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// file : build2/context.hxx -*- C++ -*-
// copyright : Copyright (c) 2014-2017 Code Synthesis Ltd
// license : MIT; see accompanying LICENSE file
#ifndef BUILD2_CONTEXT_HXX
#define BUILD2_CONTEXT_HXX
#include <build2/types.hxx>
#include <build2/utility.hxx>
#include <build2/scope.hxx>
#include <build2/variable.hxx>
#include <build2/operation.hxx>
#include <build2/scheduler.hxx>
namespace build2
{
// Main (and only) scheduler. Started up and shut down in main().
//
extern scheduler sched;
// In order to perform each operation the build system goes through the
// following phases:
//
// load - load the buildfiles
// match - search prerequisites and match rules
// execute - execute the matched rule
//
// The build system starts with a "serial load" phase and then continues
// with parallel search and execute. Match, however, can be interrupted
// both with load and execute.
//
// Match can be interrupted with "exclusive load" in order to load
// additional buildfiles. Similarly, it can be interrupted with (parallel)
// execute in order to build targetd required to complete the match (for
// example, generated source code or source code generators themselves.
//
// Such interruptions are performed by phase change that is protected by
// phase_mutex (which is also used to synchronize the state changes between
// phases).
//
// Serial load can perform arbitrary changes to the model. Exclusive load,
// however, can only perform "island appends". That is, it can create new
// "nodes" (variables, scopes, etc) but not change already existing nodes or
// invalidate any references to such (the idea here is that one should be
// able to load additional buildfiles as long as they don't interfere with
// the existing build state). The "islands" are identified by the
// load_generation number (0 for initial/serial load). It is incremented in
// case of a phase switch and is stored in various "nodes" (variables, etc)
// to allow modifications "within the islands".
//
extern run_phase phase;
extern size_t load_generation;
// A "tri-mutex" that keeps all the threads in one of the three phases. When
// a thread wants to switch a phase, it has to wait for all the other
// threads to do the same (or release their phase locks). The load phase is
// exclusive.
//
// The interleaving match and execute is interesting: during match we read
// the "external state" (e.g., filesystem entries, modifications times, etc)
// and capture it in the "internal state" (our dependency graph). During
// execute we are modifying the external state with controlled modifications
// of the internal state to reflect the changes (e.g., update mtimes). If
// you think about it, it's pretty clear that we cannot safely perform both
// of these actions simultaneously. A good example would be running a code
// generator and header dependency extraction simultaneously: the extraction
// process may pick up headers as they are being generated. As a result, we
// either have everyone treat the external state as read-only or write-only.
//
class phase_mutex
{
public:
// Acquire a phase lock potentially blocking (unless already in the
// desired phase) until switching to the desired phase is possible.
//
void
lock (run_phase);
// Release the phase lock potentially allowing (unless there are other
// locks on this phase) switching to a different phase.
//
void
unlock (run_phase);
// Switch from one phase to another. Semantically, just unlock() followed
// by lock() but more efficient.
//
void
relock (run_phase unlock, run_phase lock);
private:
friend struct phase_lock;
friend struct phase_unlock;
friend struct phase_switch;
phase_mutex (): lc_ (0), mc_ (0), ec_ (0) {phase = run_phase::load;}
static phase_mutex instance;
private:
// We have a counter for each phase which represents the number of threads
// in or waiting for this phase.
//
// We use condition variables to wait for a phase switch. The load phase
// is exclusive so we have a separate mutex to serialize it (think of it
// as a second level locking).
//
// When the mutex is unlocked (all three counters become zero, the phase
// is always changed to load (this is also the initial state).
//
mutex m_;
size_t lc_;
size_t mc_;
size_t ec_;
condition_variable lv_;
condition_variable mv_;
condition_variable ev_;
mutex lm_;
};
// Grab a new phase lock releasing it on destruction. The lock can be
// "owning" or "referencing" (recursive).
//
// On the referencing semantics: If there is already an instance of
// phase_lock in this thread, then the new instance simply references it.
//
// The reason for this semantics is to support the following scheduling
// pattern (in actual code we use wait_guard to RAII it):
//
// atomic_count task_count (0);
//
// {
// phase_lock l (run_phase::match); // (1)
//
// for (...)
// {
// sched.async (task_count,
// [] (...)
// {
// phase_lock pl (run_phase::match); // (2)
// ...
// },
// ...);
// }
// }
//
// sched.wait (task_count); // (3)
//
// Here is what's going on here:
//
// 1. We first get a phase lock "for ourselves" since after the first
// iteration of the loop, things may become asynchronous (including
// attempts to switch the phase and modify the structure we are iteration
// upon).
//
// 2. The task can be queued or it can be executed synchronously inside
// async() (refer to the scheduler class for details on this semantics).
//
// If this is an async()-synchronous execution, then the task will create
// a referencing phase_lock. If, however, this is a queued execution
// (including wait()-synchronous), then the task will create a top-level
// phase_lock.
//
// Note that we only acquire the lock once the task starts executing
// (there is no reason to hold the lock while the task is sitting in the
// queue). This optimization assumes that whatever else we pass to the
// task (for example, a reference to a target) is stable (in other words,
// such a reference cannot become invalid).
