8262955: Unify os::fork_and_exec() across Posix platforms

Reviewed-by: dholmes, hseigel

src/hotspot/os/aix/os_aix.cpp

@@ -108,7 +108,6 @@
 #include <sys/types.h>
 #include <sys/utsname.h>
 #include <sys/vminfo.h>
-#include <sys/wait.h>
 
 // Missing prototypes for various system APIs.
 extern "C"
@@ -3150,64 +3149,6 @@ size_t os::current_stack_size() {
   return s;
 }
 
-extern char** environ;
-
-// Run the specified command in a separate process. Return its exit value,
-// or -1 on failure (e.g. can't fork a new process).
-// Unlike system(), this function can be called from signal handler. It
-// doesn't block SIGINT et al.
-int os::fork_and_exec(char* cmd, bool use_vfork_if_available) {
-  char* argv[4] = { (char*)"sh", (char*)"-c", cmd, NULL};
-
-  pid_t pid = fork();
-
-  if (pid < 0) {
-    // fork failed
-    return -1;
-
-  } else if (pid == 0) {
-    // child process
-
-    // Try to be consistent with system(), which uses "/usr/bin/sh" on AIX.
-    execve("/usr/bin/sh", argv, environ);
-
-    // execve failed
-    _exit(-1);
-
-  } else {
-    // copied from J2SE ..._waitForProcessExit() in UNIXProcess_md.c; we don't
-    // care about the actual exit code, for now.
-
-    int status;
-
-    // Wait for the child process to exit. This returns immediately if
-    // the child has already exited. */
-    while (waitpid(pid, &status, 0) < 0) {
-      switch (errno) {
-        case ECHILD: return 0;
-        case EINTR: break;
-        default: return -1;
-      }
-    }
-
-    if (WIFEXITED(status)) {
-      // The child exited normally; get its exit code.
-      return WEXITSTATUS(status);
-    } else if (WIFSIGNALED(status)) {
-      // The child exited because of a signal.
-      // The best value to return is 0x80 + signal number,
-      // because that is what all Unix shells do, and because
-      // it allows callers to distinguish between process exit and
-      // process death by signal.
-      return 0x80 + WTERMSIG(status);
-    } else {
-      // Unknown exit code; pass it through.
-      return status;
-    }
-  }
-  return -1;
-}
-
 // Get the default path to the core file
 // Returns the length of the string
 int os::get_core_path(char* buffer, size_t bufferSize) {

src/hotspot/os/bsd/os_bsd.cpp

@@ -93,7 +93,6 @@
 # include <sys/time.h>
 # include <sys/times.h>
 # include <sys/types.h>
-# include <sys/wait.h>
 # include <time.h>
 # include <unistd.h>
 
@@ -2610,80 +2609,6 @@ void os::pause() {
   }
 }
 
-// Darwin has no "environ" in a dynamic library.
-#ifdef __APPLE__
-  #include <crt_externs.h>
-  #define environ (*_NSGetEnviron())
-#else
-extern char** environ;
-#endif
-
-// Run the specified command in a separate process. Return its exit value,
-// or -1 on failure (e.g. can't fork a new process).
-// Unlike system(), this function can be called from signal handler. It
-// doesn't block SIGINT et al.
-int os::fork_and_exec(char* cmd, bool use_vfork_if_available) {
-  const char * argv[4] = {"sh", "-c", cmd, NULL};
-
-  // fork() in BsdThreads/NPTL is not async-safe. It needs to run
-  // pthread_atfork handlers and reset pthread library. All we need is a
-  // separate process to execve. Make a direct syscall to fork process.
-  // On IA64 there's no fork syscall, we have to use fork() and hope for
-  // the best...
-  pid_t pid = fork();
-
-  if (pid < 0) {
-    // fork failed
-    return -1;
-
-  } else if (pid == 0) {
-    // child process
-
-    // execve() in BsdThreads will call pthread_kill_other_threads_np()
-    // first to kill every thread on the thread list. Because this list is
-    // not reset by fork() (see notes above), execve() will instead kill
-    // every thread in the parent process. We know this is the only thread
-    // in the new process, so make a system call directly.
-    // IA64 should use normal execve() from glibc to match the glibc fork()
-    // above.
-    execve("/bin/sh", (char* const*)argv, environ);
-
-    // execve failed
-    _exit(-1);
-
-  } else  {
-    // copied from J2SE ..._waitForProcessExit() in UNIXProcess_md.c; we don't
-    // care about the actual exit code, for now.
-
-    int status;
-
-    // Wait for the child process to exit.  This returns immediately if
-    // the child has already exited. */
-    while (waitpid(pid, &status, 0) < 0) {
-      switch (errno) {
-      case ECHILD: return 0;
-      case EINTR: break;
-      default: return -1;
-      }
-    }
-
-    if (WIFEXITED(status)) {
-      // The child exited normally; get its exit code.
-      return WEXITSTATUS(status);
-    } else if (WIFSIGNALED(status)) {
-      // The child exited because of a signal
-      // The best value to return is 0x80 + signal number,
-      // because that is what all Unix shells do, and because
-      // it allows callers to distinguish between process exit and
-      // process death by signal.
-      return 0x80 + WTERMSIG(status);
-    } else {
-      // Unknown exit code; pass it through
-      return status;
-    }
-  }
-}
-
 // Get the kern.corefile setting, or otherwise the default path to the core file
 // Returns the length of the string
 int os::get_core_path(char* buffer, size_t bufferSize) {

