X-Git-Url: https://git.saurik.com/apple/security.git/blobdiff_plain/72a12576750f52947eb043106ba5c12c0d07decf..b1ab9ed8d0e0f1c3b66d7daa8fd5564444c56195:/libsecurity_utilities/lib/globalizer.cpp

diff --git a/libsecurity_utilities/lib/globalizer.cpp b/libsecurity_utilities/lib/globalizer.cpp
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+/*
+ * Copyright (c) 2000-2004 Apple Computer, Inc. All Rights Reserved.
+ * 
+ * @APPLE_LICENSE_HEADER_START@
+ * 
+ * This file contains Original Code and/or Modifications of Original Code
+ * as defined in and that are subject to the Apple Public Source License
+ * Version 2.0 (the 'License'). You may not use this file except in
+ * compliance with the License. Please obtain a copy of the License at
+ * http://www.opensource.apple.com/apsl/ and read it before using this
+ * file.
+ * 
+ * The Original Code and all software distributed under the License are
+ * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
+ * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
+ * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
+ * Please see the License for the specific language governing rights and
+ * limitations under the License.
+ * 
+ * @APPLE_LICENSE_HEADER_END@
+ */
+
+
+//
+// globalizer - multiscope globalization services.
+//
+// This is a tentative, partial implementation.
+// Status:
+//	module scope: constructs, optional cleanup
+//	thread scope: constructs, optional cleanup
+//	process scope: not implemented (obsolete implementation, unused)
+//	system scope: not implemented (probably never will)
+//
+// @@@ Assumption: {bool,T*} atomic unless PTHREAD_STRICT
+//
+#include <security_utilities/globalizer.h>
+#include <security_utilities/debugging.h>
+#include <cstdlib>
+#include <stdexcept>
+
+//
+// The Error class thrown if Nexus operations fail
+//
+GlobalNexus::Error::~Error() throw()
+{
+}
+
+
+//
+// The long (and possibly contentious) path of ModuleNexus()
+//
+// Briefly, the trick here is to go through a three-stage sequence
+// to lazily construct a unique singleton object, no matter how many
+// threads all of a sudden decide they need it.
+// State sequence:
+// State 0: pointer == 0, not initialized, idle
+// State 1: pointer == mutexp | 0x1, where mutexp points to a Mutex
+//  used to serialize construction of the singleton object
+// State 2: pointer == &singleton, and we're done
+//
+// TAKE NOTE:
+// This code is optimized with a particular issue in mind: when placed
+// into static storage (as ModuleNexi are wont to), it should not require
+// dynamic initialization. This is important because our code is, in effect,
+// linked into just about every program in the system. The price we pay
+// for this coolness is
+//  (a) This won't work *except* in static storage (not on stack or heap)
+//  (b) We slightly fracture portability (see below)
+// This has been considered Worth It, at least for now. Before you throw
+// up and throw this code out, please try to figure out whether you know
+// the Whole Story. Thank you.
+//
+// WARNING:
+// This code makes the following non-portable assumptions:
+//  (a) NULL == 0 (binary representation of NULL pointer is zero value)
+//	(b) Pointers acquired from new have at least their LSB zero (are at
+//      least two-byte aligned).
+// It seems like it's been a while since anyone made a machine/runtime that
+// violated either of those. But you have been warned.
+//
+void *ModuleNexusCommon::create(void *(*make)())
+{
+    sync++;		// keep mutex alive if needed
+  retry:
+    void *initialPointer = Atomic<void *>::load(pointer);	// latch pointer
+    if (!initialPointer || (uintptr_t(initialPointer) & 0x1)) {
+        Mutex *mutex;
+        if (initialPointer == 0) {
+            mutex = new Mutex;
+            mutex->lock();
+			if (!Atomic<void *>::casb(0, (void *)(uintptr_t(mutex) | 0x1), pointer)) {
+                // somebody beat us to the lead - back off
+                mutex->unlock();
+                delete mutex;
+                goto retry;
+            }
+            // we have the ball
+            try {
+                void *singleton = make();
+                pointer = singleton;
+                // we need a write barrier here, but the mutex->unlock below provides it for free
+            } catch (...) {
+				secdebug("nexus", "ModuleNexus %p construction failed", this);
+                mutex->unlock();
+                if (--sync == 0) {
+                    delete mutex;
+                    pointer = 0;
+                }
+                throw;
+            }
+        } else {
+            mutex = reinterpret_cast<Mutex *>(uintptr_t(initialPointer) & ~0x1);
+            mutex->lock();	// we'll wait here
+        }
+        mutex->unlock();
+        //@@@ retry if not resolved -- or fail here (with "object can't be built")
+        if (--sync == 0)
+            delete mutex;
+    }
+    return pointer;
+}
+
+
+// thread nexus static globals
+ModuleNexus<Mutex> ThreadNexusBase::mInstanceLock;
+
+// Thread nexus globals
+ModuleNexus<RetentionSet> ThreadNexusBase::mInstances;
+
+//
+// Process nexus operation
+//
+ProcessNexusBase::ProcessNexusBase(const char *identifier)
+{
+	const char *env = getenv(identifier);
+	if (env == NULL) {	// perhaps we're first...
+		auto_ptr<Store> store(new Store);
+		char form[2*sizeof(Store *) + 2];
+		sprintf(form, "*%p", &store);
+		setenv(identifier, form, 0);	// do NOT overwrite...
+		env = getenv(identifier);		// ... and refetch to resolve races
+		if (sscanf(env, "*%p", &mStore) != 1)
+			throw std::runtime_error("environment communication failed");
+		if (mStore == store.get())		// we won the race...
+			store.release();			// ... so keep the store
+	} else
+		if (sscanf(env, "*%p", &mStore) != 1)
+			throw std::runtime_error("environment communication failed");
+}