Java 外部函数接口：JNI, JNA, JNR http://nullwy.me/2018/01/java-ffi/

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Java 本地方法调用实现调用 getpid 对比，JNI vs. JNA vs. JNR

JNI 示例编译与运行（Mac 环境）：

$ mkdir -p target/classes
$ javac src/main/java/com/test/GetPidJni.java -d "target/classes"
$ javah -cp "target/classes" com.test.GetPidJni
$ gcc -I $JAVA_HOME/include -I $JAVA_HOME/include/darwin -dynamiclib -o libgetpidjni.dylib com_test_GetPidJni.c
$ java -Djava.library.path=`pwd` -cp "target/classes" com.test.GetPidJni

JNA 示例编译与运行（包括 Interface Mapping 和 Direct Mapping 两种方式）：

$ mvn install
$ java -cp "target/java-ffi-1.0-SNAPSHOT-jar-with-dependencies.jar" com.test.GetPidJna
$ java -cp "target/java-ffi-1.0-SNAPSHOT-jar-with-dependencies.jar" com.test.GetPidJnaDirect

JNR 示例编译与运行：

$ mvn install
$ java -cp "target/java-ffi-1.0-SNAPSHOT-jar-with-dependencies.jar" com.test.GetPidJnr

JMH 性能测试代码：

$ mvn install
$ java -cp "target/java-ffi-1.0-SNAPSHOT-jar-with-dependencies.jar" com.test.BenchmarkFFI

JMH 性能测试结果：

# JMH version: 1.19
# VM version: JDK 1.8.0_144, VM 25.144-b01
Benchmark                          Mode  Cnt      Score      Error   Units
BenchmarkFFI.testGetPidJna        thrpt   10   8225.209 ±  206.829  ops/ms
BenchmarkFFI.testGetPidJnaDirect  thrpt   10  10257.505 ±  736.135  ops/ms
BenchmarkFFI.testGetPidJni        thrpt   10  77852.899 ± 3167.101  ops/ms
BenchmarkFFI.testGetPidJnr        thrpt   10  58261.657 ± 5187.550  ops/ms

即：JNI > JNR > JNA (Direct Mapping) > JNA (Interface Mapping)

参见资料：

2013-07 Charles Nutter: Java Native Runtime http://www.oracle.com/technetwork/java/jvmls2013nutter-2013526.pdf