using the resultant compiler to build a copy of LLVM with multithreading
support.
-.. _startmultithreaded:
-
-Entering and Exiting Multithreaded Mode
----------------------------------------
-
-In order to properly protect its internal data structures while avoiding
-excessive locking overhead in the single-threaded case, the LLVM must intialize
-certain data structures necessary to provide guards around its internals. To do
-so, the client program must invoke ``llvm_start_multithreaded()`` before making
-any concurrent LLVM API calls. To subsequently tear down these structures, use
-the ``llvm_stop_multithreaded()`` call. You can also use the
-``llvm_is_multithreaded()`` call to check the status of multithreaded mode.
-
-Note that both of these calls must be made *in isolation*. That is to say that
-no other LLVM API calls may be executing at any time during the execution of
-``llvm_start_multithreaded()`` or ``llvm_stop_multithreaded``. It is the
-client's responsibility to enforce this isolation.
-
-The return value of ``llvm_start_multithreaded()`` indicates the success or
-failure of the initialization. Failure typically indicates that your copy of
-LLVM was built without multithreading support, typically because GCC atomic
-intrinsics were not found in your system compiler. In this case, the LLVM API
-will not be safe for concurrent calls. However, it *will* be safe for hosting
-threaded applications in the JIT, though :ref:`care must be taken
-<jitthreading>` to ensure that side exits and the like do not accidentally
-result in concurrent LLVM API calls.
-
.. _shutdown:
Ending Execution with ``llvm_shutdown()``
-----------------------------------------
When you are done using the LLVM APIs, you should call ``llvm_shutdown()`` to
-deallocate memory used for internal structures. This will also invoke
-``llvm_stop_multithreaded()`` if LLVM is operating in multithreaded mode. As
-such, ``llvm_shutdown()`` requires the same isolation guarantees as
-``llvm_stop_multithreaded()``.
-
-Note that, if you use scope-based shutdown, you can use the
-``llvm_shutdown_obj`` class, which calls ``llvm_shutdown()`` in its destructor.
+deallocate memory used for internal structures.
.. _managedstatic:
------------------------------------------
``ManagedStatic`` is a utility class in LLVM used to implement static
-initialization of static resources, such as the global type tables. Before the
-invocation of ``llvm_shutdown()``, it implements a simple lazy initialization
-scheme. Once ``llvm_start_multithreaded()`` returns, however, it uses
+initialization of static resources, such as the global type tables. In a
+single-threaded environment, it implements a simple lazy initialization scheme.
+When LLVM is compiled with support for multi-threading, however, it uses
double-checked locking to implement thread-safe lazy initialization.
-Note that, because no other threads are allowed to issue LLVM API calls before
-``llvm_start_multithreaded()`` returns, it is possible to have
-``ManagedStatic``\ s of ``llvm::sys::Mutex``\ s.
-
.. _llvmcontext:
Achieving Isolation with ``LLVMContext``
* @{
*/
-/** Allocate and initialize structures needed to make LLVM safe for
- multithreading. The return value indicates whether multithreaded
- initialization succeeded. Must be executed in isolation from all
- other LLVM api calls.
- @see llvm::llvm_start_multithreaded */
+/** Deprecated: Multi-threading can only be enabled/disabled with the compile
+ time define LLVM_ENABLE_THREADS. This function always returns
+ LLVMIsMultithreaded(). */
LLVMBool LLVMStartMultithreaded(void);
-/** Deallocate structures necessary to make LLVM safe for multithreading.
- Must be executed in isolation from all other LLVM api calls.
- @see llvm::llvm_stop_multithreaded */
+/** Deprecated: Multi-threading can only be enabled/disabled with the compile
+ time define LLVM_ENABLE_THREADS. */
void LLVMStopMultithreaded(void);
/** Check whether LLVM is executing in thread-safe mode or not.
/// llvm_shutdown() when it is destroyed.
struct llvm_shutdown_obj {
llvm_shutdown_obj() { }
- explicit llvm_shutdown_obj(bool multithreaded) {
- if (multithreaded) llvm_start_multithreaded();
- }
~llvm_shutdown_obj() { llvm_shutdown(); }
};
//
//===----------------------------------------------------------------------===//
//
-// TThis file defines llvm_start_multithreaded() and friends.
+// This file declares helper functions for running LLVM in a multi-threaded
+// environment.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_THREADING_H
#define LLVM_SUPPORT_THREADING_H
-namespace llvm {
- /// llvm_start_multithreaded - Allocate and initialize structures needed to
- /// make LLVM safe for multithreading. The return value indicates whether
- /// multithreaded initialization succeeded. LLVM will still be operational
- /// on "failed" return, and will still be safe for hosting threading
- /// applications in the JIT, but will not be safe for concurrent calls to the
- /// LLVM APIs.
- /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
- bool llvm_start_multithreaded();
-
- /// llvm_stop_multithreaded - Deallocate structures necessary to make LLVM
- /// safe for multithreading.
- /// THIS MUST EXECUTE IN ISOLATION FROM ALL OTHER LLVM API CALLS.
- void llvm_stop_multithreaded();
+#include "llvm/Support/Mutex.h"
- /// llvm_is_multithreaded - Check whether LLVM is executing in thread-safe
- /// mode or not.
+namespace llvm {
+ /// Returns true if LLVM is compiled with support for multi-threading, and
+ /// false otherwise.
bool llvm_is_multithreaded();
/// llvm_execute_on_thread - Execute the given \p UserFn on a separate
/*===-- Threading ------------------------------------------------------===*/
LLVMBool LLVMStartMultithreaded() {
- return llvm_start_multithreaded();
+ return LLVMIsMultithreaded();
}
void LLVMStopMultithreaded() {
- llvm_stop_multithreaded();
}
LLVMBool LLVMIsMultithreaded() {
//
//===----------------------------------------------------------------------===//
//
-// This file implements llvm_start_multithreaded() and friends.
+// This file defines helper functions for running LLVM in a multi-threaded
+// environment.
//
//===----------------------------------------------------------------------===//
using namespace llvm;
-static bool multithreaded_mode = false;
-
-bool llvm::llvm_start_multithreaded() {
+bool llvm::llvm_is_multithreaded() {
#if LLVM_ENABLE_THREADS != 0
- assert(!multithreaded_mode && "Already multithreaded!");
- multithreaded_mode = true;
-
- // We fence here to ensure that all initialization is complete BEFORE we
- // return from llvm_start_multithreaded().
- sys::MemoryFence();
return true;
#else
return false;
#endif
}
-void llvm::llvm_stop_multithreaded() {
-#if LLVM_ENABLE_THREADS != 0
- assert(multithreaded_mode && "Not currently multithreaded!");
-
- // We fence here to insure that all threaded operations are complete BEFORE we
- // return from llvm_stop_multithreaded().
- sys::MemoryFence();
-
- multithreaded_mode = false;
-#endif
-}
-
-bool llvm::llvm_is_multithreaded() {
- return multithreaded_mode;
-}
-
#if LLVM_ENABLE_THREADS != 0 && defined(HAVE_PTHREAD_H)
#include <pthread.h>
void *p1 = test1::allocate_stack(a1);
void *p2 = test1::allocate_stack(a2);
- llvm_start_multithreaded();
pthread_t t1, t2;
pthread_create(&t1, &a1, test1::helper, nullptr);
pthread_create(&t2, &a2, test1::helper, nullptr);
pthread_join(t2, nullptr);
free(p1);
free(p2);
- llvm_stop_multithreaded();
}
#endif
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