SapMachine #1593: Implement a lean alternative for jcmd

make/modules/java.base/Launcher.gmk

@@ -87,4 +87,17 @@ ifeq ($(call isTargetOs, macosx aix linux), true)
   TARGETS += $(BUILD_JSPAWNHELPER)
 endif
 
+# SapMachine 2024-01-24: Build a lean version of jcmd on Linux
+ifeq ($(call isTargetOs, macosx linux), true)
+  $(eval $(call SetupJdkExecutable, BUILD_LEANJCMD, \
+      NAME := leanjcmd, \
+      SRC := $(TOPDIR)/src/$(MODULE)/unix/native/leanjcmd, \
+      OPTIMIZATION := LOW, \
+      CFLAGS := $(CFLAGS_JDKEXE) -I$(TOPDIR)/src/$(MODULE)/unix/native/libjava, \
+      LDFLAGS := $(LDFLAGS_JDKEXE), \
+  ))
+
+  TARGETS += $(BUILD_LEANJCMD)
+endif
+
 ################################################################################

src/java.base/unix/native/leanjcmd/leanjcmd.c

@@ -0,0 +1,215 @@
+/*
+ * Copyright (c) 2024 SAP SE. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/un.h>
+
+static int attach_file_fd = -1;
+static char attach_path[256];
+
+static void cleanup() {
+  if (attach_file_fd >= 0) {
+    unlink(attach_path);
+  }
+}
+
+static int file_exists(char const* path) {
+  struct stat stat_buf;
+
+  return stat(path, &stat_buf) == 0;
+}
+
+static void fail(char const* msg) {
+  if (msg) {
+    fprintf(stderr, "%s", msg);
+  }
+
+  exit(1);
+}
+
+static void fail_with_errno(char const* msg) {
+  perror(msg);
+  fail(NULL);
+}
+
+static void write_full(int fd, char const* buf, int size) {
+  ssize_t written;
+
+  while ((written = write(fd, buf, size)) != size) {
+    if (written <= 0) {
+      fail_with_errno("Could not write");
+    }
+
+    buf += written;
+    size -= written;
+  }
+}
+
+static void write_tag(int fd, char const* str) {
+  write_full(fd, str, strlen(str) + 1);
+}
+
+static void write_string(int fd, char const* str) {
+  write_full(fd, str, strlen(str));
+}
+
+static void run_jcmd(pid_t pid, int argc, char *argv[]) {
+  char pid_file[256];
+  sprintf(pid_file, "/tmp/.java_pid%d", (int) pid);
+
+  if (!file_exists(pid_file)) {
+    return;
+  }
+
+  int fd = socket(PF_UNIX, SOCK_STREAM, 0);
+
+  if (fd < 0) {
+    fail_with_errno("Could not create file socket");
+  }
+
+  struct sockaddr_un addr;
+  memset(&addr, 0, sizeof(addr));
+  addr.sun_family = AF_UNIX;
+  strncpy(addr.sun_path, pid_file, sizeof(addr.sun_path) - 1);
+
+  if (connect(fd, (struct sockaddr*) &addr, sizeof(addr)) != 0) {
+    fail_with_errno("Could not connect to file socket");
+  }
+
+  write_tag(fd, "1");
+  write_tag(fd, "jcmd");
+
+  if (argc == 0) {
+    write_tag(fd, "help");
+  } else {
+    for (int i = 0; i < argc; ++i) {
+      if (i > 0) {
+        write_string(fd, " ");
+      }
+
+      write_string(fd, argv[i]);
+    }
+
+    write_tag(fd, "");
+  }
+
+  write_tag(fd, "");
+  write_tag(fd, "");
+
+  char buf[256];
+  int c = read(fd, buf, sizeof(buf));
+
+  if (c <= 0) {
+    fail("Missing result code\n");
+  }
+
+  int result_code;
+
+  if (sscanf(buf, "%d", &result_code) != 1) {
+    fail("Invalid result code\n");
+  }
+
+  printf("%d:\n", pid);
+  fflush(stdout);
+
+  for (int i = 0; i < c; ++i) {
+    if (buf[i] == '\n') {
+      write_full(1, buf + i + 1, c - i - 1);
+      break;
+    }
+  }
+
+  while ((c = read(fd, buf, sizeof(buf))) > 0) {
+    write_full(1, buf, c);
+  }
+
+  exit(result_code == 0 ? 0 : 1);
+}
+
+static void trigger_attach(int pid) {
+  snprintf(attach_path, sizeof(attach_path), "/tmp/.attach_pid%d", pid);
+
+  // Create .attach_pid file if not already present.
+  if (!file_exists(attach_path)) {
+    attach_file_fd = creat(attach_path, S_IRWXU);
+
+    if (attach_file_fd < 0) {
+      fail_with_errno("Could not create .attach_pid file");
+    }
+
+    atexit(cleanup);
+  }
+
+  if (kill(pid, SIGQUIT) != 0) {
+    fail_with_errno("Could not signal pid");
+  }
+}
+
+int main(int argc, char *argv[]) {
+  if ((argc < 2) || (strcmp("-help", argv[1]) == 0)) {
+    printf("%s", "leanjcmd works like jcmd, but only supports attaching to a pid.\n");
+    printf("%s", "Usage: leanjcmd -help | <pid> [<command> ...]\n");
+    exit(0);
+  }
+
+  char* endptr;
+  long raw_pid = strtol(argv[1], &endptr, 10);
+
+  if ((argv[1][0] == '\0') || (endptr[0] != '\0')) {
+    fail("Could not parse pid.\n");
+  }
+
+  pid_t pid = (pid_t) raw_pid;
+
+  if ((raw_pid <= 0) || (raw_pid == LONG_MAX) || (raw_pid != pid)) {
+    fail("Pid is not in valid range.\n");
+  }
+
+  run_jcmd(pid, argc - 2, argv + 2);
+
+  // If attaching failed, trigger it and try again.
+  trigger_attach(pid);
+
+  for (int i = 0; i < 10; ++i) {
+    usleep(10000 * (1 << i));
+    run_jcmd(pid, argc - 2, argv + 2);
+  }
+
+  fail("Connection to VM timed out.\n");
+
+  return 0;
+}
+