Fix spurious errors when writing to the child process stdin under Unix.

Since the child pipe was made non-blocking in r65993, it became possible to
write to child process without deadlocking when the pipe became full. However
this still resulted in an error from wxFileOutputStream as it didn't handle
EAGAIN returned from write() any differently than any other error, even though
it is an expected situation in this particular case.

Change Unix wxExecute() to use wxPipeOutputStream which ignores EAGAIN unlike
wxFileOutputStream to fix this.

See #12636.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66152 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -410,6 +410,10 @@ All:
 - Added wxThread::OnKill() and OnDelete() callbacks.
 - Added wxFile::GetLastError() and ClearLastError() (ryazanov).
 
+Unix:
+
+- Fix spurious errors when writing to child process pipe (ryazanov).
+
 All (GUI):
 
 - Added wxRichMessageDialog (Rickard Westerlund, GSoC 2010 project).

include/wx/unix/pipe.h

@@ -118,6 +118,20 @@ public:
     virtual bool CanRead() const;
 };
 
+// ----------------------------------------------------------------------------
+// wxPipeOutputStream: stream for writing to a pipe
+// ----------------------------------------------------------------------------
+
+class wxPipeOutputStream : public wxFileOutputStream
+{
+public:
+    wxPipeOutputStream(int fd) : wxFileOutputStream(fd) { }
+
+    // Override the base class version to ignore "pipe full" errors: this is
+    // not an error for this class.
+    size_t OnSysWrite(const void *buffer, size_t size);
+};
+
 #endif // wxUSE_STREAMS && wxUSE_FILE
 
 #endif // _WX_UNIX_PIPE_H_

src/unix/utilsunx.cpp

@@ -337,6 +337,45 @@ bool wxPipeInputStream::CanRead() const
     }
 }
 
+size_t wxPipeOutputStream::OnSysWrite(const void *buffer, size_t size)
+{
+    // We need to suppress error logging here, because on writing to a pipe
+    // which is full, wxFile::Write reports a system error. However, this is
+    // not an extraordinary situation, and it should not be reported to the
+    // user (but if really needed, the program can recognize it by checking
+    // whether LastRead() == 0.) Other errors will be reported below.
+    size_t ret;
+    {
+        wxLogNull logNo;
+        ret = m_file->Write(buffer, size);
+    }
+
+    switch ( m_file->GetLastError() )
+    {
+       // pipe is full
+#ifdef EAGAIN
+       case EAGAIN:
+#endif
+#if defined(EWOULDBLOCK) && (EWOULDBLOCK != EAGAIN)
+       case EWOULDBLOCK:
+#endif
+           // do not treat it as an error
+           m_file->ClearLastError();
+           // fall through
+
+       // no error
+       case 0:
+           break;
+
+       // some real error
+       default:
+           wxLogSysError(_("Can't write to child process's stdin"));
+           m_lasterror = wxSTREAM_WRITE_ERROR;
+    }
+
+    return ret;
+}
+
 #endif // HAS_PIPE_STREAMS
 
 // ----------------------------------------------------------------------------
@@ -662,10 +701,11 @@ long wxExecute(char **argv, int flags, wxProcess *process,
                 // it might not be the best idea.
                 wxLogSysError(_("Failed to set up non-blocking pipe, "
                                 "the program might hang."));
+                wxLog::FlushActive();
             }
 
             wxOutputStream *inStream =
-                new wxFileOutputStream(pipeIn.Detach(wxPipe::Write));
+                new wxPipeOutputStream(pipeIn.Detach(wxPipe::Write));
 
             const int fdOut = pipeOut.Detach(wxPipe::Read);
             wxPipeInputStream *outStream = new wxPipeInputStream(fdOut);