8359706: Add file descriptor count and maximum limit to VM.info

src/hotspot/os/aix/os_aix.cpp

@@ -79,6 +79,8 @@
 
 // put OS-includes here (sorted alphabetically)
 #include <alloca.h>
+#include <ctype.h>
+#include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <inttypes.h>
@@ -2717,3 +2719,22 @@ 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) {
+  char fd_dir[32];
+  snprintf(fd_dir, sizeof(fd_dir), "/proc/%d/fd", getpid());
+  DIR* dirp = opendir(fd_dir);
+  int fds = 0;
+  if (dirp != nullptr) {
+    struct dirent* dentp;
+    while ((dentp = readdir(dirp)) != nullptr) {
+      if (isdigit(dentp->d_name[0])) {
+        fds++;
+      }
+    }
+    closedir(dirp);
+    st->print_cr("OpenFileDescriptorCount = %d", fds - 1); // minus the opendir fd itself
+  } else {
+    st->print_cr("OpenFileDescriptorCount = unknown");
+  }
+}

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
@@ -2501,3 +2503,42 @@ bool os::pd_dll_unload(void* libhandle, char* ebuf, int ebuflen) {
 
   return res;
 } // end: os::pd_dll_unload()
+
+#ifdef __APPLE__
+void os::print_open_file_descriptors(outputStream* st) {
+  const int MAX_SAFE_FDS = 1024;
+  struct proc_fdinfo fds[MAX_SAFE_FDS];
+  struct proc_bsdinfo bsdinfo;
+  int nfiles;
+  kern_return_t kres;
+  int res;
+  size_t fds_size;
+  pid_t my_pid;
+
+  kres = pid_for_task(mach_task_self(), &my_pid);
+  if (kres != KERN_SUCCESS) {
+    st->print_cr("OpenFileDescriptorCount = unknown");
+    return;
+  }
+
+  res = proc_pidinfo(my_pid, PROC_PIDLISTFDS, 0, fds, MAX_SAFE_FDS * sizeof(struct proc_fdinfo));
+  if (res <= 0) {
+    st->print_cr("OpenFileDescriptorCount = unknown");
+    return;
+  }
+
+  nfiles = res / sizeof(struct proc_fdinfo);
+  if (nfiles >= MAX_SAFE_FDS) {
+    st->print_cr("OpenFileDescriptorCount = unknown");
+    return;
+  }
+
+  st->print_cr("OpenFileDescriptorCount = %d", nfiles);
+}
+#endif // __APPLE__
+
+#if defined(_ALLBSD_SOURCE) && !defined(__APPLE__)
+long os::get_open_file_descriptor_count() {
+    st->print_cr("OpenFileDescriptorCount = unknown");
+}
+#endif

src/hotspot/os/linux/os_linux.cpp

@@ -5449,3 +5449,20 @@ 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;
+  if (dirp != nullptr) {
+    struct dirent* dentp;
+    while ((dentp = readdir(dirp)) != nullptr) {
+      if (isdigit(dentp->d_name[0])) {
+        fds++;
+      }
+    }
+    closedir(dirp);
+    st->print_cr("OpenFileDescriptorCount = %d", fds - 1);
+  } else {
+    st->print_cr("OpenFileDescriptorCount = unknown");
+  }
+}

src/hotspot/os/windows/os_windows.cpp

@@ -6260,6 +6260,10 @@ 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

@@ -842,6 +842,9 @@ 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

@@ -1432,6 +1432,12 @@ void VMError::print_vm_info(outputStream* st) {
     st->cr();
   }
 
+  // STEP("printing number of open file descriptors")
+  #ifndef _WIN32
+    os::print_open_file_descriptors(st);
+    st->cr();
+  #endif
+
   // Take heap lock over heap, GC and metaspace printing so that information
   // is consistent.
   if (Universe::is_fully_initialized()) {