Enable customization of the system temp path on Linux

src/hotspot/os/linux/globals_linux.hpp

@@ -107,6 +107,10 @@
   develop(bool, DelayThreadStartALot, false,                            \
           "Artificially delay thread starts randomly for testing.")     \
                                                                         \
+  diagnostic(ccstr, SystemTempPath, NULL,                               \
+          "An alternative path to use for the system's temporary "      \
+          "directory instead of hardcoded paths like /tmp ")            \
+                                                                        \
 
 
 // end of RUNTIME_OS_FLAGS

src/hotspot/os/linux/os_linux.cpp

@@ -1437,7 +1437,54 @@ const char* os::dll_file_extension() { return ".so"; }
 
 // This must be hard coded because it's the system's temporary
 // directory not the java application's temp directory, ala java.io.tmpdir.
-const char* os::get_temp_directory() { return "/tmp"; }
+// Use half of PATH_MAX characters for the custom temporary path to allow
+// paths of length (PATH_MAX / 2) to be appended to the custom temp path.
+#define MAX_CACHED_TEMP_PATH_LENGTH (PATH_MAX / 2)
+
+// This method allows for overriding the system's temporary directory via the -XX:SystemTempPath option
+const char* os::get_temp_directory() {
+  static const char* cached_temp_path = NULL;
+  static const char* default_tmp_path = "/tmp";
+
+  if (cached_temp_path == NULL) {
+    bool use_default_tmp_path = true;
+
+    if (SystemTempPath != NULL) {
+      size_t new_tmp_path_length = strlen(SystemTempPath);
+
+      assert(new_tmp_path_length > 0, "SystemTempPath must have positive length");
+      assert(new_tmp_path_length < MAX_CACHED_TEMP_PATH_LENGTH, "SystemTempPath exceeds allowed length");
+
+      if (new_tmp_path_length > 0 && new_tmp_path_length < MAX_CACHED_TEMP_PATH_LENGTH) {
+        struct stat stat_buf;
+        bool path_exists = os::stat(SystemTempPath, &stat_buf) == 0;
+
+        if (path_exists) {
+          if (S_ISDIR(stat_buf.st_mode)) {
+            if (0 == access(SystemTempPath, R_OK | W_OK)) {
+              use_default_tmp_path = false;
+            } else {
+              warning("Cannot access the specified SystemTempPath");
+            }
+          } else {
+            warning("SystemTempPath must be a directory");
+          }
+        } else {
+          warning("Cannot find the specified SystemTempPath");
+        }
+      } else {
+        warning("Invalid SystemTempPath length");
+      }
+
+      if (use_default_tmp_path) {
+        warning("Ignoring SystemTempPath and using the default temp path");
+      }
+    }
+
+    cached_temp_path = use_default_tmp_path ? default_tmp_path : SystemTempPath;
+  }
+  return cached_temp_path;
+}
 
 // check if addr is inside libjvm.so
 bool os::address_is_in_vm(address addr) {

src/hotspot/os/posix/perfMemory_posix.cpp

@@ -127,15 +127,19 @@ static void save_memory_to_file(char* addr, size_t size) {
 // return the user specific temporary directory name.
 // the caller is expected to free the allocated memory.
 //
+#if defined(LINUX)
+#define TMP_BUFFER_LEN (PATH_MAX / 2)
+#else
 #define TMP_BUFFER_LEN (4+22)
+#endif
 static char* get_user_tmp_dir(const char* user, int vmid, int nspid) {
   char* tmpdir = (char *)os::get_temp_directory();
 #if defined(LINUX)
   // On linux, if containerized process, get dirname of
   // /proc/{vmid}/root/tmp/{PERFDATA_NAME_user}
   // otherwise /tmp/{PERFDATA_NAME_user}
   char buffer[TMP_BUFFER_LEN];
-  assert(strlen(tmpdir) == 4, "No longer using /tmp - update buffer size");
+  assert((strlen(tmpdir) + 22) < TMP_BUFFER_LEN, "Insufficient buffer size for temp dir");
 
   if (nspid != -1) {
     jio_snprintf(buffer, TMP_BUFFER_LEN, "/proc/%d/root%s", vmid, tmpdir);