8359706: Add file descriptor count to VM.info

Reviewed-by: kevinw, stuefe

src/hotspot/os/aix/os_aix.cpp

@@ -2667,3 +2667,7 @@ void os::print_memory_mappings(char* addr, size_t bytes, outputStream* st) {}
 void os::jfr_report_memory_info() {}
 
 #endif // INCLUDE_JFR
+
+void os::print_open_file_descriptors(outputStream* st) {
+  // File descriptor counting not implemented on AIX
+}

src/hotspot/os/bsd/os_bsd.cpp

@@ -76,6 +76,7 @@
 # include <fcntl.h>
 # include <fenv.h>
 # include <inttypes.h>
+# include <mach/mach.h>
 # include <poll.h>
 # include <pthread.h>
 # include <pwd.h>
@@ -102,6 +103,7 @@
 #endif
 
 #ifdef __APPLE__
+  #include <libproc.h>
   #include <mach/task_info.h>
   #include <mach-o/dyld.h>
 #endif
@@ -2596,3 +2598,45 @@ bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {
 
   return res;
 } // end: os::pd_dll_unload()
+
+void os::print_open_file_descriptors(outputStream* st) {
+#ifdef __APPLE__
+  char buf[1024 * sizeof(struct proc_fdinfo)];
+  os::Bsd::print_open_file_descriptors(st, buf, sizeof(buf));
+#else
+  st->print_cr("Open File Descriptors: unknown");
+#endif
+}
+
+void os::Bsd::print_open_file_descriptors(outputStream* st, char* buf, size_t buflen) {
+#ifdef __APPLE__
+  pid_t my_pid;
+
+  // ensure the scratch buffer is big enough for at least one FD info struct
+  assert(buflen >= sizeof(struct proc_fdinfo));
+  kern_return_t kres = pid_for_task(mach_task_self(), &my_pid);
+  if (kres != KERN_SUCCESS) {
+    st->print_cr("Open File Descriptors: unknown");
+    return;
+  }
+  size_t max_fds = buflen / sizeof(struct proc_fdinfo);
+  struct proc_fdinfo* fds = reinterpret_cast<struct proc_fdinfo*>(buf);
+
+  // fill our buffer with FD info, up to the available buffer size
+  int res = proc_pidinfo(my_pid, PROC_PIDLISTFDS, 0, fds, max_fds * sizeof(struct proc_fdinfo));
+  if (res <= 0) {
+    st->print_cr("Open File Descriptors: unknown");
+    return;
+  }
+
+  // print lower threshold if count exceeds buffer size
+  int nfiles = res / sizeof(struct proc_fdinfo);
+  if ((size_t)nfiles >= max_fds) {
+    st->print_cr("Open File Descriptors: > %zu", max_fds);
+    return;
+  }
+  st->print_cr("Open File Descriptors: %d", nfiles);
+#else
+  st->print_cr("Open File Descriptors: unknown");
+#endif
+}

src/hotspot/os/bsd/os_bsd.hpp

@@ -123,6 +123,8 @@ class os::Bsd {
   static int get_node_by_cpu(int cpu_id);
 
   static void print_uptime_info(outputStream* st);
+  static void print_open_file_descriptors(outputStream* st, char* buf, size_t buflen);
+  static void print_open_file_descriptors(outputStream* st);
 };
 
 #endif // OS_BSD_OS_BSD_HPP

src/hotspot/os/linux/os_linux.cpp

@@ -83,6 +83,7 @@
 #endif
 
 # include <ctype.h>
+# include <dirent.h>
 # include <dlfcn.h>
 # include <endian.h>
 # include <errno.h>
@@ -113,6 +114,7 @@
 # include <sys/types.h>
 # include <sys/utsname.h>
 # include <syscall.h>
+# include <time.h>
 # include <unistd.h>
 #ifdef __GLIBC__
 # include <malloc.h>
@@ -2161,6 +2163,8 @@ void os::print_os_info(outputStream* st) {
 
   os::Posix::print_rlimit_info(st);
 