src/hotspot/os/linux/os_linux.cpp

@@ -97,7 +97,6 @@
 # include <sys/times.h>
 # include <sys/utsname.h>
 # include <sys/socket.h>
-# include <sys/wait.h>
 # include <pwd.h>
 # include <poll.h>
 # include <fcntl.h>
@@ -5219,68 +5218,6 @@ void os::pause() {
   }
 }
 
-extern char** environ;
-
-// Run the specified command in a separate process. Return its exit value,
-// or -1 on failure (e.g. can't fork a new process).
-// Unlike system(), this function can be called from signal handler. It
-// doesn't block SIGINT et al.
-int os::fork_and_exec(char* cmd, bool use_vfork_if_available) {
-  const char * argv[4] = {"sh", "-c", cmd, NULL};
-
-  pid_t pid ;
-
-  if (use_vfork_if_available) {
-    pid = vfork();
-  } else {
-    pid = fork();
-  }
-
-  if (pid < 0) {
-    // fork failed
-    return -1;
-
-  } else if (pid == 0) {
-    // child process
-
-    execve("/bin/sh", (char* const*)argv, environ);
-
-    // execve failed
-    _exit(-1);
-
-  } else  {
-    // copied from J2SE ..._waitForProcessExit() in UNIXProcess_md.c; we don't
-    // care about the actual exit code, for now.
-
-    int status;
-
-    // Wait for the child process to exit.  This returns immediately if
-    // the child has already exited. */
-    while (waitpid(pid, &status, 0) < 0) {
-      switch (errno) {
-      case ECHILD: return 0;
-      case EINTR: break;
-      default: return -1;
-      }
-    }
-
-    if (WIFEXITED(status)) {
-      // The child exited normally; get its exit code.
-      return WEXITSTATUS(status);
-    } else if (WIFSIGNALED(status)) {
-      // The child exited because of a signal
-      // The best value to return is 0x80 + signal number,
-      // because that is what all Unix shells do, and because
-      // it allows callers to distinguish between process exit and
-      // process death by signal.
-      return 0x80 + WTERMSIG(status);
-    } else {
-      // Unknown exit code; pass it through
-      return status;
-    }
-  }
-}
-
 // Get the default path to the core file
 // Returns the length of the string
 int os::get_core_path(char* buffer, size_t bufferSize) {

src/hotspot/os/posix/os_posix.cpp

@@ -51,11 +51,17 @@
 #include <signal.h>
 #include <sys/mman.h>
 #include <sys/resource.h>
+#include <sys/types.h>
 #include <sys/utsname.h>
+#include <sys/wait.h>
 #include <time.h>
 #include <unistd.h>
 #include <utmpx.h>
 
