atomicio: provide atomic read and write functions.

These functions keep trying to read and write until all data has been
transferred, or an error occurrs.  In the case where an end of file
hasn't been reached, but all of the bytes have not been read/written,
try again.  On EINTR, try again.

1 files changed, 92 insertions, 0 deletions

diff --git a/src/base/atomicio.cc b/src/base/atomicio.cc
new file mode 100644
index 000000000..3f3e6d6f0
--- /dev/null
+++ b/src/base/atomicio.cc
@@ -0,0 +1,92 @@
+/*
+ * Copyright (c) 2008 The Hewlett-Packard Development Company
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met: redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer;
+ * redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution;
+ * neither the name of the copyright holders nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ * Authors: Nathan Binkert
+ */
+
+#include <cerrno>
+#include <cstdio>
+
+#include "base/atomicio.hh"
+
+ssize_t
+atomic_read(int fd, void *s, size_t n)
+{
+    char *p = reinterpret_cast<char *>(s);
+    ssize_t pos = 0;
+
+    // Keep reading until we've gotten all of the data.
+    while (n > pos) {
+        ssize_t result = read(fd, p + pos, n - pos);
+
+        // We didn't get any more data, so we should probably punt,
+        // otherwise we'd just keep spinning
+        if (result == 0)
+            break;
+
+        // If there was an error, try again on EINTR/EAGAIN, pass the
+        // error up otherwise.
+        if (result == -1) {
+            if (errno == EINTR || errno == EAGAIN)
+                continue;
+            return result;
+        }
+
+        pos += result;
+    }
+
+    return pos;
+}
+
+ssize_t
+atomic_write(int fd, const void *s, size_t n)
+{
+    const char *p = reinterpret_cast<const char *>(s);
+    ssize_t pos = 0;
+
+    // Keep writing until we've written all of the data
+    while (n > pos) {
+        ssize_t result = write(fd, p + pos, n - pos);
+
+        // We didn't manage to write anything this time, so we should
+        // probably punt, otherwise we'd just keep spinning
+        if (result == 0)
+            break;
+
+        // If there was an error, try again on EINTR/EAGAIN, pass the
+        // error up otherwise.
+        if (result == -1) {
+            if (errno == EINTR || errno == EAGAIN)
+                continue;
+            return result;
+        }
+
+        pos += result;
+    }
+
+    return pos;
+}