//
// 3. Before calling wait(), we release our phase lock to allow switching
// the phase.
//
struct phase_lock
{
explicit phase_lock (run_phase);
~phase_lock ();
phase_lock (phase_lock&&) = delete;
phase_lock (const phase_lock&) = delete;
phase_lock& operator= (phase_lock&&) = delete;
phase_lock& operator= (const phase_lock&) = delete;
run_phase p;
static
#ifdef __cpp_thread_local
thread_local
#else
__thread
#endif
phase_lock* instance;
};
// Assuming we have a lock on the current phase, temporarily release it
// and reacquire on destruction.
//
struct phase_unlock
{
phase_unlock (bool unlock = true);
~phase_unlock ();
phase_lock* l;
};
// Assuming we have a lock on the current phase, temporarily switch to a
// new phase and switch back on destruction.
//
struct phase_switch
{
explicit phase_switch (run_phase);
~phase_switch ();
run_phase o, n;
};
// Wait for a task count optionally and temporarily unlocking the phase.
//
struct wait_guard
{
~wait_guard () noexcept (false);
explicit
wait_guard (atomic_count& task_count,
bool phase = false);
wait_guard (size_t start_count,
atomic_count& task_count,
bool phase = false);
void
wait ();
size_t start_count;
atomic_count* task_count;
bool phase;
};
// Cached variables.
//
extern const variable* var_src_root;
extern const variable* var_out_root;
extern const variable* var_src_base;
extern const variable* var_out_base;
extern const variable* var_project;
extern const variable* var_amalgamation;
extern const variable* var_subprojects;
extern const variable* var_import_target; // import.target
// Current action (meta/operation).
//
// The names unlike info are available during boot but may not yet be
// lifted. The name is always for an outer operation (or meta operation
// that hasn't been recognized as such yet).
//
extern const string* current_mname;
extern const string* current_oname;
extern const meta_operation_info* current_mif;
extern const operation_info* current_inner_oif;
extern const operation_info* current_outer_oif;
extern size_t current_on; // Current operation number (1-based) in the
// meta-operation batch.
extern execution_mode current_mode;
// Total number of dependency relationships in the current action. Together
// with the target::dependents count it is incremented during the rule
// search & match phase and is decremented during execution with the
// expectation of it reaching 0. Used as a sanity check.
//
extern atomic_count dependency_count;
inline void
set_current_mif (const meta_operation_info& mif)
{
current_mname = &mif.name;
current_mif = &mif;
current_on = 0; // Reset.
}
inline void
set_current_oif (const operation_info& inner_oif,
const operation_info* outer_oif = nullptr)
{
current_oname = &(outer_oif == nullptr ? inner_oif : *outer_oif).name;
current_inner_oif = &inner_oif;
current_outer_oif = outer_oif;
current_on++;
current_mode = inner_oif.mode;
dependency_count.store (0, memory_order_relaxed); // Serial.
}
// Keep going flag.
//
// Note that setting it to false is not of much help unless we are running
// serially. In parallel we queue most of the things up before we see any
// failures.
//
extern bool keep_going;
// Reset the build state. In particular, this removes all the targets,
// scopes, and variables.
//
variable_overrides
reset (const strings& cmd_vars);
// Return the project name or empty string if unnamed.
//
inline const string&
project (const scope& root)
{
auto l (root[var_project]);
return l ? cast<string> (l) : empty_string;
}
// Return the src/out directory corresponding to the given out/src. The
// passed directory should be a sub-directory of out/src_root.
//
dir_path
src_out (const dir_path& out, const scope& root);
dir_path
src_out (const dir_path& out,
const dir_path& out_root, const dir_path& src_root);
dir_path
out_src (const dir_path& src, const scope& root);
dir_path
out_src (const dir_path& src,
const dir_path& out_root, const dir_path& src_root);
// Action phrases, e.g., "configure update exe{foo}", "updating exe{foo}",
// and "updating exe{foo} is configured". Use like this:
//
// info << "while " << diag_doing (a, t);
//
class target;
struct diag_phrase
{
const action& a;
const target& t;
void (*f) (ostream&, const action&, const target&);
};
inline ostream&
operator<< (ostream& os, const diag_phrase& p)
{
p.f (os, p.a, p.t);
return os;
}
void
diag_do (ostream&, const action&, const target&);
inline diag_phrase
diag_do (const action& a, const target& t)
{
return diag_phrase {a, t, &diag_do};
}
void
diag_doing (ostream&, const action&, const target&);
inline diag_phrase
diag_doing (const action& a, const target& t)
{
return diag_phrase {a, t, &diag_doing};
}
void
diag_did (ostream&, const action&, const target&);
inline diag_phrase
diag_did (const action& a, const target& t)
{
return diag_phrase {a, t, &diag_did};
}
void
diag_done (ostream&, const action&, const target&);
inline diag_phrase
diag_done (const action& a, const target& t)
{
return diag_phrase {a, t, &diag_done};
}
}
#include <build2/context.ixx>
#endif // BUILD2_CONTEXT_HXX
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