+#ifdef __APPLE__
+  #include <crt_externs.h>
+#endif
+
 #define ROOT_UID 0
 
 #ifndef MAP_ANONYMOUS
@@ -1765,3 +1771,75 @@ int os::PlatformMonitor::wait(jlong millis) {
     return OS_OK;
   }
 }
+
+// Darwin has no "environ" in a dynamic library.
+#ifdef __APPLE__
+  #define environ (*_NSGetEnviron())
+#else
+  extern char** environ;
+#endif
+
+char** os::get_environ() { return environ; }
+
+// Run the specified command in a separate process. Return its exit value,
+// or -1 on failure (e.g. can't fork a new process).
+// Notes: -Unlike system(), this function can be called from signal handler. It
+//         doesn't block SIGINT et al.
+//        -this function is unsafe to use in non-error situations, mainly
+//         because the child process will inherit all parent descriptors.
+int os::fork_and_exec(const char* cmd, bool prefer_vfork) {
+  const char * argv[4] = {"sh", "-c", cmd, NULL};
+
+  pid_t pid ;
+
+  char** env = os::get_environ();
+
+  // Use always vfork on AIX, since its safe and helps with analyzing OOM situations.
+  // Otherwise leave it up to the caller.
+  AIX_ONLY(prefer_vfork = true;)
+  pid = prefer_vfork ? ::vfork() : ::fork();
+
+  if (pid < 0) {
+    // fork failed
+    return -1;
+
+  } else if (pid == 0) {
+    // child process
+
+    ::execve("/bin/sh", (char* const*)argv, env);
+
+    // execve failed
+    ::_exit(-1);
+
+  } else  {
+    // copied from J2SE ..._waitForProcessExit() in UNIXProcess_md.c; we don't
+    // care about the actual exit code, for now.
+
+    int status;
+
+    // Wait for the child process to exit.  This returns immediately if
+    // the child has already exited. */
+    while (::waitpid(pid, &status, 0) < 0) {
+      switch (errno) {
+      case ECHILD: return 0;
+      case EINTR: break;
+      default: return -1;
+      }
+    }
+
+    if (WIFEXITED(status)) {
+      // The child exited normally; get its exit code.
+      return WEXITSTATUS(status);
+    } else if (WIFSIGNALED(status)) {
+      // The child exited because of a signal
+      // The best value to return is 0x80 + signal number,
+      // because that is what all Unix shells do, and because
+      // it allows callers to distinguish between process exit and
+      // process death by signal.
+      return 0x80 + WTERMSIG(status);
+    } else {
+      // Unknown exit code; pass it through
+      return status;
+    }
+  }
+}

src/hotspot/os/windows/os_windows.cpp

@@ -266,6 +266,8 @@ bool os::unsetenv(const char* name) {
   return (SetEnvironmentVariable(name, NULL) == TRUE);
 }
 
+char** os::get_environ() { return _environ; }
+
 // No setuid programs under Windows.
 bool os::have_special_privileges() {
   return false;
@@ -5512,7 +5514,7 @@ int os::PlatformMonitor::wait(jlong millis) {
 
 // Run the specified command in a separate process. Return its exit value,
 // or -1 on failure (e.g. can't create a new process).
-int os::fork_and_exec(char* cmd, bool use_vfork_if_available) {
+int os::fork_and_exec(const char* cmd, bool dummy /* ignored */) {
   STARTUPINFO si;
   PROCESS_INFORMATION pi;
   DWORD exit_code;

src/hotspot/share/jfr/periodic/jfrOSInterface.cpp

@@ -34,14 +34,6 @@
 #include "utilities/ostream.hpp"
 
 #include <stdlib.h> // for environment variables
-#ifdef __APPLE__
-#include <crt_externs.h>
-#define environ (*_NSGetEnviron())
-#endif
-
-#ifndef environ
-extern char** environ;
-#endif
 
 static JfrOSInterface* _instance = NULL;
 
@@ -281,14 +273,14 @@ const char* JfrOSInterface::virtualization_name() {
 }
 
 int JfrOSInterface::generate_initial_environment_variable_events() {
-  if (environ == NULL) {
+  if (os::get_environ() == NULL) {
     return OS_ERR;
   }
 
   if (EventInitialEnvironmentVariable::is_enabled()) {
     // One time stamp for all events, so they can be grouped together
     JfrTicks time_stamp = JfrTicks::now();
-    for (char** p = environ; *p != NULL; p++) {
+    for (char** p = os::get_environ(); *p != NULL; p++) {
       char* variable = *p;
       char* equal_sign = strchr(variable, '=');
       if (equal_sign != NULL) {

src/hotspot/share/runtime/os.hpp

@@ -182,6 +182,8 @@ class os: AllStatic {
 
   // unset environment variable
   static bool unsetenv(const char* name);
+  // Get environ pointer, platform independently
+  static char** get_environ();
 
   static bool have_special_privileges();
 
@@ -501,8 +503,12 @@ class os: AllStatic {
 
   static bool message_box(const char* title, const char* message);
 
-  // run cmd in a separate process and return its exit code; or -1 on failures
+  // run cmd in a separate process and return its exit code; or -1 on failures.
-  static int fork_and_exec(char *cmd, bool use_vfork_if_available = false);
+  // Note: only safe to use in fatal error situations.
+  // The "prefer_vfork" argument is only used on POSIX platforms to
+  // indicate whether vfork should be used instead of fork to spawn the
+  // child process (ignored on AIX, which always uses vfork).
+  static int fork_and_exec(const char *cmd, bool prefer_vfork = false);
 
   // Call ::exit() on all platforms but Windows
   static void exit(int num);