《jdk8u源码分析》7.SetJvmEnvironment

src/share/bin/java.c::SetJvmEnvironment

/*
 * static void SetJvmEnvironment(int argc, char **argv);
 *   Is called just before the JVM is loaded.  We can set env variables
 *   that are consumed by the JVM.  This function is non-destructive,
 *   leaving the arg list intact.  The first use is for the JVM flag
 *   -XX:NativeMemoryTracking=value.
 */
static void
SetJvmEnvironment(int argc, char **argv) {

    static const char*  NMT_Env_Name    = "NMT_LEVEL_";

    int i;
    for (i = 0; i < argc; i++) {
        /*
         * The following case checks for "-XX:NativeMemoryTracking=value".
         * If value is non null, an environmental variable set to this value
         * will be created to be used by the JVM.
         * The argument is passed to the JVM, which will check validity.
         * The JVM is responsible for removing the env variable.
         */
        char *arg = argv[i];
        //判断命令行参数是否包含：-XX:NativeMemoryTracking=
        //如果是，根据值设置环境变量：NMT_LEVEL_${PID}=value，用以内存跟踪
        if (JLI_StrCCmp(arg, "-XX:NativeMemoryTracking=") == 0) {
            int retval;
            // get what follows this parameter, include "="
            size_t pnlen = JLI_StrLen("-XX:NativeMemoryTracking=");
            if (JLI_StrLen(arg) > pnlen) {
            	//获取参数值
                char* value = arg + pnlen;
                size_t pbuflen = pnlen + JLI_StrLen(value) + 10; // 10 max pid digits

                /*
                 * ensures that malloc successful
                 * DONT JLI_MemFree() pbuf.  JLI_PutEnv() uses system call
                 *   that could store the address.
                 */
                char * pbuf = (char*)JLI_MemAlloc(pbuflen);
				
				//拼接环境变量到pbuf中
                JLI_Snprintf(pbuf, pbuflen, "%s%d=%s", NMT_Env_Name, JLI_GetPid(), value);
                //设置环境变量，成功返回0，发生错误返回-1
                retval = JLI_PutEnv(pbuf);
                if (JLI_IsTraceLauncher()) {
                    char* envName;
                    char* envBuf;

                    // ensures that malloc successful
                    envName = (char*)JLI_MemAlloc(pbuflen);
                    JLI_Snprintf(envName, pbuflen, "%s%d", NMT_Env_Name, JLI_GetPid());

					//TRACER_MARKER: NativeMemoryTracking: env var is NMT_LEVEL_11380
                    printf("TRACER_MARKER: NativeMemoryTracking: env var is %s\n",envName);
					//TRACER_MARKER: NativeMemoryTracking: putenv arg NMT_LEVEL_11380=summary
                    printf("TRACER_MARKER: NativeMemoryTracking: putenv arg %s\n",pbuf);
                    envBuf = getenv(envName);
                    //TRACER_MARKER: NativeMemoryTracking: got value summary
                    printf("TRACER_MARKER: NativeMemoryTracking: got value %s\n",envBuf);
                    free(envName);
                }

            }

        }

    }
}