* Syscall.cs: Make all fork(2) and exec(2) functions `private`. It

	  currently isn't safe to call these under *any* circumstances.

svn path=/trunk/mcs/; revision=43324

2 files changed, 34 insertions, 6 deletions

diff --git a/mcs/class/Mono.Posix/Mono.Unix/ChangeLog b/mcs/class/Mono.Posix/Mono.Unix/ChangeLog
index 4bf01251932..c4b5d2502c9 100644
--- a/mcs/class/Mono.Posix/Mono.Unix/ChangeLog
+++ b/mcs/class/Mono.Posix/Mono.Unix/ChangeLog
@@ -1,3 +1,31 @@
+2005-04-20  Jonathan Pryor <jonpryor@vt.edu>
+
+	* Syscall.cs: Make all fork(2) and exec(2) functions `private`.  It
+	  currently isn't safe to call these under *any* circumstances.  See also
+	  68141, and this pertinent quote from Butenhof's 
+	  "Programming with POSIX Threads", p197, s6.1:
+	  
+	      "When a threaded process calls fork to create a child process,
+	      Pthreads specifies that only the thread calling fork exists in the
+	      child. ... Pthreads does not 'terminate' the other threads in a forked
+	      process...They simply cease to exist.  ... This is not a problem if
+	      the child process is about to call exec to run a new program, but if
+	      you use fork to clone a threaded program, beware that you may lose
+	      access to memory, especially heap memory stored only as
+	      thread-specific data values."
+	  
+	  Since P/Invoke currently requires using thread local storage, once you
+	  fork(2) you won't be able to invoke exec(2) from managed code (since that
+	  would require a P/Invoke transition to call exec(2), which would require
+	  TLS, which doesn't exist in the new process).
+	 
+	  This can only be fixed by removing the TLS dependency on P/Invoke, which
+	  isn't a priority (and may not be possible).
+	 
+	  The workaround is to create a C function which does your fork(2)/exec(2)
+	  (and any other functions such as daemon(3)) on your behalf, and P/Invoke
+	  to call this C function.
+
 2005-04-18  Jonathan Pryor <jonpryor@vt.edu>
 
 	* Syscall.cs: Update comment specifying which functions belong in Syscall.
diff --git a/mcs/class/Mono.Posix/Mono.Unix/Syscall.cs b/mcs/class/Mono.Posix/Mono.Unix/Syscall.cs
index ef17f2239aa..bc5317eaeb7 100644
--- a/mcs/class/Mono.Posix/Mono.Unix/Syscall.cs
+++ b/mcs/class/Mono.Posix/Mono.Unix/Syscall.cs
@@ -2329,17 +2329,17 @@ namespace Mono.Unix {
 
 		// TODO: does Mono marshal arrays properly?
 		[DllImport (LIBC, SetLastError=true)]
-		public static extern int execve (string path, string[] argv, string[] envp);
+		private static extern int execve (string path, string[] argv, string[] envp);
 
 		[DllImport (LIBC, SetLastError=true)]
-		public static extern int fexecve (int fd, string[] argv, string[] envp);
+		private static extern int fexecve (int fd, string[] argv, string[] envp);
 
 		[DllImport (LIBC, SetLastError=true)]
-		public static extern int execv (string path, string[] argv);
+		private static extern int execv (string path, string[] argv);
 
 		// TODO: execle, execl, execlp
 		[DllImport (LIBC, SetLastError=true)]
-		public static extern int execvp (string path, string[] argv);
+		private static extern int execvp (string path, string[] argv);
 
 		[DllImport (LIBC, SetLastError=true)]
 		public static extern int nice (int inc);
@@ -2488,14 +2488,14 @@ namespace Mono.Unix {
 		[DllImport (LIBC, SetLastError=true)]
 		[Obsolete ("DO NOT directly call fork(2); it bypasses essential " + 
 				"shutdown code.\nUse System.Diagnostics.Process instead")]
-		public static extern int fork ();
+		private static extern int fork ();
 
 		// vfork(2)
 		//    pid_t vfork(void);
 		[DllImport (LIBC, SetLastError=true)]
 		[Obsolete ("DO NOT directly call vfork(2); it bypasses essential " + 
 				"shutdown code.\nUse System.Diagnostics.Process instead")]
-		public static extern int vfork ();
+		private static extern int vfork ();
 
 		[DllImport (LIBC, SetLastError=true, EntryPoint="ttyname")]
 		private static extern IntPtr sys_ttyname (int fd);