+/*
+ * 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");
+}
projects / apple / security.git / blobdiff