(fb->class);

if(exceptionOccurred0(ee))

goto throwException;

if((*fb->type == 'J') || (*fb->type == 'D'))

opcode = OPC_GETSTATIC2_QUICK;

else

if(*fb->type == 'L' || *fb->type == '[')

opcode = OPC_GETSTATIC_QUICK_REF;

else

opcode = OPC_GETSTATIC_QUICK;

operand.pntr = fb;

OPCODE_REWRITE(opcode, cache, operand);

REDISPATCH

});)

...

resolveField中被调用resolveClass函数

FieldBlock *resolveField(Class *class, int cp_index) {
    ConstantPool *cp = &amp;(CLASS_CB(class)-&gt;constant_pool);
    FieldBlock *fb = NULL;

retry:
    switch(CP_TYPE(cp, cp_index)) {
        ...
        
        case CONSTANT_Fieldref: {
            Class *resolved_class;
            char *fieldname, *fieldtype;
            int cl_idx = CP_FIELD_CLASS(cp, cp_index);
            int name_type_idx = CP_FIELD_NAME_TYPE(cp, cp_index);

            MBARRIER();
            if(CP_TYPE(cp, cp_index) != CONSTANT_Fieldref)
                goto retry;

            fieldname = CP_UTF8(cp, CP_NAME_TYPE_NAME(cp, name_type_idx));
            fieldtype = CP_UTF8(cp, CP_NAME_TYPE_TYPE(cp, name_type_idx));
            <strong>resolved_class = resolveClass(class, cl_idx, TRUE, FALSE);</strong>

            ...

            break;
        }
    }
 
    return fb;
}

FieldBlock *resolveField(Class *class, int cp_index) {

ConstantPool *cp = &(CLASS_CB(class)->constant_pool);

FieldBlock *fb = NULL;

retry:

switch(CP_TYPE(cp, cp_index)) {

...

case CONSTANT_Fieldref: {

Class *resolved_class;

char *fieldname, *fieldtype;

int cl_idx = CP_FIELD_CLASS(cp, cp_index);

int name_type_idx = CP_FIELD_NAME_TYPE(cp, cp_index);

MBARRIER();

if(CP_TYPE(cp, cp_index) != CONSTANT_Fieldref)

goto retry;

fieldname = CP_UTF8(cp, CP_NAME_TYPE_NAME(cp, name_type_idx));

fieldtype = CP_UTF8(cp, CP_NAME_TYPE_TYPE(cp, name_type_idx));

resolved_class = resolveClass(class, cl_idx, TRUE, FALSE);

...

break;

}

return fb;

}

resolveClass又回调用findClassFromClass（其实是个Macro），同样传入class指针。看看Macro的定义，就可以很清楚了。

#define findClassFromClass(classname, class)                               \
    (CLASS_CB(class)->name == classname ? class :                          \
        findClassFromClassLoader(classname, CLASS_CB(class)->class_loader))

#define findClassFromClass(classname, class) \

(CLASS_CB(class)->name == classname ? class : \

findClassFromClassLoader(classname, CLASS_CB(class)->class_loader))

是从ClassBlock结构中找到对应的ClassLoader.

其实记住这个结论就好。这样就可以完全打错传统的ClassLoader的限制，比如OSGi Plugin/Bundle里的所有类就是由OSGi自己的加载器加载的，非常灵活，可以实现非常牛逼的功能！