+  os::print_open_file_descriptors(st);
+
   os::Posix::print_load_average(st);
   st->cr();
 
@@ -5429,3 +5433,33 @@ bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {
 
   return res;
 } // end: os::pd_dll_unload()
+
+void os::print_open_file_descriptors(outputStream* st) {
+  DIR* dirp = opendir("/proc/self/fd");
+  int fds = 0;
+  struct dirent* dentp;
+  const jlong TIMEOUT_NS = 50000000L;  // 50 ms in nanoseconds
+  bool timed_out = false;
+
+  // limit proc file read to 50ms
+  jlong start = os::javaTimeNanos();
+  assert(dirp != nullptr, "No proc fs?");
+  while ((dentp = readdir(dirp)) != nullptr && !timed_out) {
+    if (isdigit(dentp->d_name[0])) fds++;
+    if (fds % 100 == 0) {
+      jlong now = os::javaTimeNanos();
+      if ((now - start) > TIMEOUT_NS) {
+        timed_out = true;
+      }
+    }
+  }
+
+  closedir(dirp);
+  if (timed_out) {
+    st->print_cr("Open File Descriptors: > %d", fds);
+  } else {
+    st->print_cr("Open File Descriptors: %d", fds);
+  }
+}
+
+

src/hotspot/os/windows/os_windows.cpp

@@ -6276,6 +6276,10 @@ const void* os::get_saved_assert_context(const void** sigInfo) {
   return nullptr;
 }
 
+void os::print_open_file_descriptors(outputStream* st) {
+  // File descriptor counting not supported on Windows.
+}
+
 /*
  * Windows/x64 does not use stack frames the way expected by Java:
  * [1] in most cases, there is no frame pointer. All locals are addressed via RSP

src/hotspot/share/runtime/os.hpp

@@ -893,6 +893,9 @@ class os: AllStatic {
   static void print_date_and_time(outputStream* st, char* buf, size_t buflen);
   static void print_elapsed_time(outputStream* st, double time);
 
+  // Prints the number of open file descriptors for the current process
+  static void print_open_file_descriptors(outputStream* st);
+
   static void print_user_info(outputStream* st);
   static void print_active_locale(outputStream* st);
 

src/hotspot/share/utilities/vmError.cpp

@@ -1329,6 +1329,13 @@ void VMError::report(outputStream* st, bool _verbose) {
   STEP_IF("printing OS information", _verbose)
     os::print_os_info(st);
     st->cr();
+#ifdef __APPLE__
+    // Avoid large stack allocation on Mac for FD count during signal-handling.
+    os::Bsd::print_open_file_descriptors(st, buf, sizeof(buf));
+    st->cr();
+#else
+    os::print_open_file_descriptors(st);
+#endif
 
   STEP_IF("printing CPU info", _verbose)
     os::print_cpu_info(st, buf, sizeof(buf));
@@ -1550,6 +1557,8 @@ void VMError::print_vm_info(outputStream* st) {
 
   os::print_os_info(st);
   st->cr();
+  os::print_open_file_descriptors(st);
+  st->cr();
 
   // STEP("printing CPU info")
 

test/jdk/sun/tools/jcmd/TestJcmdSanity.java

@@ -33,7 +33,6 @@ import java.util.List;
 import jdk.test.lib.process.OutputAnalyzer;
 import jdk.test.lib.process.ProcessTools;
 import jdk.test.lib.Platform;
-import jdk.test.lib.Utils;
 
 /*
  * @test
@@ -182,5 +181,10 @@ public class TestJcmdSanity {
           output.shouldNotContain("*** Handler was modified!");
           output.shouldNotContain("*** Expected: "); // e.g. *** Expected: javaSignalHandler in ...
         }
+
+        // Should find file descriptor counting on Mac and Linux
+        if (Platform.isLinux() || Platform.isOSX()) {
+            output.shouldMatch("Open File Descriptors: \\d+");
+        }
     }
 }